# Is the term ISO “totally fake”?



## Canon Rumors Guy (Feb 25, 2019)

> Tony Northrup has posted a video discussing the exposure term ISO and has deemed it “totally fake”. It’s an interesting take on the use of this legacy term in digital photography.
> *Tony summarizes:*
> 
> It’s just a post-processing instruction; generally, it doesn’t physically change anything about the picture taking process, unlike shutter speed and aperture.
> ...



Continue reading...


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## uri.raz (Feb 25, 2019)

Re #3 - the (sensor specific) signal to noise ratio limits how much the base ISO could be multiplied.


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## privatebydesign (Feb 25, 2019)

Oh dear we really are stretching on a Monday morning. I watched this video last week when it came out, and fstoppers come back video.

The truth is unless your sensor is iso invariant, which few are and no Canons are, then the iso setting is not irrelevant so the premise is immediately and obviously faulty.


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## Canon Rumors Guy (Feb 25, 2019)

privatebydesign said:


> Oh dear we really are stretching on a Monday morning. I watched this video last week when it came out, and fstoppers come back video.
> 
> The truth is unless your sensor is iso invariant, which few are and no Canons are, then the iso setting is not irrelevant so the premise is immediately and obviously faulty.



I liked the subject of the video, it's an interesting take. I'm more interested in the reactions I've read about it.


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## Pape (Feb 25, 2019)

i doubt my camera is better photoshop pictures than me.
tried make 5 stop underexposed 100 ISO pic as 1200 ISO pic . they were from different planet


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## RedPixels (Feb 25, 2019)

Even without iso invariant sensors, it is still valuable to know about it specifically for astrophotography. There comes a point where lower ISOs may introduce more noise with longer exposures on some sensors which is why you tend to see most shots at higher ISOs like 1600-3200.


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## crazyrunner33 (Feb 25, 2019)

At the end of the day, it's about understanding the tool you're using to maximize your results. 

Most Canon cameras are ISO invariant above 6400. You should always expose to the right until you hit that point. Once you hit your ISO invariance point, maximize as much light as you can for the situation (aperture, shutter, external light)while keeping the ISO at that invariant number(unless if there's different noise patterns at different numbers. Some cameras have minor differences at different ISO settings, even if they're ISO invariant). 

Some Sony sensors used in Nikon and Sony have two different levels of ISO invariance. One below 640 ISO and one above. ISO and ETTR still matters to a certain extent.


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## crazyrunner33 (Feb 25, 2019)

RedPixels said:


> Even without iso invariant sensors, it is still valuable to know about it specifically for astrophotography. There comes a point where lower ISOs may introduce more noise with longer exposures on some sensors which is why you tend to see most shots at higher ISOs like 1600-3200.



It's also worth pointing out that an ISO invariant sensor doesn't automatically mean it's better than one that depends on ISO. The Canon 6D is a great example for astrophotography, it still hangs in with today's crops of cameras in certain scenarios.


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## LDS (Feb 25, 2019)

Canon Rumors Guy said:


> Low ISO could be eliminated by simply using image averaging



I'm not sure it would yield the same "graphical" results of a long exposure. Anyway, that's just a single use case for low ISO.


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## crazyrunner33 (Feb 25, 2019)

LDS said:


> I'm not sure it would yield the same "graphical" results of a long exposure. Anyway, that's just a single use case for low ISO.



That suggestion works similar to Google's Night Sight, which is extremely impressive. Like you said, it's still a tool that has limitations and isn't a one stop solution. I'm also wondering if the wording is meant to say high ISO could be eliminated instead of low ISO. The Night Site I'm using normally shoots at base ISO 50.

Edit:
It appears that Google's Night Site is probably a modification and early adaption of Sony Semiconductor's tools they're offering with some of their newer sensors. It says right in the marketing material that it's using a few frames at 60 fps. The shutter at the most would then be 1/60th. 

https://www.sony-semicon.co.jp/products_en/IS/cmos/index.html


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## Kit. (Feb 25, 2019)

Is there really a standard for "ISO" values for a digital sensor?

I remember that the ISO standard about the negatives specified a particular optical density of the film that shall be achieved during exposure (and then standard processing). Which actually led to the situation where low-contrast film was being slightly underexposed at their standard ISO.

So, ISO, in a sense, was already "fake" in the film era.


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## LDS (Feb 25, 2019)

crazyrunner33 said:


> 'm also wondering if the wording is meant to say high ISO could be eliminated instead of low ISO



IMHO it's on both sides - low ISO + ND filter to extend the exposure, or high ISO for low-light capture. As image averaging started IIRC in astrophotography, it's probably more common to think about the latter than the former - where you may want smooth water/clouds and "remove" moving elements - it could work, albeit I'm not sure if they would be enough alike.

What makes me dubious is you would be "prisoner" of algorithms upon which one may have little control - and if artifacts appear, it may be difficult to get rid of them. How a long exposure/ND filter work is much more deterministic. Sure, if you perform the averaging/merging yourself you may have far more control, but it's also a bigger effort, and would increase the storage needs.


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## sanj (Feb 25, 2019)

I need to relearn basics of photography.


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## PavelR (Feb 25, 2019)

Kit. said:


> Is there really a standard for "ISO" values for a digital sensor?
> 
> I remember that the ISO standard about the negatives specified a particular optical density of the film that shall be achieved during exposure (and then standard processing). Which actually led to the situation where low-contrast film was being slightly underexposed at their standard ISO.
> 
> So, ISO, in a sense, was already "fake" in the film era.


Yes, there is: ISO (organization) standard 12232:2006 and 2019


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## SkynetTX (Feb 25, 2019)

1., As anyone else sometimes Tony is wrong. The term ISO speed is used as a definition for the sensitivity of the sensor (film) therefore it can not be fake,
2., The higher the ISO (and the smaller the sensor) the more the noise therefore it DOES effect your photos,
3., ISO also effects shutter speed that also effects your pictures since at shoter shutter speeds you have to worry less about blurry pictures.
4., ISO speed is part of the exposure triangle – see above – so regardless the value it will affect your picture.


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## AlanF (Feb 25, 2019)

crazyrunner33 said:


> At the end of the day, it's about understanding the tool you're using to maximize your results.
> 
> Most Canon cameras are ISO invariant above 6400. You should always expose to the right until you hit that point. Once you hit your ISO invariance point, maximize as much light as you can for the situation (aperture, shutter, external light)while keeping the ISO at that invariant number(unless if there's different noise patterns at different numbers. Some cameras have minor differences at different ISO settings, even if they're ISO invariant).
> 
> Some Sony sensors used in Nikon and Sony have two different levels of ISO invariance. One below 640 ISO and one above. ISO and ETTR still matters to a certain extent.



Most Canon sensors are isoinvariant above iso640, not 6400. Maybe you made a typo.


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## Mt Spokane Photography (Feb 25, 2019)

ISO test procedures were developed by committees from Camera manufacturers and are complex and even allowed to vary by camera design, type of metering, etc. The last update was in 2006. If and when it no longer works, it will be updated again as it has been many many times.

Right now, a exposure at ISO100, f/8, 1/125 sec still produces a good exposure. If you boost or reduce the exposure, it will be incorrect. You may be able to correct that error by digital manipulation of the image file, but the ISO value to get a correct exposure in camera still works.

The issue is how to rate the ISO of a digital sensor when it contains lots of noise processing circuitry that distorts the conventional rating method of looking at the output of the sensor. 

So, ISO still works, but, as in film, changes that reduce inherent noise allow you to boost the apparent ISO, it was done in film by longer processing times, it can be done in digital by changing exposures and digitally manipulating the resulting files, and eventually, a new rating will come out.


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## Mt Spokane Photography (Feb 25, 2019)

Kit. said:


> Is there really a standard for "ISO" values for a digital sensor?
> 
> I remember that the ISO standard about the negatives specified a particular optical density of the film that shall be achieved during exposure (and then standard processing). Which actually led to the situation where low-contrast film was being slightly underexposed at their standard ISO.
> 
> So, ISO, in a sense, was already "fake" in the film era.



Yes, and film was also marketed with higher ISO ratings, but was the same exact film but with longer processing times. A similar bunch of comments were made.


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## AlanF (Feb 25, 2019)

privatebydesign said:


> Oh dear we really are stretching on a Monday morning. I watched this video last week when it came out, and fstoppers come back video.
> 
> The truth is unless your sensor is iso invariant, which few are and no Canons are, then the iso setting is not irrelevant so the premise is immediately and obviously faulty.



The better Canon sensors are isoinvariant above about iso160-200, which covers much of their range: see
http://www.photonstophotos.net/Char... X Mark II,Canon EOS 5D Mark IV,Canon EOS 80D

for 5DIV (=EOS R), 80D, 1dXII


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## rjbray01 (Feb 25, 2019)

I thought it was yet another totally excellent video by Tony Northrup. When I started photography in earnest about three years ago I watched tons of Tony's videos and found them both informative and inspiring.

Personally I feel I owe him a lot.

I think he is a great communicator and pitches things at just the right level - at least for me - I'm currently doing an honours degree in maths and physics and rarely feel that Tony is being patronising or completely dumbed down ... but equally he is pitching for a wide audience and definitely not for camera technicians.

Like all good teachers he has to "pitch" the level of what he is teaching, and inevitably that involves making some simplifications - which are essentially inaccuracies.

Keep up the good work Tony !


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## tmroper (Feb 25, 2019)

On #2, film was (and still is) the same way. "Box speed" is only a rough suggestion, and each photographer must do their own tests, and calibrate things accordingly. So your light meter only "works as you expect" after you've determined what those expectations are. Also, not all light meters are the same, so you have to check that, too. Oh, and if you print in the darkroom, different batches of paper will be a little different, so you can't just use the same time and aperture from one to make identical prints later (that's what my darkroom instructor/guru says anyway--I'm not at that level yet). So yeah, life's not as simple as the marketing people claim. But you should know that already.


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## Kit. (Feb 25, 2019)

PavelR said:


> Yes, there is: ISO (organization) standard 12232:2006 and 2019


So, basically (for shooting in RAW): "It's when you have a half stop extra to overexpose a 100% diffuse white object without highlight clipping".


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## knight427 (Feb 25, 2019)

I found the following link to be the most informative guide to understanding ISO as gain, with one layer drilling down into the details to be aware of the difference between upstream and downstream read noise (at least as it related to astrophotogrpahy use cases). 

http://dslr-astrophotography.com/iso-dslr-astrophotography/

But Tony's video is far more entertaining with high conflict generation potential, and therefore will reach far more people.


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## magarity (Feb 25, 2019)

Horseless carriages don't have horses pulling them but the engine power is described as 'horsepower'. So why not 'ISO' for 'sensitivity'? Is the problem that it isn't standardized?


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## AlanF (Feb 25, 2019)

Just came across this by jrista, who used to make great contributions here (https://photo.stackexchange.com/questions/25917/why-is-sensor-sensitivity-called-iso)
"Just a note. When it comes to digital sensor "sensitivity", the term sensitivity in that context is actually a bit of a misnomer. A digital sensor is a fixed, linear, analog device. It always has the same _real_ sensitivity. When you adjust the ISO setting to a higher level, all that really does is reduce the maximum saturation point. The sensor does not detect more light...it detects the same, so its still just as "sensitive". Its just that instead of pure white occurring at say 40,000 electrons in a pixel (ISO 100), it occurrs at 20,000 electrons (ISO 200), or 10,000 electrons (ISO 400), etc " jrista


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## peterzuehlke (Feb 25, 2019)

RedPixels said:


> Even without iso invariant sensors, it is still valuable to know about it specifically for astrophotography. There comes a point where lower ISOs may introduce more noise with longer exposures on some sensors which is why you tend to see most shots at higher ISOs like 1600-3200.


For performance photography too. When you are at the bleeding edge of exposure and are trying to make decisions between f stop, shutter speed and noise, ISO helps in that judgement. I often end up shooting at f/1.4 to f/2.8 when I would like to be at f/4 for DOF but I would also like to be above 1/125s because of subject movement but don't want to go too high ISO because of noise (I am usually at 6400 or higher)


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## gwooding (Feb 25, 2019)

AlanF said:


> The better Canon sensors are isoinvariant above about iso160-200, which covers much of their range: see
> http://www.photonstophotos.net/Charts/PDR.htm#Canon EOS 1D X Mark II,Canon EOS 5D Mark IV,Canon EOS 80D
> 
> for 5DIV (=EOS R), 80D, 1dXII
> View attachment 183314


I do not believe that it is very easy to determine a sensors ISO-in-variance by looking at the sensors dynamic range.

The same site however does provide charts for what I believe to be an indication of ISO-in-variance. They call it "Photographic Dynamic Range Shadow Improvement versus ISO".

http://www.photonstophotos.net/Gene...ographic_Dynamic_Range_Shadow_Improvement.htm

If I understand correctly, what this chart shows is how much extra shadow detail is gained by increasing the ISO instead of raising an underexposed image in post. In other words whether it is worth using higher ISO's instead of just underexposing and raising in post.
http://www.photonstophotos.net/Charts/PDR_Shadow.htm#Canon EOS 1D X Mark II,Canon EOS 6D Mark II,Nikon D850,Pentax K-1



From this chart we can see that basically the closest of the 4 cameras to ISO-in-variance is the Pentax K-1 which only sees about a 0.2EV improvement increasing the ISO over base,

The Nikon D850 is ISO-in-variant above 500, with 500 yielding about a 1EV improvement.

The 1DX MK2 however only appears to see a no significant improvement once we get to about ISO 3200 (1.7 EV improvement). I suppose you could argue that the 0.3EV improvement from 800 to 3200 isn't much.

With the 6D MK2 you can clearly see that using higher ISO's are very beneficial (interestingly you can also easily see where the analogue gain is used and where the digital gain is used).

I also believe the preceding chart illustrates that the only camera of the ones I picked only the Pentax conforms to Tony Northrup's ideas (I must confess I didn't watch the video I just read the summary provided). Clearly if we look at something like the 6D2 the ISO setting (at least the full stops) has a big difference and works as you would expect although increasing ISO by one stop only gives you about 0.8EV extra sensitivity.

The quote by Jrista provided by AlanF is 100% correct. I just thought I could expand a bit on what increasing the ISO in camera actually does. As mentioned the signal coming off the sensor is an analogue signal so it needs to be read by an analogue to digital converter (ADC) which quantizes the signal (converts an analogue voltage into a digital number between 0 and 2^14 for a 14-bit ADC). This process introduces noise. If we then amplify the signal after this (raise in post or digital ISO) we also increase the magnitude of the noise thus we don't get as much improvement as we expected. One way around this is to amplify the signal before the ADC reads it, this reduces the headroom but normally improves the signal to noise ratio so as long as you are not clipping highlights it should be an improvement.

If the noise introduced by the ADC is negligible and the ADC has sufficient bit depth we can theoretically do all amplification digitally without any adverse effects, this would be a perfect ISO-in-variant sensor. The introduction of the low noise on sensor ADC's has definitely reduced the need for pre-amplification or perhaps eliminated it completely with certain cameras. I suspect the Pentax K-1 either has such good ADC's that it doesn't benefit from them or it doesn't actually have them (I think the latter is more likely since that would explain why the 1DX MK2 has better dynamic range at ISO's over 800).
http://www.photonstophotos.net/Charts/PDR.htm#Canon EOS 1D X Mark II,Pentax K-1


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## AlanF (Feb 25, 2019)

gwooding said:


> I do not believe that it is very easy to determine a sensors ISO-in-variance by looking at the sensors dynamic range.
> 
> The same site however does provide charts for what I believe to be an indication of ISO-in-variance. They call it "Photographic Dynamic Range Shadow Improvement versus ISO".
> 
> ...



Very good points, which fit in with nice discussions such as this: https://photographylife.com/iso-invariance-explained

However, a simple way of looking for isoinvariance is to look at DR vs iso charts and homing in on the regions where DR decreases linearly with iso- see:
http://www.dslrbodies.com/cameras/camera-blogs/the-d5d500-blog/iso-variance.html

"Simplest explanation: An ISO invariant sensor is going to have a dynamic range chart that has a constant slope downwards as you increase ISO values. An ISO variant camera is going to have ups and downs, sometimes only a couple of clear jumps at particular ISO values where the digital gain is changed, sometimes changes at all values, as with the D5 low ISO values." Thom Hogan

But, I would add a further mathematical criterion about the slope of the plot:
Isoinvariance is characterised by a linear plot of DR vs ln(2)iso of slope 1, (where ln(2)iso = ln to base 2 of the iso)

This criterion is obeyed by the 5DIV, 80D, 1DXII in the linear regions pretty well. The Pentax K-1 fits it close to perfect.


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## RGF (Feb 25, 2019)

Difference between 2 cameras and LENS. Could the difference be the T factor on the lens. a full stop is a lot but 1/3 to 2/3 is possible!


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## Michael Clark (Feb 25, 2019)

Tony Northrup is the YouTube version of Ken Rockwell. He says just enough that is actually correct to make the rest of what he says dangerous.

He's in it for the clicks (money), and he'll say whatever he thinks will get the most clicks. Everyone in any kind of media today (and these days, YouTube is about as financially viable for many folks as what we call the "traditional media") follows the model of Howard Stern: It doesn't matter if they like or hate the way you are constantly stirring the pot, as long as they are talking about you and listening/watching you.


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## Graphic.Artifacts (Feb 25, 2019)

I'm no expert, but I'd be very surprised if Canon wasn't using some sort of analog gain prior to the A/D circuits at higher ISO's. I like Tony Northrup and most of what he say's I'd agree with regarding ISO. However, if analog signal amplification is being used by Canon at higher ISO's, those images will have different properties than those that are "under-exposed" and lifted in post. That being said, within my normal range for handheld shooting, I rarely worry about ISO and typically shoot M/auto ISO and sort exposure out in post. I'd certainly like to see complete ISO invariance but I think Canon has a way to go on that.


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## AlanF (Feb 25, 2019)

JS5 said:


> Yet another reason how and why digital photography ruined the business... ( except for them )
> A baboon can shoot now ! And why shoot it in one frame ? Let's fix it in post ! LMAO !
> I miss the days when photographers actually knew their trade...
> I wish digital photography would die and go away already.



It's now Planet of the Baboons, and I am happy to be one of them. And you know what, I know the tools of the digital trade, and a lifetime ago a I developed and enlarged my own negs.


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## neuroanatomist (Feb 25, 2019)

privatebydesign said:


> ...the premise is immediately and obviously faulty.


On one hand, this statement is very appropriate for pretty much any ‘technical’ video from Northrup. 

On the other hand, from his perspective I suspect the real premise for all his videos is simply to generate clicks and thus income, and thus any misinformed piece of clickbait can be a success in those terms.


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## dtaylor (Feb 25, 2019)

I like the videos that the Northrup's put out, but Tony does get caught up in memes at times. And ISO invariance is a meme.

1 - Even ISO invariant sensors are not ISO invariant because they typically have at least two analog gain stages. That's why fstoppers saw a difference testing arguably the highest DR / most ISO invariant sensor made. Older sensors had more stages and complicating factors (read noise). Future sensors might also have more stages and complicating factors. Incorporating the belief that you can ignore ISO will lead to mistakes.

2 - Outside of astrophotography knowing the ranges of invariance for a sensor doesn't help you at all. If you're in an AE mode are you going to constantly fight your meter with your EC dial because your sensor is ISO invariant? If you're in full manual are you going to constantly recalculate your meter readings? On mirrorless are you going to give up exposure preview? And...what happens to your back-of-camera shot review when you underexpose by 5 stops?

Saying it doesn't matter if you shoot at X and push to Y in post is the same thing as saying it doesn't matter if you go ahead and shoot at Y so that your meter, AE, EVF preview, and shot review are all in sync and working as designed. Which is what everyone does any way.

3 - ISO invariance is terribly confusing to new photographers and will lead to mistakes even if they are operating within an invariant range.

I don't know why this meme is pushed. DPReview dedicates an entire page of each review to this meme, and I swear it's just so that they can bring up the DR topic again. Now the Northrup video. _I can just set my camera to ISO 640 and push to ISO 25,600 in post._ Or...*or*...you could just set the camera to ISO 25,600 and not complicate meter readings, previews, exposure settings, and post shot reviews.

Side note: ETTR did not become a technique due to DR or ISO invariance in early sensors. It became a technique to maximize shadow tonality. Due to the nature of how pixels and ADCs work higher zones (say, zone 8) have finer tonality than lower zones (zone 2). If you shift your exposure to the right on the histogram then adjust it back down in post your shadows will have finder gradations. _This remains true today even on so-called ISO invariant sensors._

I just recently watched a video by a professional architecture photographer who uses a 100mp Phase One. He brought up the Phase One's DR but mentioned he never pushes shadows any way because he blends two exposures in those situations. Why? For better tonality. I had to laugh when he said it because it seems the photographic community has forgotten this in the rush to see who can underexpose their cat by the greatest amount and still get a usable print.


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## photo212 (Feb 25, 2019)

Dynamic range, color range/spectrum. Gee, ISO setting is something that might actually matter.

The upper ISO setting does matter. The manufacturer decides what is the useful ISO upper limit. Sure, they could allow you to go well beyond that number, but then people would post images of this thousands of dollars of camera that look quite crappy. If the upper limit did not matter, try comparing ISO 1600 a Canon 10D versus a 80D (or whatever more modern sensor).

https://www.mattgranger.com/tutorials/item/238-the-real-downsides-to-high-iso


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## dtaylor (Feb 25, 2019)

Graphic.Artifacts said:


> I'm no expert, but I'd be very surprised if Canon wasn't using some sort of analog gain prior to the A/D circuits at higher ISO's. I like Tony Northrup and most of what he say's I'd agree with regarding ISO. However, if analog signal amplification is being used by Canon at higher ISO's, those images will have different properties than those that are "under-exposed" and lifted in post. That being said, within my normal range for handheld shooting, I rarely worry about ISO and typically shoot M/auto ISO and sort exposure out in post. I'd certainly like to see complete ISO invariance but I think Canon has a way to go on that.



*Sony* sensors have two gain stages.


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## Quarkcharmed (Feb 25, 2019)

The Tony's statements are oversimplified to the point where the whole video becomes just a lie. In general he's giving a lot of misleading information when it comes to the technical details, I don't think he's a good source. His channel is well presented and has many subscribers but often broadcasts technically inaccurate and misleading information.

The signal from the sensor first gets amplified in *analog* amplifier before it gets through the ADC. Then it becomes a digital signal and can also be amplified digitally. Analog amplification also amplifies the noise but it's more accurate than digital. So setting ISO 800 in camera is *not* the same as adding +3ev to an ISO 100 image in Lightroom.

For Canon, as far as I remember, analog amplification goes for ISO 200, 400, 800, and interim values are obtained through analog amplification + digital up/down scaling. Say ISO 320 is analog amplification to ISO 400 then digital downscaling. (The numbers above are just examples as I'm too lazy to search for more accurate figures).
Base ISO 100 is called 'base' because it doesn't get amplified, just converted to digital, thus it's the ISO with the most accurate data possible.


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## Quarkcharmed (Feb 25, 2019)

knight427 said:


> I found the following link to be the most informative guide to understanding ISO as gain, with one layer drilling down into the details to be aware of the difference between upstream and downstream read noise (at least as it related to astrophotogrpahy use cases).
> 
> http://dslr-astrophotography.com/iso-dslr-astrophotography/
> 
> But Tony's video is far more entertaining with high conflict generation potential, and therefore will reach far more people.



Good one, I didn't see your post before writing my comment above. Only that 'reaching more people' and 'providing accurate information' are totally different goals and I don't think Tony pursues the latter one.


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## hamoser (Feb 25, 2019)

sanj said:


> I need to relearn basics of photography.


Maybe you do. Just don't try to learn them from Tony.


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## rjbray01 (Feb 25, 2019)

JS5 said:


> Yet another reason how and why digital photography ruined the business... ( except for them )
> A baboon can shoot now ! And why shoot it in one frame ? Let's fix it in post ! LMAO !
> I miss the days when photographers actually knew their trade...
> I wish digital photography would die and go away already.


Yeah just like the days of professional typists which were completely ruined by digital word processing ...


JS5 said:


> Yet another reason how and why digital photography ruined the business... ( except for them )
> A baboon can shoot now ! And why shoot it in one frame ? Let's fix it in post ! LMAO !
> I miss the days when photographers actually knew their trade...
> I wish digital photography would die and go away already.


You ain't seen nothing yet ... Only a matter of time until lightroom is built into the camera and will automatically crop, post process and even rate your pictures completely automatically ...


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## Quarkcharmed (Feb 26, 2019)

rjbray01 said:


> Yeah just like the days of professional typists which were completely ruined by digital word processing ...
> 
> You ain't seen nothing yet ... Only a matter of time until lightroom is built into the camera and will automatically crop, post process and even rate your pictures completely automatically ...


Postprocess, rate, upload to social networks, view them, enjoy, like and then delete - all completely automatically, you won't even need to see the images.


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## bhf3737 (Feb 26, 2019)

Misleading information. The meaning of sensitivity, gain, iso-invariant, etc., are simply wrong in his presentation. 
And interpretation of F-stop (should be T-stop) is also incorrect.
There was a time that scientists wrote about science and politicians talked politics. 
Nowadays every clown with a front facing camera can do both!!


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## Ozarker (Feb 26, 2019)

JS5 said:


> Yet another reason how and why digital photography ruined the business... ( except for them )
> A baboon can shoot now ! And why shoot it in one frame ? Let's fix it in post ! LMAO !
> I miss the days when photographers actually knew their trade...
> I wish digital photography would die and go away already.


Get off my lawn!


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## unfocused (Feb 26, 2019)

JS5 said:


> Yet another reason how and why digital photography ruined the business... ( except for them )
> A baboon can shoot now ! And why shoot it in one frame ? Let's fix it in post ! LMAO !
> I miss the days when photographers actually knew their trade...
> I wish digital photography would die and go away already.



I miss the days when photographers actually knew their trade. Back in the good old days when we took the darkroom with us, brushed our plates with emulsion and then went back in the van and developed the plate before the emulsion dried.


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## knight427 (Feb 26, 2019)

unfocused said:


> I miss the days when photographers actually knew their trade. Back in the good old days when we took the darkroom with us, brushed our plates with emulsion and then went back in the van and developed the plate before the emulsion dried.



Ugg ug ug, uug ug uug ugh! Ug ugugug.


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## 3kramd5 (Feb 26, 2019)

dtaylor said:


> *Sony* sensors have two gain stages.


Not exactly. All sensors have analog conversion gain and at least almost all sensors have digital gain; Sony is no different from anyone else there.

For many years Sony has licensed a schema from Aptina to change that conversion gain. It’s not a unique “stage”. It’s really just a change in the capacitance of the circuit which increases the gain passively.


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## RGF (Feb 26, 2019)

Try the following experiment - shoot a raw image at ISO 2000-6400, under exposed by 3-5 stops. Then in LR, increase the exposure by the 3-5 stops you underexposed the image.

Repeat this time ISO 3-5 stops higher, properly exposed. Of course shot in manual mode. 

Compare the images

My experience and testing tells the higher ISO in the camera gives a better exposure than lower camera ISO and adding exposure in LR.


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## Pape (Feb 26, 2019)

Well now i understand why super teles still are 5,6F even isos lot higher .
Iso performance havent truelly improved from film days.


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## privatebydesign (Feb 26, 2019)

Pape said:


> Iso performance havent truelly improved from film days.



Clearly you never shot film! Improvements in ISO performance are the single biggest leap in IQ for decades. AF is nice, IS can be a real boon, but the improvements in ISO even low down are good, at higher figures they are nothing short of spectacular.

I can print from 400 ISO digital files to a higher standard than I ever could with same size 50 ISO slide film. I can easily deliver images at 10,000 ISO from my current digital camera yet film was rarely above 800 ISO, with a resigned acceptance of limitations and poor IQ even at small reproduction sizes at 1,600 ISO.


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## Pape (Feb 26, 2019)

maybe things we can do with photoshop are improved from film days,noise reduction tricks
Difficult compare ,i just watched my slides on wall paper ,didnt got computer then  never printed anything
i still got 300d camera ,not really good to compare new ones . Ill hope ill get rp soon.
I wonder if resulotion of pictures is actually growed more than Iso performation ,so actually more difficult take unshaken hand hold picture with 5,6F super tele than it was on film days?


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## Kit. (Feb 26, 2019)

Pape said:


> maybe things we can do with photoshop are improved from film days,noise reduction tricks


Actually, silver halide film is a really crappy sensor for light measurement. You need exactly 3 photons per grain to turn the grain black. 2 photons are ignored, all the photons absorbed by the grain after the first 3 are ignored as well.


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## #verweyen (Feb 26, 2019)

Hi,

i have take some shots with my Canon EOS R and 6D Mark II and can´t push a under exposed pictures like Tony shows in his video.
I think, canon sensors work different.

Here the raw´s

https://www.dropbox.com/sh/v16mee3nnqw7b7x/AAD2ZHMqdCSgIp6AgYutyTFUa?dl=0

Greetings, Dirk


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## Del Paso (Feb 26, 2019)

rjbray01 said:


> Yeah just like the days of professional typists which were completely ruined by digital word processing ...
> 
> You ain't seen nothing yet ... Only a matter of time until lightroom is built into the camera and will automatically crop, post process and even rate your pictures completely automatically ...


Time is already here!
Zeiss has just launched a small FF camera with built-in Lightroom!


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## GMCPhotographics (Feb 26, 2019)

privatebydesign said:


> Clearly you never shot film! Improvements in ISO performance are the single biggest leap in IQ for decades. AF is nice, IS can be a real boon, but the improvements in ISO even low down are good, at higher figures they are nothing short of spectacular.
> 
> I can print from 400 ISO digital files to a higher standard than I ever could with same size 50 ISO slide film. I can easily deliver images at 10,000 ISO from my current digital camera yet film was rarely above 800 ISO, with a resigned acceptance of limitations and poor IQ even at small reproduction sizes at 1,600 ISO.


I found in the film days that the native noise in the drum / film / slide scanner has a lot to do with the images final noise. Noise interference patterns occur between the film grain particle size and the CCD pattern noise in the scanner. Iso 200 Fuji Chrome had more noise than 800 iso print scans on my 2700 dpi scanner (approx 11.9 mp equivalent). Iso 50 and 100 looked way better...as did 400 iso. Certain brands of film at certain iso's seems to create mega noise due to the interference patterns. A friend of mine used a slightly higher resolution 4000dpi scanner only to find his beloved Velvia 50 scans were riddled with high iso noise and were unusable. Were as scans from my machine were far smoother at the lower native dpi. So yes...iso noise is a thing. Sensor noise / pipeline noise...it's all physical real world issues. 
I used to wonder if anyone would develop film profiles (like the digital modelling in guitar effects). But the reality is that most modern sensors far far exceed the dynamic range, contrast range and noise levels available on slide medium.


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## Bahrd (Feb 26, 2019)

Kit. said:


> Actually, silver halide film is a really crappy sensor for light measurement. You need exactly 3 photons per grain to turn the grain black. 2 photons are ignored, all the photons absorbed by the grain after the first 3 are ignored as well.



Wow! Now I know what was Dr. Fossum's Quanta Image Sensor inspired by!


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## bbb34 (Feb 26, 2019)

"fake" is something that is not real, but made to appear real.

"ISO" is a legacy term for the combination of sensitivity and gain. Sensitivity and gain are both, very real and very important for photography. There is nothing fake about it. Sensitivity includes quantum efficiency and fill factor. Gain is about the analogue amplification of the signal between sensor and analog-to-digital converter.

I wish camera manufacturers would call sensitivity and gain by their names, and use proper units. And use a logarithmic scale instead of ridiculous large numbers.


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## crazyrunner33 (Feb 26, 2019)

AlanF said:


> Most Canon sensors are isoinvariant above iso640, not 6400. Maybe you made a typo.



It depends on the camera, 5D Mark IV and 80D are decent, I didn't realize how clean they were. But the 7D Mark II, 6D Mark II, 5DS R are not ISO invariant until at least after 3200. The 6400 number is the one that pops into my head when playing a lot with dual ISO on Magic Lantern, 6400 ISO definitely applies for the 6D and 5D Mark III. This is based on my observations of the noise that appears when bumping the exposures.


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## Hector1970 (Feb 26, 2019)

I don't mind Tony Northrup in general. I think he is honest enough in his opinions.
He also has to get page views and things like this pull people in to argue.
Me - I'm quite happy with ISO and how its set up currently in photography.
While it may be a little artificial it is in reality a third point to the exposure triangle from the recorded image perspective.
The article and the comments here brought a few things to my mind which I'd appreciate feedback.

In theory should it be possible to use high ISO to capture the image but say the raw file contain the information from a lower ISO level if ISO is invariant. It would mean if you overdid the ISO you could recover to a more appropriate (less noisy) level?

The second is in the future instead of using physical filters like neutral denstity and graduated neutral densities will the camera be able to desensitize the sensor. ie: Allow for 30 s exposure by say not continuously capturing the light or having the top half less sensitive than the bottom half?
Would this ever be better than a physical filter?
I think Olympus has some sort of electronic neutral density filter in that new big camera they've made


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## Tom W (Feb 26, 2019)

Canon Rumors Guy said:


> Continue reading...



Personally, I'd like to see them get back to the standard. The "sunny 16 rule" should work the same on all devices. 
I don't like the idea of eliminating it because ISO (or digital/analog gain) IS part of the equation that determines exposure level, or how much brightness is recorded.


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## knight427 (Feb 26, 2019)

Hector1970 said:


> I don't mind Tony Northrup in general. I think he is honest enough in his opinions.
> He also has to get page views and things like this pull people in to argue.
> Me - I'm quite happy with ISO and how its set up currently in photography.
> While it may be a little artificial it is in reality a third point to the exposure triangle from the recorded image perspective.
> ...



Armature disclaimer (you get what you pay for):

1- ISO in-variance still hits the wall of clipping. One you've filled your light bucket, there is no way to recover that information.

2- I bet there are lots of problems I don't even know about with the eND filters, but one I can think of relates to sampling errors of motion. If you are turning the senor off and on to simulate an ND filter, the rate at which you do this is going to effect the smoothness of motion. Maybe you can sample fast enough so it doesn't matter, but even in that case you'll end up with "digital purists" who won't want their 1s and 0s sampled at any frequency (cue the debate of 44kHz sampling in audio).


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## dtaylor (Feb 26, 2019)

GMCPhotographics said:


> I found in the film days that the native noise in the drum / film / slide scanner has a lot to do with the images final noise. Noise interference patterns occur between the film grain particle size and the CCD pattern noise in the scanner. Iso 200 Fuji Chrome had more noise than 800 iso print scans on my 2700 dpi scanner (approx 11.9 mp equivalent). Iso 50 and 100 looked way better...as did 400 iso. Certain brands of film at certain iso's seems to create mega noise due to the interference patterns. A friend of mine used a slightly higher resolution 4000dpi scanner only to find his beloved Velvia 50 scans were riddled with high iso noise and were unusable. Were as scans from my machine were far smoother at the lower native dpi. So yes...iso noise is a thing.



This used to be referred to as grain aliasing. (http://www.photoscientia.co.uk/Grain.htm) It was less about CCD noise and more about grain size versus scan resolution. But, yeah, certain films on certain scanners would have terrible grain. I'm surprised to hear about Velvia 50 because that always seemed to scan well for me at 2700 dpi or 4000 dpi.

That said, even compared to darkroom prints digital has a huge ISO advantage. ISO 3,200 shots from current APS-C sensors have a noise pattern comparable to tight grained ISO 400 print film. FF is comparable at ISO 12,800. I remember not wanting to shoot film higher than ISO 400 in 35mm format, but I have no reservation about pushing to 12,800 with digital FF.



> I used to wonder if anyone would develop film profiles (like the digital modelling in guitar effects). But the reality is that most modern sensors far far exceed the dynamic range, contrast range and noise levels available on slide medium.



Yep. I do miss the color rendering of certain films, and the pre-canned film plugins never seem to get them quite right. But the flexibility I have in ACR/PS/LR to produce the colors and look I want far exceeds anything I ever had with film.


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## BeenThere (Feb 26, 2019)

Mt Spokane Photography said:


> Yes, and film was also marketed with higher ISO ratings, but was the same exact film but with longer processing times. A similar bunch of comments were made.


Not really. Larger silver Halide grains were used for faster film. This made each grain more sensitive to light and also gave the film a more grainy appearance. The user could boost a low iso film to an apparently higher value by boosting development time, but this would also change the film gamma.


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## AlanF (Feb 26, 2019)

crazyrunner33 said:


> It depends on the camera, 5D Mark IV and 80D are decent, I didn't realize how clean they were. But the 7D Mark II, 6D Mark II, 5DS R are not ISO invariant until at least after 3200. The 6400 number is the one that pops into my head when playing a lot with dual ISO on Magic Lantern, 6400 ISO definitely applies for the 6D and 5D Mark III. This is based on my observations of the noise that appears when bumping the exposures.



I routinely used iso640 on my 7DII and now iso640 on my 5DSR as it is within the isoinvariant region and gives me a fast enough shutter speed for much of my work. I have replotted the data from photonstophotos and you can see that iso640 is in the linear region (from about iso500 for the 5DSR and lower from the 7DII.


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## LSXPhotog (Feb 26, 2019)

Michael Clark said:


> Tony Northrup is the YouTube version of Ken Rockwell. He says just enough that is actually correct to make the rest of what he says dangerous.
> 
> He's in it for the clicks (money), and he'll say whatever he thinks will get the most clicks. Everyone in any kind of media today (and these days, YouTube is about as financially viable for many folks as what we call the "traditional media") follows the model of Howard Stern: It doesn't matter if they like or hate the way you are constantly stirring the pot, as long as they are talking about you and listening/watching you.



Thank you for speaking my mind. When I was first getting started in the publishing industry I knew a staff photographer just like him. That guy knew -or felt he knew- a lot about photography and would talk your ear off about it. We actually had a handful of good conversations about it over the years. However, he ultimately lost his job to me because he couldn't actually take photos with a camera. He just knew the technical aspects of it but editors would constantly complain about the images he delivered to them. (He had several...MANY reshoots over his tenure there.)

Focusing too much on the technical side of photography can't be fun. I have seen plenty of photos the Northrups share on their channel to know that they are _THAT_ guy I worked with. They know a lot about the technical side of photography - enough to be dangerous - but they may lack the creativity and ability to be successful photographers beyond the stock photography business they had.


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## magarity (Feb 26, 2019)

AlanF said:


> Just came across this by jrista, who used to make great contributions here (https://photo.stackexchange.com/questions/25917/why-is-sensor-sensitivity-called-iso)
> "Just a note. When it comes to digital sensor "sensitivity", the term sensitivity in that context is actually a bit of a misnomer. A digital sensor is a fixed, linear, analog device. It always has the same _real_ sensitivity. When you adjust the ISO setting to a higher level, all that really does is reduce the maximum saturation point. The sensor does not detect more light...it detects the same, so its still just as "sensitive". Its just that instead of pure white occurring at say 40,000 electrons in a pixel (ISO 100), it occurrs at 20,000 electrons (ISO 200), or 10,000 electrons (ISO 400), etc " jrista



A CCD image sensor is an analog device (original 1D, and the old Kodak Canons) and have analog to digital converters. A CMOS image sensor is a digital device (any Canon since the 1D). Amusingly enough CMOS digital goes through a digital to analog conversion and then converted back to digital again later, but they're not analog devices themselves.


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## Jack Douglas (Feb 26, 2019)

Hmm, I thought light was an analog quantity. 

Jack


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## Kit. (Feb 26, 2019)

magarity said:


> A CCD image sensor is an analog device...
> A CMOS image sensor is a digital device...


What do you mean by that?


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## 3kramd5 (Feb 26, 2019)

Kit. said:


> What do you mean by that?


I wondered the same.


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## BeenThere (Feb 26, 2019)

Jack Douglas said:


> Hmm, I thought light was an analog quantity.
> 
> Jack


Count the digital photons.


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## knight427 (Feb 26, 2019)

BeenThere said:


> Count the digital photons.



Only after the wavelengths have been sorted through the filter array.



Kit. said:


> What do you mean by that?



I don't get what magarity is saying either. I believe an imagining sensor is simply an array of transducers, transforming light waves into proportional electronic waves (much like a microphone transduces pressure waves into electronic waves). I dunno, maybe the audio analogy doesn’t hold up.


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## magarity (Feb 26, 2019)

Kit. said:


> What do you mean by that?


Because a CMOS device converts each pixel's output to digital immediately whereas a CCD keeps the pixels' signals analog internally for quite a while (in relative terms). 'Digital' or 'analog' when talking about sensors refer to these internal workings, of which there is a lot in the sensor as a whole in addition to just the light sensitive pixels.


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## Andy Westwood (Feb 26, 2019)

I also watched this on You Tube not long after it was posted, being a studio photographer, I could never work out when I changed camera bodies (All Canon) I would get different exposures body to body using the exact lens and the same settings on my camera and lights.

This explains what could be the only reason for this, I'd never thought of this until I watched Tony's video on the subject, interesting but sad ISO can't be standardised across all cameras.

I like to nail my exposure in camera as much as possible, and it's easy to do that in a controlled environment such as a studio, but it would always take me a week or so using a different camera body, now I know Why!


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## Quarkcharmed (Feb 27, 2019)

magarity said:


> Because a CMOS device converts each pixel's output to digital immediately



Nope, it doesn't. More precisely it does in CMOS with so called digital pixels but they're not used in the cameras we compare here.


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## 3kramd5 (Feb 27, 2019)

magarity said:


> Because a CMOS device converts each pixel's output to digital immediately whereas a CCD keeps the pixels' signals analog internally for quite a while (in relative terms). 'Digital' or 'analog' when talking about sensors refer to these internal workings, of which there is a lot in the sensor as a whole in addition to just the light sensitive pixels.


They both generate charge from incident light. They use different means to convert that charge to potential, but both then digitize using ADC.


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## 3kramd5 (Feb 27, 2019)

knight427 said:


> Armature disclaimer (you get what you pay for):
> 
> 1- ISO in-variance still hits the wall of clipping. One you've filled your light bucket, there is no way to recover that information.



Right, but the point those who invented the term “ISO invariant” would make is: the noise is low enough that you can underexpose to prevent clipping highlights, and then selectively brighten only darker portions, recovering a wider range than the same image shot at a higher ISO but equivalent exposure.

Of course:
1) tonality suffers. Yes you can brighten more without noise becoming destructive as soon, but little detail is recorded. It looks flat.

2) returns are diminishing; noise is already fairly low. There is more to be gained by increasing well capacity, whether physically or computationally (e.g., modulo cameras).

3) none of the advantages apply if the scene doesn’t exceed the single exposure limitations.


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## epsiloneri (Feb 27, 2019)

I agree that the non-standard ISO numbers used by camera manufacturers are bad. Yes, "gain" would have been an appropriate label, but I can see the use of a standardised ISO - non-standardised ISO just gets confusing.

About the other point, that the ISO setting is just _digital_ gain, I highly doubt that as it would indeed be useless and only result in a loss of dynamic range. I've read about the tricks made by manufacturers to fake sub-stop ISO increases by adjusting the digital gain, but data (as shown by e.g. AlanF above) contradicts the ISO setting in general being a purely digital gain setting. I agree that the gain setting is of minor importance relative to other exposure decisions (focal length, aperture, and time) but to say that it is meaningless is just wrong.

Increasing the gain has two positive effects: improving the digital resolution of the signal, and reducing the relative importance of the (downstream) read-out noise. The downside is that the dynamic range is reduced, but as long as the detector is not saturated, nothing is lost by increasing the gain. That's why it makes sense to use the highest gain that doesn't saturate your exposure. You may not win much by increasing the gain to the saturation limit, but you don't loose anything either. Unless you intentionally want to overexpose or have good control over the lights, "auto-iso" therefore makes good sense.

If you're into extreme technical photography like astrophotography, there are other considerations that may restrict you (as characterising the detector becomes more important) but then you hopefully know what you're doing.


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## epsiloneri (Feb 27, 2019)

magarity said:


> Because a CMOS device converts each pixel's output to digital immediately whereas a CCD keeps the pixels' signals analog internally for quite a while (in relative terms). 'Digital' or 'analog' when talking about sensors refer to these internal workings, of which there is a lot in the sensor as a whole in addition to just the light sensitive pixels.


Perhaps you are referring to photon counting cameras, that can resolve single photon events? Neither CMOS nor CCDs are in general photon counters. CMOS and CCDs both record the photo-electric charge, but are read out differently. CCDs are read out by moving the charges row- or column-wise to the detector edge where they are A/D converted, while CMOS are A/D converted on site. This is the main reason why CMOS are so much faster at reading out.


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## hollybush (Feb 27, 2019)

bbb34 said:


> I wish camera manufacturers would call sensitivity and gain by their names, and use proper units.



Since the sensitivity is constant for a particular camera, it should live in the instruction manual. I'm happy with the combination (currently denoted "ISO") being the setting on the camera, because I want to use it with my flash meter or the Sunny 16 rule.



> And use a logarithmic scale instead of ridiculous large numbers.



It already exists, in the form of "DIN film speed", but has fallen out of use since the 1970s. DIN 21 = ISO 100, DIN 24 = ISO 200 etc. (it works like the dB scale).

Originally there was ASA (the American standard, Kodak) and DIN (the German standard, Agfa). When the international (ISO) standard was agreed, speeds were originally supposed to be written like this: "ISO 100/21°" and I remember film boxes came like that. Later on, only Agfa persisted with the dual numbers. I forget what Ilford (British) used.

Arguably a scale starting at 1 and proceeding in exact integers for stops might be more understandable, since no-one uses tables of logarithms base 10 any more, but the DIN numbers (if the ISO standard still permits them) would be a lot friendlier in the high ranges than the usual ISO scale.


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## Kit. (Feb 27, 2019)

epsiloneri said:


> Perhaps you are referring to photon counting cameras, that can resolve single photon events? Neither CMOS nor CCDs are in general photon counters. CMOS and CCDs both record the photo-electric charge, but are read out differently. CCDs are read out by moving the charges row- or column-wise to the detector edge where they are A/D converted, while CMOS are A/D converted on site. This is the main reason why CMOS are so much faster at reading out.


Not "A/D converted", but "converted to voltage range". A/D converters (which then convert a voltage value from this range to a binary code) are usually still one per row (or column), one per chip or even off-chip.


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## justaCanonuser (Feb 27, 2019)

knight427 said:


> Armature disclaimer (you get what you pay for):
> 
> 1- ISO in-variance still hits the wall of clipping. One you've filled your light bucket, there is no way to recover that information.


Digital & film shooter disclaimer: that's still a nice thing about negative film, it is much more forgiving in the highlights, there is no harsh clipping.


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## justaCanonuser (Feb 27, 2019)

I am not surprised about Tony Northrup's examples and conclusion. We have both a Canon and Nikon system, and noticed already several years ago that there is always a difference of 1/3 (or more) of a stop in the results of our Canon and Nikon digital cameras, using the same settings. Since Canon installed "Auto-ISO", I used that and stopped thinking about ISO when I shoot digital, I only think in the categories of less or more noise. 

I think ISO (if correctly implemented) made some sense in those days back when a lot of experienced photographers went digital, because it helped them to get a certain feeling for the digital work-flow. But that's over now, Tony N. is definitely right.


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## flip314 (Feb 27, 2019)

justaCanonuser said:


> Digital & film shooter disclaimer: that's still a nice thing about negative film, it is much more forgiving in the highlights, there is no harsh clipping.



I wish Canon had some way of protecting highlights better. On my 80D I almost always shoot at -2/3 exposure compensation because otherwise there's likely to be some area that blows out.

I can think of some ways to do it with extra features per pixel (for example one more and one less sensitive photodiode, or a ways to let excess charge spill over into a large capacitor), but they're likely to compromise the overall performance of the sensor due to the area they'd take up. It would also add to the processing burden, an area where Canon already seems weak.


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## rjbray01 (Feb 27, 2019)

LSXPhotog said:


> Thank you for speaking my mind. When I was first getting started in the publishing industry I knew a staff photographer just like him. That guy knew -or felt he knew- a lot about photography and would talk your ear off about it. We actually had a handful of good conversations about it over the years. However, he ultimately lost his job to me because he couldn't actually take photos with a camera. He just knew the technical aspects of it but editors would constantly complain about the images he delivered to them. (He had several...MANY reshoots over his tenure there.)
> 
> Focusing too much on the technical side of photography can't be fun. I have seen plenty of photos the Northrups share on their channel to know that they are _THAT_ guy I worked with. They know a lot about the technical side of photography - enough to be dangerous - but they may lack the creativity and ability to be successful photographers beyond the stock photography business they had.



Tony would probably be the first to agree with you ... he isn't selling himself as a great photographer .. he's in the "infotainment" industry ... and judging by his number of subscribers he seems to be doing pretty well at it !


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## Diko (Feb 27, 2019)

Both of them are right and wrong in the same time. Depending on the point of view.

What Tony does is to base his claims from the historical perspective of ISO. What current manufacturers do is on ISO 100 they stay with a base multiplication of electrons/photons count by zero (probably). On the other hand their tests are totally faulty. Neither of them did offered an image which would put to the test dynamic range which is as you know in correlation with the ISO. This actually is the most important aspect of this dispute.

In their tests both should have offered to the viewers deep shadows and drastic highlights and to check how much information is available after performing the tests with different settings.

I'm trying really very hard to imagine how would I find the difference between Canon 40D, Canon 5D4 or a CCD Hasselblad. You see, with the first and the last one you really are getting in dangerous territories with an ISO of 1600. Especially when looking for information from dark images. These days however with more recent models we know that this frontier has been crossed. And this is what it all counts for that in the end of the day I now that may be in a specific place by specific like conditions before I wasn't able to do and deliver what I can now.

Probably Tony could be right for one think they could have been talking to us with the gain which is a relative kind measuring because it's not the same again with different sensors In different camera setups. However from historical perspective even if the vendors would go the route where they would lower the ISO numbering that wouldn't help us to measure any advantage from the days before. The St. triangle wouldn't be a triangle anymore. It takes time and devotion to learn by heart (and I'm not speaking of understanding and knowing but feeling and getting used to like driving a car) the correct settings of manual photo shooting. You want to get rid of one part of it which from my current perspective would be much more confusing. But I don't know if I'm right because I am so used to it now.


REPLY


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## privatebydesign (Feb 28, 2019)

justaCanonuser said:


> Digital & film shooter disclaimer: that's still a nice thing about negative film, it is much more forgiving in the highlights, there is no harsh clipping.


Not really true. Once you over expose film it holds no detail it is just base emulsion and the dynamic range of all current digital cameras comfortably beats the dynamic range of even the best commonly available films. 

Now it is true that the exposure response curves of film don’t have the linear nature that digital captures do, but that is why a gamma curve is applied to every RAW image file, adjust that gamma curve and the highlight falloff is just the same as film. Digital did get a very bad reputation for blown highlights years ago because the dr was comparatively limited and it was very easy to not expose optimally for the medium, that is expose for the highlights which means most accurate exposures appear under exposed.


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## eosuser1234 (Feb 28, 2019)

It is technically eliminated when you put ISO to auto, and set your shutter speed and aperture to what ever you want in manual mode.


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## Kit. (Feb 28, 2019)

privatebydesign said:


> Not really true. Once you over expose film it holds no detail it is just base emulsion


For the negative, it's the other way around.



privatebydesign said:


> and the dynamic range of all current digital cameras comfortably beats the dynamic range of even the best commonly available films.


Actually, according to the data sheets, the dynamic range of Fuji's moderate-contrast negative film (Reala, NPC/NPH, 160C/400H) is about the same (if not better) as the DR of the 6D2/RP sensor.


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## privatebydesign (Feb 28, 2019)

Kit. said:


> For the negative, it's the other way around.
> 
> 
> Actually, according to the data sheets, the dynamic range of Fuji's moderate-contrast negative film (Reala, NPC/NPH, 160C/400H) is about the same (if not better) as the DR of the 6D2/RP sensor.


Sorry yes, I was thinking positive and negative film at the same time, I shot mostly slide film but I should have been more clear.

The 6D MkII and RP are probably the cameras with the lowest DR available today and the sensor is over 6 years old, whilst they are, I admit, “current digital cameras” I suppose I should have said current sensor technology.

Even so I think my points were valid. Digital used to have bad DR compared to film so got an undeserved reputation, especially in the highlights, because people didn’t expose it correctly. Digital and film have fundamentally different recording characteristics but if you understand what they are there is no effective advantage, technically, of one over the other. Digital cameras with modern specs have long outgrown the earlier generations of digital cameras and are every bit as capable, and generally better, of recording scenes as film was/is.

That does not mean I don’t believe film has value or a place in photography, it also doesn’t mean using film cameras doesn’t have a certain style and feel that can infuse itself into the final image.


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## mikemilton (Feb 28, 2019)

I'm mainly inteested in cinematography. In the C-series cameras, Canon has documented (in their whitepapers) that there is analog gain applied (prior to raw recording) that varies with ISO setting. That gain is .5x below 850ISO (C300) and rises above that setting. So, for these cameras (and I assume others) ISO is 'real' in the sense that it materially changes what is recorded in a way that cannot be changed in post processing. 

This point is usually discussed in relationship to stops above and below middle gray (and DR) that are recordable at various ISO settings. In other words, the concrete impact ISO has on results.


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## tallrob (Feb 28, 2019)

Sure, you could debunk any standard of measurement you want by the same methods. The kilopascal (kpa) is totally fake because it's different at one elevation than it is at another. Mph is fake because it's relevant to the speed of other moving objects. A pound only weighs a pound in a vacuum. 

ISO is a measurement of light sensitivity and/or gain. Just because some camera's light meters are bad doesn't make it less relevant. Why do people try to get attention by convincing stupid people they can debunk traditional photography standards? Oh yeah, page hits fuel ad revenue. Bingo.


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## tallrob (Feb 28, 2019)

Mt Spokane Photography said:


> Yes, and film was also marketed with higher ISO ratings, but was the same exact film but with longer processing times. A similar bunch of comments were made.



But it told the lab what setting was used, and therefore how long to process it. Totally necessary.


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## 3kramd5 (Feb 28, 2019)

bbb34 said:


> I wish camera manufacturers would call sensitivity and gain by their names, and use proper units. And use a logarithmic scale instead of ridiculous large numbers.



The intent of the ISO standard governing digital camera speed ratings is to harmonize digital with film. I suppose camera makers could put a gain control knob in dB on cameras, but the ISO paradigm is well understood and established.


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## justaCanonuser (Feb 28, 2019)

privatebydesign said:


> Sorry yes, I was thinking positive and negative film at the same time, I shot mostly slide film but I should have been more clear.


I didn't mean positive (slide) film, such a film isn't very forgiving and needs careful metering, of course. But in particular many negative b&w films have a lot of latitude in the highlights. I know what I am speaking about, because I still shoot and develop films by myself, aside digital photography.


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## Don Haines (Feb 28, 2019)

It is an approximation. It is a scale that compares a digital interpretation of an analog reading of a photo-electronic phenomenon to that of chemical processing of a photo-chemical reaction that is time and temperature sensitive, where both sides of the comparison are rounded to a set of standard numbers.

Anyone looking for exact results will be sorely disappointed. You are comparing something that is somewhat close to X (within about 50percent) against something that is somewhat close to Y (also within about 50 percent) and getting upset that they are not the same.


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## AJ (Feb 28, 2019)

3kramd5 said:


> I suppose camera makers could put a gain control knob in dB on cameras, but the ISO paradigm is well understood and established.


I want that. I want one that goes to 11. Because 11 is louder than 10.


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## Don Haines (Feb 28, 2019)

AJ said:


> I want that. I want one that goes to 11. Because 11 is louder than 10.


Interesting..... I think most Canon FF cameras alread go up to 33


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## 3kramd5 (Feb 28, 2019)

AJ said:


> I want that. I want one that goes to 11. Because 11 is louder than 10.


But it’s a digital camera, so 11 is only three.


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## epsiloneri (Mar 1, 2019)

Kit. said:


> Not "A/D converted", but "converted to voltage range". A/D converters (which then convert a voltage value from this range to a binary code) are usually still one per row (or column), one per chip or even off-chip.


Yes, thanks for the correction. Each pixel is readout with its own amplifier, with typically one or two ADC per column/row. Per-pixl ADC are still experimental.


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## 3kramd5 (Mar 1, 2019)

epsiloneri said:


> Yes, thanks for the correction. Each pixel is readout with its own amplifier, with typically one or two ADC per column/row. Per-pixl ADC are still experimental.


Per pixel amplifier? Do you have a schematic for that?


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## AlanF (Mar 1, 2019)

There has been a lot of hot air about the inconsistency of iso among manufacturers. There is real evidence, however, to the opposite. DxOMark has been measuring for years the actual iso values for tested sensors and plotting them against the stated ones. There is in fact a remarkable consistency among the top makers I have looked at, and a consistent pattern of deviations of the manufacturers stated from the actual, as seen in these two comparisons. Such remarkable agreement among these manufacturers suggest they are attempting to conform to the standards of ISO, and maybe even their tabulated values might be correct and there are systematic errors in DxOMark's measurements (figures courtesy of DxOMark).


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## Kit. (Mar 1, 2019)

3kramd5 said:


> Per pixel amplifier? Do you have a schematic for that?


Wikipedia has.

If sensor readout speed and pixel charge capability are not a problem to your case, a CCD with a single amplifier is more consistent in results.


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## Michael Clark (Mar 1, 2019)

AlanF said:


> There has been a lot of hot air about the inconsistency of iso among manufacturers. There is real evidence, however, to the opposite. DxOMark has been measuring for years the actual iso values for tested sensors and plotting them against the stated ones. There is in fact a remarkable consistency among the top makers I have looked at, and a consistent pattern of deviations of the manufacturers stated from the actual, as seen in these two comparisons. Such remarkable agreement among these manufacturers suggest they are attempting to conform to the standards of ISO, and maybe even their tabulated values might be correct and there are systematic errors in DxOMark's measurements (figures courtesy of DxOMark).
> 
> View attachment 183356
> View attachment 183357



Digital cameras tend to overstate the ISO. What they call ISO 400 is really more like ISO 250-320. Film was often the opposite: what was actually sensitive at around ASA 80 would be sold as ASA 64. Of course, as film ages the sensitivity goes down, so that ASA 64 that was actually ASA 80 when it was factory fresh might only be ASA 72, or even ASA 64 by the expiration date.


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## AlanF (Mar 1, 2019)

Michael Clark said:


> Digital cameras tend to overstate the ISO. What they call ISO 400 is really more like ISO 250-320. Film was often the opposite: what was actually sensitive at around ASA 80 would be sold as ASA 64. Of course, as film ages the sensitivity goes down, so that ASA 64 that was actually ASA 80 when it was factory fresh might only be ASA 72, or even ASA 64 by the expiration date.


The DxOMark data do consistently show that the makers consistently overstate the isos above 100, and understate at iso 50. DxO explains this in https://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity where the detail the measuring of iso values. They say manufacturers deliberately overstate the iso to avoid clipping of highlights. But, something smells when different manufacturers have exactly the same deviations from the DxO measurements. Do you know of any other independant measurements?


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## 3kramd5 (Mar 1, 2019)

Michael Clark said:


> Digital cameras tend to overstate the ISO. What they call ISO 400 is really more like ISO 250-320.


They are supposed to round up to the nearest 1/3 stop. 321 should be reported as 400. 250 to 400 breaks both the ISO and the industry standard. I wonder if amateur comparisons are done consistency with proper conditions.


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## Kit. (Mar 1, 2019)

AlanF said:


> The DxOMark data do consistently show that the makers consistently overstate the isos above 100, and understate at iso 50. DxO explains this in https://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity where the detail the measuring of iso values. They say manufacturers deliberately overstate the iso to avoid clipping of highlights. But, something smells when different manufacturers have exactly the same deviations from the DxO measurements. Do you know of any other independant measurements?


What bothers me is that in their "testing protocol" (https://www.dxomark.com/About/In-depth-measurements/DxOMark-testing-protocols/ISO-sensitivity) they don't specify the color temperature of their light source and even do explicitly mention LEDs. And _then_ they also don't say what they do if the saturation of the different color channels happens at different exposures.


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## hollybush (Mar 1, 2019)

AlanF said:


> Such remarkable agreement among these manufacturers suggest they are attempting to conform to the standards of ISO,



One would hope so, otherwise a flash meter wouldn't be much use.


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## knight427 (Mar 1, 2019)

3kramd5 said:


> But it’s a digital camera, so 11 is only three.



There are only 10 types of people, those who understand binary, and those who don’t.


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## Don Haines (Mar 1, 2019)

knight427 said:


> There are only 10 types of people, those who understand binary, and those who don’t.


I was shooting today at ISO 11001000000000, way better than 11......


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## flip314 (Mar 1, 2019)

I wonder what made Nikon stop at 3.2 million ISO. I want to be able to shoot at ISO 4 billion, even if there's literally zero dynamic range.


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## Click (Mar 2, 2019)

knight427 said:


> There are only 10 types of people, those who understand binary, and those who don’t.





Don Haines said:


> I was shooting today at ISO 11001000000000, way better than 11......



LOL


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## Berowne (Mar 3, 2019)

epsiloneri said:


> Perhaps you are referring to photon counting cameras, that can resolve single photon events? Neither CMOS nor CCDs are in general photon counters. CMOS and CCDs both record the photo-electric charge, but are read out differently. CCDs are read out by moving the charges row- or column-wise to the detector edge where they are A/D converted, while CMOS are A/D converted on site. This is the main reason why CMOS are so much faster at reading out.



"CMOS and CCDs both record the photo-electric charge" - so this is the reason why they are called analog devices? Because charge is a continuous value, not a discrete one (0 or 1).


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## Kit. (Mar 3, 2019)

Berowne said:


> "CMOS and CCDs both record the photo-electric charge" - so this is the reason why they are called analog devices? Because charge is a continuous value, not a discrete one (0 or 1).


As we can disregard number-phase uncertanty for photoelectrons, charge is a discrete value (a number of electrons). But counting electrons one by one is too slow for our goals, so the charge is measured by the voltage it creates on a given capacitor, and voltage is a continuous value.


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## Berowne (Mar 3, 2019)

Kit. said:


> What bothers me is that in their "testing protocol" (https://www.dxomark.com/About/In-depth-measurements/DxOMark-testing-protocols/ISO-sensitivity) they don't specify the color temperature of their light source and even do explicitly mention LEDs. And _then_ they also don't say what they do if the saturation of the different color channels happens at different exposures.



Kit, if i remember well, the exposure meter is sensitive to different colours (measures different values for different colours), but not the sensor. Anyway, if you take photos of a grey-card (18%), this should not matter at all.


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## Kit. (Mar 3, 2019)

Berowne said:


> Kit, if i remember well, the exposure meter is sensitive to different colours (measures different values for different colours), but not the sensor. Anyway, if you take photos of a grey-card (18%), this should not matter at all.


The sensor has 3 color channels saturating with some degree of independence: the ones corresponding to R, G, and B color filters of its Bayer pattern. You don't just "take photos of a grey card", you take photos of a grey card that is illuminated by light of a particular spectrum. If it's a bluish light (high color temperature), the B channel would normally saturate at a lower exposure (and the R channel would normally saturate at a higher exposure) than if it were a reddish light (low color temperature). If it's a LED light, with spectrum vastly different from the spectrum of an incandescent source, both the R and the B channels can saturate before the G channel does.


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## TAF (Mar 3, 2019)

If you know your skills as well as your equipment, you will be successful in a thousand photographs.
If you know your skills but not your equipment, for every successful photograph, there will be a failure.
If you know neither your skills nor your equipment, use the green box setting...

with apologies to Sun Tzu


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## Pape (Mar 3, 2019)

you dont need know how wheel works to drive with bicycle. Just jump to saddle and have fun 
same goes with ISO i believe ? were it fake or not it reduces post editing job


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## TAF (Mar 3, 2019)

Perhaps I am simply old (yet not even 60), but doesn't everyone use an 18% gray card and evaluate their new toy equipment to make certain they know how it really works before getting serious?

In the days of film, when I bought a new type of film, I would put a few 'known exposure' frames at the head of the roll and then follow the manufacturers instructions precisely, so that I would know how far it deviated from my expectations. I could then make appropriate adjustments, and I was all set. Since the film makers were VERY consistent within their own product, I rarely noticed any changes once I knew where I was.

But KODAK to Agfa to Fuji etc? And then within film types? Plenty of differences to account for.

At least our modern sensors don't change over time, at least not that I have noticed. Has anyone with a really early camera noticed any changes? We are exposing a silicon surface to light, which does cause changes on the microscopic level. And of course, the shutter could need eventually adjustment, but I haven't had a digital SLR that hasn't warranted upgrading within a short enough period of time (under 10 years so far) such that perhaps there isn't time for deterioration to set in.


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## Don Haines (Mar 3, 2019)

TAF said:


> Perhaps I am simply old (yet not even 60), but doesn't everyone use an 18% gray card and evaluate their new toy equipment to make certain they know how it really works before getting serious?
> 
> In the days of film, when I bought a new type of film, I would put a few 'known exposure' frames at the head of the roll and then follow the manufacturers instructions precisely, so that I would know how far it deviated from my expectations. I could then make appropriate adjustments, and I was all set.


HA!

You have no idea how many pictures I have of my Kodak colour card! 

Shooting in RAW and the ability to adjust white balance in post (at least to me) has to be the greatest leap forward in shooting with digital.......


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## BeenThere (Mar 3, 2019)

Don Haines said:


> HA!
> 
> You have no idea how many pictures I have of my Kodak colour card!
> 
> Shooting in RAW and the ability to adjust white balance in post (at least to me) has to be the greatest leap forward in shooting with digital.......


Certainly one of the greatest. For me, instant gratification (not having to wait for film developing) would have to be the greatest leap forward of digital photography.


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## Click (Mar 3, 2019)

BeenThere said:


> For me, instant gratification (not having to wait for film developing) would have to be the greatest leap forward of digital photography.



+1 

I totally agree with you.


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## stevelee (Mar 3, 2019)

Click said:


> +1
> 
> I totally agree with you.


I sort of agree. I enjoyed the anticipation waiting a few days for my slides to come in the mail to see my results. I perhaps also could look at the pictures with more objectivity than in the moment.

Now I have a short time of anticipation (except when traveling), the wait between shooting and popping the card into the computer and seeing how the pictures look in Bridge and then in ACR. Looking at pictures on the camera's screen is just a preview. On a long trip, I have looked at pictures on the iPad via Canon software and a wifi connection.


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## Michael Clark (Mar 4, 2019)

3kramd5 said:


> They are supposed to round up to the nearest 1/3 stop. 321 should be reported as 400. 250 to 400 breaks both the ISO and the industry standard. I wonder if amateur comparisons are done consistency with proper conditions.



I don't think anyone would consider DxO Lab's setup "amateur." They are a bit secretive about their methodology and weighting for the composite scores they give cameras and lenses, but the actual measurements they publish are done under properly controlled conditions.


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## Michael Clark (Mar 4, 2019)

Berowne said:


> "CMOS and CCDs both record the photo-electric charge" - so this is the reason why they are called analog devices? Because charge is a continuous value, not a discrete one (0 or 1).



The sensors in digital cameras are analog devices. That's why the analog measurements they make require an _analog-to-digital convertor (ADC) _somewhere between the sensels (a/k/a pixel wells, photosites, etc.) and the digital processor.



Kit. said:


> As we can disregard number-phase uncertainty for photoelectrons, charge is a discrete value (a number of electrons). But counting electrons one by one is too slow for our goals, so the charge is measured by the voltage it creates on a given capacitor, and voltage is a continuous value.



Not really. The exact amount of energy a photon contains varies with the frequency at which it is oscillating. There's no way to measure discrete photons by using the amount of energy absorbed by a piece of silicon, there is only the measurement of the energy that has been released by those photons.



Berowne said:


> Kit, if i remember well, the exposure meter is sensitive to different colours (measures different values for different colours), but not the sensor. Anyway, if you take photos of a grey-card (18%), this should not matter at all.



That all depends on the exposure meter. Many are monochrome. Just as the earliest emulsions were more sensitive to blue light (and pretty much not sensitive to green-yellow-orange-red light), the earliest light meters were sensitive to the same wavelengths as the current emulsions were. Many current digital cameras have RGB+IR sensitive light meters (DSLRs) if they're not metering directly off the image sensor (MILCs).



TAF said:


> At least our modern sensors don't change over time, at least not that I have noticed. Has anyone with a really early camera noticed any changes? We are exposing a silicon surface to light, which does cause changes on the microscopic level. And of course, the shutter could need eventually adjustment, but I haven't had a digital SLR that hasn't warranted upgrading within a short enough period of time (under 10 years so far) such that perhaps there isn't time for deterioration to set in.



Theoretically, the biggest difference would be caused by the Bayer color array fading from exposure to UV, but since the Bayer mask is usually behind the UV filter in the sensor stack, it would take a LOT of exposure to direct sunlight or other sources of UV for this to happen.




BeenThere said:


> Certainly one of the greatest. For me, instant gratification (not having to wait for film developing) would have to be the greatest leap forward of digital photography.



That and the automatic recording of EXIF data without having to stop and write everything down so you can later tell what did, and perhaps more importantly what didn't, work.


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## Kit. (Mar 4, 2019)

Michael Clark said:


> Not really. The exact amount of energy a photon contains varies with the frequency at which it is oscillating. There's no way to measure discrete photons by using the amount of energy absorbed by a piece of silicon, there is only the measurement of the energy that has been released by those photons.


The sensor does _not_ measure the energy the absorbed photons release. Most of this energy (for silicon sensors used in photography) is converted into _phonons_ and thus lost with heat.

The sensor measures the number of electrons the absorbed photons excite. Which is usually one per photon, as multi-electron absorption of a photon is a process happening with much lower probability.


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## 3kramd5 (Mar 4, 2019)

Michael Clark said:


> I don't think anyone would consider DxO Lab's setup "amateur." They are a bit secretive about their methodology and weighting for the composite scores they give cameras and lenses, but the actual measurements they publish are done under properly controlled conditions.


I wasn’t referring to anyone in particular with that comment, merely recognizing that there are myriad outfits offering free test results. Some are undoubtedly better than others when it comes to controls, consistency, and adherence to standards. I could see, for example, some website deciding to round to the nearest 1/3 stop, rather than up as per standard, leading to discrepancies appearing larger.


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## Michael Clark (Mar 4, 2019)

AlanF said:


> The DxOMark data do consistently show that the makers consistently overstate the isos above 100, and understate at iso 50. DxO explains this in https://www.dxomark.com/About/In-depth-measurements/Measurements/ISO-sensitivity where the detail the measuring of iso values. They say manufacturers deliberately overstate the iso to avoid clipping of highlights. But, something smells when different manufacturers have exactly the same deviations from the DxO measurements. Do you know of any other independant measurements?



I've seen quite a few other sources that even measure the 1/3 stop setting (which can be _very_ revealing about how different cameras handle ISO settings between the "whole stop" scale!). They all show the same thing.

This one actually compares their measurements to DxO:

http://www.photonstophotos.net/Charts/Measured_ISO.htm#Canon%20EOS%201DX%20Mark%20II,Nikon%20D5,Pentax%20K-1 

There is a lot of validity to the highlight preservation thing. Digital sensors have linear response all the way up to full saturation (clipping). Film is different because as the chemicals in the emulsion react to light, there are fewer unaltered grains left to react to even more light. The reduced ISO sensitivity of digital sensors is only apparent when measuring raw values. The camera's internal processor and external raw processing applications know to "push" the exposure (after gamma curves have been applied to give the highlight response a "shoulder") when converting the raw data to counteract the "pull" of exposing for ISO 400 when the data from the sensor is only being amplified equivalent to ISO 250-300. That's one of several reasons why raw processing applications must have codecs for specific cameras before they can process raw image files from a specific camera: to know specifically for each sensor how much the "push" needs to be at each ISO setting.


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## Michael Clark (Mar 4, 2019)

Kit. said:


> The sensor does _not_ measure the energy the absorbed photons release. Most of this energy (for silicon sensors used in photography) is converted into _phonons_ and thus lost with heat.
> 
> The sensor measures the number of electrons the absorbed photons excite. Which is usually one per photon, as multi-electron absorption of a photon is a process happening with much lower probability.



You are, of course, correct with your more precise description of how photons colliding with a silicon sensor excites electrons. I was trying to keep it simple. But the fact remains, as long as the possibility/probability of multi-electron absorption is there, we can't with 100% confidence say that one electron = one photon. That's an even more oversimplified description than my original comment above.


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## AlanF (Mar 4, 2019)

Michael Clark said:


> I've seen quite a few other sources that even measure the 1/3 stop setting (which can be _very_ revealing about how different cameras handle ISO settings between the "whole stop" scale!). They all show the same thing.
> 
> This one actually compares their measurements to DxO:
> 
> ...


Michael
Thank you. But, photonstophotos is a site I had consulted and replotted data from it in this thread, and the site doesn't say why the DxO measurements differ, merely that they are different.


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## Michael Clark (Mar 4, 2019)

AlanF said:


> Michael
> Thank you. But, photonstophotos is a site I had consulted and replotted data from it in this thread, and the site doesn't say why the DxO measurements differ, merely that they are different.



I've also seen talk by coders who look at the codecs of various camera's plugins for darktable or rawtherapee and determine how much the "push" is for each camera at each ISO setting when converting the raw data. It's a very real thing.


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## TAF (Mar 6, 2019)

BeenThere said:


> Certainly one of the greatest. For me, instant gratification (not having to wait for film developing) would have to be the greatest leap forward of digital photography.



Not only the instant gratification, but the cost savings! I've taken 10x as many photos since getting digital (on an annual basis) as I did with film. Since the 'keeper' rate is about the same, that means I have many more photos I really like than I used to get.

I've also captured things I would never have considered before, since I hated to waste film - one might need that frame for something really important later.

And of course there is the 'essentially no limit' to how many shots in a sequence. 36 frames always seemed limiting (and yes, I used those rare 72 frame rolls, and I even had a 250 frame film back for my Canon F-1 - hated that thing, it was so unwieldy)

We are indeed in the golden age of photography.


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## stevelee (Mar 6, 2019)

It was good for me to have spent years shooting color slides. Everything had to be right. There was a group of classmates in college who insisted on viewing my roll of slides when they came in, before I had seen them or edited anything out. They were both fans of my work and merciless critics. It inspired a level of discipline when I was shooting and a good education.

And money was a factor, of course, especially while I was still in school.


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## Khristo (Mar 11, 2019)

So I played with this a bit yesterday. Set up my 5D3 with a highly contrasty scene - inside looking from darker room areas out to bright blue sky and fluffy white clouds. Set a middling manual exposure of aperture and shutter (can't remember exactly what, but say f8 and 60th), then took seven shots in 1 stop increments from 100 ISO through to 3200 ISO, all without changing the manual exposure settings. 
Processed RAW images in Lightroom. Without any processing on import, the 100 ISO was very dark, while the 3200 was very bright. Then adjusted the exposure in LR (+3.0 stops for the 100 ISO, +2 stops for the 200 ISO, and so on to -3.0 for the 3200 ISO).
If the whole system (sensor, plus in-camera processing, plus LR processing) was ISO invariant, each image should have looked the same? Well they sure didn't. 
The 100 ISO shot had MASSIVE noise in the pushed dark areas while the 1600 and 3200 ISO shots were not noisy in that area. The sky areas in the 100 ISO shot were nice blue sky and fluffy cloud detail. Same areas in the 3200 ISO shot was totally blown white, and almost as much in the 1600 shot. (White balance was also different at the same colour temp setting.)

After reading this thread and some other info, I had expected to see much less difference. And that would have made sense from the idea that the physical sensor's light gathering capability can't change based on what ISO you dial in. In fact, having seen the results of my simple test, I'm now wondering what the hell is going on in-camera to get this difference - even wondering if the camera can evaluate the scene, compare with your Av Tv and ISO settings and maybe adjust the settings a bit (without telling you or your RAW file) on the basis of an assumption of what you're trying to achieve. Seems unlikely, but I really am sceptical that such a difference would be evident just from the difference between the analogue and digital amplification steps.

Anyway, upshot is, if you got a 5D3, don't think you can set any 'ol number on the ISO dial and fix it later. Not quite sure how, but there's a big difference.


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## AlanF (Mar 11, 2019)

You missed some key points in the thread. Firstly, the 5DIII doesn’t reach isoinvariance until about iso640 and its DR is relatively flat between 100-640 so pushing dark areas at iso100 is bound to be noisy. Secondly, setting the iso sets-where you begin to clip the highlights so if you have too high an iso you will blow the highlights. What the discussion should have told you is that if your iso setting is in the isoinvariant region then setting too low an iso in RAW, ie you are under exposing, the underexposure can be corrected over quite a range in post processing and you end up withe same noise and DR as you would have had if you had set the “correct” higher iso. For example, if the correct settings should be iso3200 and 1/200s, then setting manually iso1600 and 1/200 and increasing exposure by 1ev or setting at iso800 and 1/200s and increasing by 2ev in Photoshop etc should give very similar DR and noise to what you would have had at iso3200. You can’t do it the other way around by overexposing and decreasing exposure in post.


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## Michael Clark (Mar 11, 2019)

Khristo said:


> So I played with this a bit yesterday. Set up my 5D3 with a highly contrasty scene - inside looking from darker room areas out to bright blue sky and fluffy white clouds. Set a middling manual exposure of aperture and shutter (can't remember exactly what, but say f8 and 60th), then took seven shots in 1 stop increments from 100 ISO through to 3200 ISO, all without changing the manual exposure settings.
> Processed RAW images in Lightroom. Without any processing on import, the 100 ISO was very dark, while the 3200 was very bright. Then adjusted the exposure in LR (+3.0 stops for the 100 ISO, +2 stops for the 200 ISO, and so on to -3.0 for the 3200 ISO).
> If the whole system (sensor, plus in-camera processing, plus LR processing) was ISO invariant, each image should have looked the same? Well they sure didn't.
> The 100 ISO shot had MASSIVE noise in the pushed dark areas while the 1600 and 3200 ISO shots were not noisy in that area. The sky areas in the 100 ISO shot were nice blue sky and fluffy cloud detail. Same areas in the 3200 ISO shot was totally blown white, and almost as much in the 1600 shot. (White balance was also different at the same colour temp setting.)
> ...



The difference is that dynamic range is always relative, never absolute. It's saying the same thing in a different way as when we say "noise": what we really mean is the Signal-to-Noise Ratio. You can have three times as much noise in an image, but if you have nine times the signal (and have not blown the highlights) then you have a cleaner image.

When you underexpose by three stops at ISO 100, you're packing all of the dynamic range of the scene into the lowest 8th of the camera's dynamic range without reducing the camera's fixed pattern and read noise. When you overexpose by three stops, you're placing all of the camera's dynamic range in the dimmest parts of the scene.


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