# Advice on a upgrade from the Rebel XS



## tevscale (May 11, 2014)

Let me start by explaining my situation: I'm relatively new to photography (have been using a DSLR for about 2 years) and primarily shoot my kids at their various activities and outdoor/nature scenes (with a preference for individual plants or animals rather than landscapes). 

My current equipment consists of a Rebel XS with 18-55 EF-S kit lens, 50mm 1/8, 80-200 2.8 L, and 430 EX II flash. For well over 90% of what I want to do, this is just fine, and has provided some shots that I'll treasure for the rest of my life (most of the shots I miss are due to me, not the gear). But remaining few % is irritating! Most of my problems are in low light (indoor event for the kids where flash isn't allowed or I'm too far away to use it) where I could benefit from better high ISO performance than the Rebel can offer. The other issue is catching the "key moment" when action is occurring, where the Rebel's frame rate isn't up to the task (I shoot RAW since I don't think the JPEGs from the Rebel are particularly good, and that reduces the frame rate to about 1-2Hz).

I'm aware that a 5D III would fix all my problems. But that's expensive, made more so by the need for a replacement for my EF-S lens. So I'd like opinions on the more budget-friendly options, in order:

7D or 70D: these are fast enough, but do they do well enough in low light? I'll define "well enough" as having at least the same image quality at ISO 3200 as the Rebel does at 800.

6D: fixes the low-light issues, but is the frame rate fast enough to have a decent shot at capturing action?

I'd appreciate any advice on this. Should I go for one of the above options, or just bide my time and save up for the 5D III?


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## ajfotofilmagem (May 11, 2014)

Unfortunately, there is currently a camera that is much better than a Rebel XS, both in low light and in fast action. The Canon 7D has been superseded by the 70D in high ISO performance, but not enough to ISO 3200 looks like 800 of your old Rebel. In fact, there is no APS-C camera has achieved this level of performance.

Canon 6D will show improvement in high ISO you want, but do not get too many pictures per second, perfectly focused. The focus points are not very sensitive and efficient, with the exception of the central point. 

Remember that to achieve the potential quality of 6D, you will need modern high quality lenses that cost more than the 6D own. 
The 70D has the option kit with 18-55 lens STM great, which makes it quick and silent focus, and is a significant upgrade over your old XS.


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## Mt Spokane Photography (May 11, 2014)

tevscale said:


> primarily shoot my kids at their various activities and outdoor/nature scenes (with a preference for individual plants or animals rather than landscapes).
> 
> My current equipment consists of a Rebel XS with 18-55 EF-S kit lens, 50mm 1/8, 80-200 2.8 L, and 430 EX II flash. For well over 90% of what I want to do, this is just fine, and has provided some shots that I'll treasure for the rest of my life (most of the shots I miss are due to me, not the gear). But remaining few % is irritating! Most of my problems are in low light (indoor event for the kids where flash isn't allowed or I'm too far away to use it) where I could benefit from better high ISO performance than the Rebel can offer. The other issue is catching the "key moment" when action is occurring, where the Rebel's frame rate isn't up to the task (I shoot RAW since I don't think the JPEGs from the Rebel are particularly good, and that reduces the frame rate to about 1-2Hz).
> 
> Should I go for one of the above options, or just bide my time and save up for the 5D III?


 
Since you are using raw right now, the sensors on the 70D and 7D are not much more capable if any than what you have. You gain features and faster processors and video features.

Have you considered a 6D? Its in the same price range as a 70D, and you can get a refurb right now for $1300.

You will get low light capability, and better extreme low light AF than the 5D MK III.

I'm not a fan of machine gunning thousands of frames just to get the right moment, I find its possible 99% of the time with one shot, and I do not have time to sort thru thousands of raw images looking for the best of the best. I've done it with my 1D MK IV, and its no fun.

I currently have a 5D MK III, its wonderful, but I'd be very happy with a 6D as well, I virtually never use fast frame rates unless its a very unusual circumstance, like trying to capture a arrow in flight, the tip of a bull whip when it snaps the object out of the holders fingers. It could also be useful for a BIF, but even there, I use one shot.

There are lots of good choices, and each has benefits and drawbacks.

If you upgrade your glass, that will stay with you thru generations of bodies.

A 135mm f/2L is fantastic for low light when you are away from the subject. A 85mm f/1.8 will also capture low light images that are a bit further away than the 50mm can handle.

Which lens do you use most? A 17-55mm IS will replace the 18-55 and be worlds better. A 15-85mm will give more flexability, and will also be a big improvement.

Try borrowing or renting a 6D and a 70D (Pass on the 7D, its not very good in low light). Try them both a ISO 25600.

The bottom line is that you pay a lot of $$ for a incremental improvement in the APS-C line, which is why jumping to a 6D may be attractive for low light use, and almost everything else.


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## sagittariansrock (May 11, 2014)

tevscale said:


> Let me start by explaining my situation: I'm relatively new to photography (have been using a DSLR for about 2 years) and primarily shoot my kids at their various activities and outdoor/nature scenes (with a preference for individual plants or animals rather than landscapes).
> 
> My current equipment consists of a Rebel XS with 18-55 EF-S kit lens, 50mm 1/8, 80-200 2.8 L, and 430 EX II flash. For well over 90% of what I want to do, this is just fine, and has provided some shots that I'll treasure for the rest of my life (most of the shots I miss are due to me, not the gear). But remaining few % is irritating! Most of my problems are in low light (indoor event for the kids where flash isn't allowed or I'm too far away to use it) where I could benefit from better high ISO performance than the Rebel can offer. The other issue is catching the "key moment" when action is occurring, where the Rebel's frame rate isn't up to the task (I shoot RAW since I don't think the JPEGs from the Rebel are particularly good, and that reduces the frame rate to about 1-2Hz).
> 
> ...



I think you will do yourself a favor by switching to faster lenses for now. A f/1.4 lens will make more difference to your images than a switch to 7D or 70D, IMO.


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## jrista (May 11, 2014)

tevscale said:


> 7D or 70D: these are fast enough, but do they do well enough in low light? I'll define "well enough" as having at least the same image quality at ISO 3200 as the Rebel does at 800.
> 
> 6D: fixes the low-light issues, but is the frame rate fast enough to have a decent shot at capturing action?
> 
> I'd appreciate any advice on this. Should I go for one of the above options, or just bide my time and save up for the 5D III?



Fundamentally, ISO/noise performance is a factor of two things: Real sensitivity (quantum efficiency) and *total *sensor area. Assuming you frame your subject the same, the only way to really reduce noise is to use a larger sensor. Pixel size does not really play a role unless your only putting the same number of pixels on the subject (which means you are not necessarily framing the same). With the same number of pixels on subject, then pixel size matters, and larger pixels do better. 

Given these facts, it's highly unlikely that you will ever see an APS-C camera that has ISO 800-level performance at ISO 3200. Even if Q.E. reached 100%, your still not going to see that much of an improvement. I think the XS had around 25-30% Q.E. The 7D has 41% and the 70D has 45%. That is not even a factor of two improvement over the XS, let alone a factor of four improvement. You will see an improvement in high ISO IQ, but no where near enough that ISO 3200 looked like ISO 800. ISO 1600 will look a lot better, almost as good as ISO 800 on your XS, but still not quite as good. 

The only real way you are going to get a significant improvement in high ISO performance is to move up to a full-frame camera. The 6D has about 50% Q.E., so just from a real sensitivity standpoint, it's about twice as sensitive as your XS. On top of that, it's got 2.6 times the sensor area. So you'll gain almost two stops of improvement in high ISO performance...indeed, ISO 3200 would look a lot like ISO 800 on your XS. Because of the greater pixel count, if you frame the same, ISO 3200 should look quite a bit better than ISO 800 on your XS for a given output size. These same fundamental facts apply to the 5D III as well. It has 49% Q.E. and the same total sensor area.

Whether you choose the 6D or 5D III is really up to you. The AF performance is indeed much superior on the 5D III, and for action, that will certainly be better. The 6D's 11pt AF system is not bad, though, and at least for kids and for some lower action wildlife, it should suffice quite nicely. The 5D III's AF system is going to be able to lock onto active subjects, like kids running around or wildlife in action, a lot better than the 6D's. For action, frame rate is pretty important as well, and I'm not sure the 4.5fps of the 6D is really quite up to snuff. Personally, my limit, having used 3.4fps, 3.7fps, 6fps and 8fps cameras, is about 6fps. Anything lower than that, and I really feel I'm missing the right moments. At 8fps the frame rate feels really good, and you definitely see an improvement in small changes in subject pose and orientation that give you the option of picking a really ideal frame. The 7D, which I own, has an AF jitter problem that causes some frames to become very slightly out of focus, which basically negates some frames for all but the smallest reproduction ratio online. My average "keeper rate" is about 5-6fps at best, which is part of the reason I feel the 6fps of the 5D III, with it's much better AF system, is acceptable for action. I say acceptable, however ideally I'd say 8-20fps is probably where the sweet spot is, and I think 10-12fps, maybe 15fps is really quite ideal (assuming the AF system can keep up.)

At the very least, given that you've stated high ISO performance is one of your biggest concerns, that you should really move up to a full frame camera. The 6D is a very nice camera, and for certain applications, like landscapes, low light photography, and still scenes (like floral macros), and even astrophotography, it is a very, very good camera. For action, it's maybe middle ground at best. The AF system is capable enough, but the 4.5fps frame rate may just not quite be up to snuff. Whether you choose the 5D III or not would really have to be up to you. If you do choose the 6D, I honestly think you will find it to be a truly MASSIVE improvement over your XS...despite the shortcomings of the 6D vs. the 5D III, it really is a vastly superior device compared to your XS, and once you get it in your hands, you'll understand what I mean.


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## jdramirez (May 11, 2014)

I have a 5d mkiii and when I had the xs I would spray and pray.

Now that I have the mkiii... I time the action and I depress when it is time to take the shot... then I hold a few extra beats and then look after.

I'd suggest a 6d for improved low light, use the center point, crop in post, and then time and blast... your results should be more than adequate.

While the 7d and 70 will be fine... full frame is the better choice...


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## tevscale (May 13, 2014)

Thanks to all who took the time to respond! The detailed information is extremely helpful. It looks like the 6D with 24-105 kit lens (to replace the field of view range of my 18-55 EF-S), and upgrading my 50mm to an f/1.4 would meet essentially all my needs. Of course that opens the door to the Sigma vs. Canon debate regarding the 50mm f/1.4, but I'm thinking that the Canon would be good enough, even if not as sharp as the Sigma.

I do have one more question, if you'll bear with me: does ISO performance really depend solely on the total area and Q.E. of the sensor? If there really nothing (or only a small amount) to be gained due to better noise reduction algorithms? I know that Canon advertises the DIGIC model in their bodies, so I had thought that going from the DIGIC 3 to the 5+ might be of some help at low light -- or is that all just marketing hoopla?


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## sagittariansrock (May 13, 2014)

tevscale said:


> Thanks to all who took the time to respond! The detailed information is extremely helpful. It looks like the 6D with 24-105 kit lens (to replace the field of view range of my 18-55 EF-S), and upgrading my 50mm to an f/1.4 would meet essentially all my needs. Of course that opens the door to the Sigma vs. Canon debate regarding the 50mm f/1.4, but I'm thinking that the Canon would be good enough, even if not as sharp as the Sigma.
> 
> I do have one more question, if you'll bear with me: does ISO performance really depend solely on the total area and Q.E. of the sensor? If there really nothing (or only a small amount) to be gained due to better noise reduction algorithms? I know that Canon advertises the DIGIC model in their bodies, so I had thought that going from the DIGIC 3 to the 5+ might be of some help at low light -- or is that all just marketing hoopla?




I think the newer crop sensors are much better, for example the 70D>>7D.
However, they can't come anywhere near the FF sensors.


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## bholliman (May 13, 2014)

Mt Spokane Photography said:


> Try borrowing or renting a 6D and a 70D (Pass on the 7D, its not very good in low light). Try them both a ISO 25600.
> 
> The bottom line is that you pay a lot of $$ for a incremental improvement in the APS-C line, which is why jumping to a 6D may be attractive for low light use, and almost everything else.



+1 As a 6D owner and father of an active 2-year-old, I strongly recommend it. I purchased a 6D last year and almost never used my 7D after that, and eventually sold it. The 6D produces very nice images at ISO 3200 and even 6400. I prefer flash photography when it's an option, but there are places it's not allowed or would be disruptive. For example if you want to get some candid shots of kids interacting, you really don't want to distract them with flash.

Regarding the 6D's AF and frame rate for moving kids or other things moving, I find it to be good enough. We recently attended a birthday party with lots of under 5 kids and I was pleased with the number of good, in-focus shots I came home with. I'm sure a 5D3 or 1Dx would have captured more good shots (higher FPS, better AF), but personally I can't justify the difference in price. I feel like my current equipment exceeds my skill as a photographer anyway.


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## Maximilian (May 13, 2014)

tevscale said:


> I do have one more question, if you'll bear with me: does ISO performance really depend solely on the total area and Q.E. of the sensor? If there really nothing (or only a small amount) to be gained due to better noise reduction algorithms? I know that Canon advertises the DIGIC model in their bodies, so I had thought that going from the DIGIC 3 to the 5+ might be of some help at low light -- or is that all just marketing hoopla?


Hi tevscale!
And welcome to this forum.

As you have stated in your original post, you prefer to use RAW files instead of JPEGs out of the camera. 
(This I always would recommend with the only exception of storage space needed)
The DIGIC processors are mostly responsible for higher speeds of in-camera processing. So they are therefore increasing the frames per second and maybe calculating more complex algorithms in the same time.
If you use RAW the processing and algorithms depend on your RAW converter SW on your pc.

Back to your original question:
Depending on how much money you are willing to spend I wouldn’t directly point to FF. (although I also have and love to use FF). Of course it is very often delivering a better IQ but maybe APS-C is still enough for you. And if it is so, you wouldn’t have to spend so much money on lenses a FF camera is demanding for.
You could lend a 70D. And then you can try out if the IQ fits to your demands. But then I would consider the new STM kit lens, because its IQ should be much better than that of your 18-55.
Let us know about your choice.


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## hgraf (May 13, 2014)

tevscale said:


> Let me start by explaining my situation: I'm relatively new to photography (have been using a DSLR for about 2 years) and primarily shoot my kids at their various activities and outdoor/nature scenes (with a preference for individual plants or animals rather than landscapes).
> 
> My current equipment consists of a Rebel XS with 18-55 EF-S kit lens, 50mm 1/8, 80-200 2.8 L, and 430 EX II flash. For well over 90% of what I want to do, this is just fine, and has provided some shots that I'll treasure for the rest of my life (most of the shots I miss are due to me, not the gear). But remaining few % is irritating! Most of my problems are in low light (indoor event for the kids where flash isn't allowed or I'm too far away to use it) where I could benefit from better high ISO performance than the Rebel can offer. The other issue is catching the "key moment" when action is occurring, where the Rebel's frame rate isn't up to the task (I shoot RAW since I don't think the JPEGs from the Rebel are particularly good, and that reduces the frame rate to about 1-2Hz).
> 
> ...



If you want ISO3200 to look like ISO800 on your Rebel, there is no APS-C option out there. The 7D and 70D are "better" then the XS in ISO performance, but not 2 stops, I'd say 1 stop is pushing it.

I still shoot with my XS, so I've very familiar with what it can do.

To battle low light then you have 2 options: get a full frame camera or get a faster lens. The Sigma 18-35 1.8 will do the latter, so that's an option. So are primes.

As for frame rate, first off try a faster SD card, that might get you a little more speed with the XS. But if you really want frame rate you'll have to go for either the 7D, 70D or 5DIII.

As for going full frame and replacing your 18-55, you don't need to go L, or even IS. There are many cheaper full frame regular zoom options that don't break the bank, especially on the used market. Yes, they won't have the amazing sharpness of L glass, but if you're up at 3200ISO it's not going to make that much difference anyways. There is always the 24-105L which is often sold grey box for really good prices.


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## hgraf (May 13, 2014)

tevscale said:


> I do have one more question, if you'll bear with me: does ISO performance really depend solely on the total area and Q.E. of the sensor? If there really nothing (or only a small amount) to be gained due to better noise reduction algorithms? I know that Canon advertises the DIGIC model in their bodies, so I had thought that going from the DIGIC 3 to the 5+ might be of some help at low light -- or is that all just marketing hoopla?



If you are shooting RAW then what the DIGIC does with your image from the point of PP is pretty much moot. When you shoot RAW your RAW converter is doing all that work. Lightroom/Aperture will almost always be better at getting what you want since you have nearly infinite control. DIGIC bakes things into the JPG based on a very small range of selections.


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## wsmith96 (May 13, 2014)

I'm in agreement with those who are recommending the 6D camera. I do not have one myself, but given the types of photo's you will be taking (per your description), I think that the 6D would solve your low light concerns. It's tough to think of it this way, but the 6D is the "rebel" of the FF product line, meaning that the learning curve between the two families may not be as great as would be if you were to upgrade to a 5D. This may, or may not be of concern to you. But, you can't have it all with a "budget" FF - you will sacrifice frame rate. 

I myself am waiting on this elusive unicorn called 7DMkII to see what it can do. Most of my photography is family event oriented so having a slight bit of noise in my low light images is fine with me. Actually, I find that my rebel does pretty well for a crop camera up to ISO 1600. If I'm printing the image out though, I won't go above 800. If I can get ISO 800 quality from a 1600 setting on a 7DMkII, I'd be happy.

Here's a link that you can use to compare the noise qualities between a few crop cameras and a single full frame. I wish there was a tool on this website to do a direct noise compare between reviewed cameras, but this should paint a picture for you.

http://www.the-digital-picture.com/Comparisons/Canon-EOS-Rebel-T2i-550D-Digital-SLR-Camera.aspx


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## Mt Spokane Photography (May 13, 2014)

tevscale said:


> I do have one more question, if you'll bear with me: does ISO performance really depend solely on the total area and Q.E. of the sensor? If there really nothing (or only a small amount) to be gained due to better noise reduction algorithms?


 
The Digic processor converts raw data to jpeg, and does a better looking job in newer cameras when compared to older ones. When using raw, digic plays no part in high ISO performance, its based on your software. Any improvements in algorithms (and there have been a lot in the past 5 years) will be applied to images from your XS or any other raw image. Thus, I can process raw images from a 20D or 40d and get a essential upgrade in high ISO performance. Jpeg on the older cameras is limited by the old processing firmware in the camera body, but raw is not, so your raw images can be upgraded. I used to think that raw images at ISO 1600 on my 40D were awful, but I reprocess them with newer software and they now look great. You can not do that with jpegs, since the raw to jpeg conversion is burned in.

One thing that newer camera bodies do have is slightly better noise reduction circuitry on the sensor chip. That's why you see a slightly better high ISO performance.

Getting lenses that add 1/2 stop or 1 stop is the way to go. Instead of the 24-105mmL, get a 24070mm f/2.8. You are limiting performance gained with FF by getting a f/4 lens. You can use the 24-70 at full aperture.

The other option is to get fast primes, f/2 to f/1.2. I'd not bother to upgrade your 50mm f/1.8 to f/1.4, you will not like images taken at f/1.4, there is a noticible decrease in performance. Spend your $$ on a better zoom, or high quality fast prime.


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## dgatwood (May 14, 2014)

ajfotofilmagem said:


> Canon 6D will show improvement in high ISO you want, but do not get too many pictures per second, perfectly focused. The focus points are not very sensitive and efficient, with the exception of the central point.



Compared with an XS? The focusing system in the 6D is still a step up, I think, with 11 points instead of 7, and pretty much all other attributes being similar, AFAIK.

I moved from an XTi (same sensor as the XS, but with the older, 9-point, non-cross focusing system, no live view, but otherwise very similar to the XS). The 6D (with a 24-105L) is night and day better in every way. Focusing is more consistent, and the high ISO makes it possible to take shots that were just unimaginable with the XTi. I've often quipped that the 6D does a better job taking photographs in an auditorium with the house lights off (using stage bleed) than the XTi did with the lights on....

If you really want a low-light upgrade, wait until you can get either a 6D or a 5Dmk3. Either one will be a truly jaw dropping experience the first time you take it into low light.


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## dgatwood (May 14, 2014)

Mt Spokane Photography said:


> One thing that newer camera bodies do have is slightly better noise reduction circuitry on the sensor chip. That's why you see a slightly better high ISO performance.



Not noise reduction circuitry, so much as less noisy circuitry, AFAIK. You commonly reduce noise by:

[list type=decimal]
[*]Cooling the image sensor to reduce thermal noise (mainly used when doing astrophotography)
[*]Moving amplifier circuits closer to the actual detectors—the photo sites, in this case—so you're amplifying less induced noise
[*]Using cleaner amplifier circuits that add less noise to the signal
[*]Improving the ADC circuitry that converts the analog voltage into a series of bits—adding precision, lowering the noise floor, etc.
[*]Increasing the consistency of amplifier circuits and ADCs to avoid banding when multiple ADCs are needed to capture a single frame (for speed reasons)
[*]Increasing the effective size of the photo sites on the image sensor by increasing the sensor's dimensions, moving chip features that partially occlude the sensor, etc.
[/list]

There are probably many other techniques that I'm forgetting.


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## dgatwood (May 14, 2014)

jrista said:


> Fundamentally, ISO/noise performance is a factor of two things: Real sensitivity (quantum efficiency) and *total *sensor area. Assuming you frame your subject the same, the only way to really reduce noise is to use a larger sensor. Pixel size does not really play a role unless your only putting the same number of pixels on the subject (which means you are not necessarily framing the same). With the same number of pixels on subject, then pixel size matters, and larger pixels do better.



That's only true for shot noise. You're forgetting read noise and thermal noise, neither of which is necessarily tied to sensor size in any way. For more info, read:

http://www.clarkvision.com/articles/digital.sensor.performance.summary/#SNR


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## Zv (May 14, 2014)

I think maybe what OP is experiencing is shutter lag. I noticed this on the rebel T2i. I'd see something like a person making a funny expresion and by the time the camera took the picture the moment was gone. I got frustrated and bought a 7D for it's speed but 99% of my shots were in One Shot mode. The 7D has very little shutter lag and as long as you have a decent CF card you'll not be waiting for ages to take your next shot. 

I'm not saying buy a 7D but buying anything above the rebel line will show improvements in speed and useablity. With good timing a 6D should suffice. I find the 5D 2 to be just fine for most things. It hasn't let me down yet. I can only imagine the 6D to be even better, especially in low light. 

I think investing in a good USM lens will also help you. After that try using back button focus technique to speed things up and to be always ready! 

Good luck!


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## jrista (May 14, 2014)

dgatwood said:


> jrista said:
> 
> 
> > Fundamentally, ISO/noise performance is a factor of two things: Real sensitivity (quantum efficiency) and *total *sensor area. Assuming you frame your subject the same, the only way to really reduce noise is to use a larger sensor. Pixel size does not really play a role unless your only putting the same number of pixels on the subject (which means you are not necessarily framing the same). With the same number of pixels on subject, then pixel size matters, and larger pixels do better.
> ...



Well, partially true. Pixel area is died to read noise. Larger pixels, as much as they are capable of carrying a larger charge due to photon strikes, are ALSO prone to experiencing more noise from dark current. This is evident in the actual measurements of Canon sensors. Check out sensorgen.info...you'll notice a very high correlation between pixel size and read noise levels. 

There are indeed some other components of read noise, which are primarily caused by high frequency component oscillations, however overall, read noise is a TINY contribution of noise overall. At higher ISO settings, read noise is at its minimums (~3e-), where as photon shot noise is at it's maximums. For a very high ISO setting, say ISO 3200, where the saturation point may be around 1000e-, the photon shot noise is ~32e-. Even though there is some read noise, it's trounced by photon shot noise (by a factor of ten or more, usually).

So I stand by what I said before. At higher ISO settings, noise performance is by far a factor of pixel size, not of read noise. Realize, a read noise of 3e- is the same as the D800 has at ISO 100. It's extremely low, trivial. ISO/noise performance is a factor of pixel size and quantum efficiency, read noise is such a small factor that it doesn't matter.


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## jrista (May 14, 2014)

dgatwood said:


> Mt Spokane Photography said:
> 
> 
> > One thing that newer camera bodies do have is slightly better noise reduction circuitry on the sensor chip. That's why you see a slightly better high ISO performance.
> ...



There is noise reduction circuitry. It's called CDS, or correlated double sampling. There is usually a CDS unit per column, which samples dark current before an exposure is made, and that sampling is subtracted from the pixel charge as each row is read. 

Now, as far as I am aware, Canon's CDS technology hasn't really changed much in a long time. It may have been tweaked, but I don't suspect any of those tweaks would result in a significant improvement in their hardware noise reduction. 

As for the ADC units, the reason ADC units introduce noise is because they are high frequency. Canon uses eight channels in most of their modern cameras, and sixteen in their 1D X. At approximately 5200 to 5600 columns, that means each ADC unit with 8 channels has to process an average of 675 columns of pixels each, or an average total of around 2.5 million pixels each, in a fraction of a second. Canon has low ADC parallelism, and as a result of that low parallelism, each ADC unit must run at a high frequency, which means the frequency of the clock is closer to the frequency of noise in the circuit itself. Additionally, the clock and power supply for the ADC units is right next to them in the DIGIC processors.

Sony Exmor sensors use column-parallel ADC. They moved the ADC onto the sensor die, and hyperparallelized them. That means each ADC unit in an exmor is only responsible for handling a few thousand pixels, instead of a few million pixels, every fraction of a second. That allows a lower frequency to be used, so the frequency of the clock is lower than the frequency of noise in the circuit itself. (Sony also move the clock and power supply themselves off to a remote corner of the Exmor die, which reduces potential thermal sources and, at least according to Sony's paper on the Exmor design, reduces noise from high frequency components within the ADC units themselves.) 

So I wouldn't say that moving the ADC unit closer to the detectors really has anything to do with reducing noise. Increasing the parallelism of the ADC units, allowing each one to operate at a lower frequency, has a lot to do with reducing noise. Because the ADC units are on-die with Exmor, it also means that the signal is converted from analog to digital immediately...rather than after transit across a bus and through who knows how many additional electronics. In Exmor, pixels are read, amplified, converted to digital via the ADC, and digital CDS is applied. From that point on, the DIGITAL signal can be moved around anywhere, error-corrected transfer can be used, and the signal, since it is now bits rather than analog charge, can be kept pure and accurate.

Canon actually has their own patent for an on-sensor-die column-parallel ADC. Canon's is called a "dual scale" ADC, in that their hyperparallel ADC units can actually operate at two frequencies. When necessary, they can operate at a lower frequency, which again reduces the amount of noise introduced. I think Canon moving from an off-die, high frequency, low parallelism ADC system to an on-die, low frequency, high parallelism ADC system is the key to them achieving lower noise. I don't think that moving the ADC's closer to the pixels in and of itself really reduces noise much...maybe a little, as it avoids the need to move the signal across a bus to external units, but overall, I think the lower operating frequency is really what will reduce noise. 

Canon also has patents for some other interesting technology. Such as a read-time power disconnect, which decouples pixels being read from the power source, which, at least theoretically as I understand it, could potentially eliminate dark current entirely as a contributor of read noise. That would help shadow noise performance a lot when shooting in higher temperatures...such as outdoors, in the sunlight, for birds, wildlife, landscapes, etc. (I know that my 7D can get pretty hot when I'm out in the sun trying to photograph birds or wildlife...which can take a lot of time to get close, get the right angle, etc.)


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## dgatwood (May 15, 2014)

jrista said:


> There is noise reduction circuitry. It's called CDS, or correlated double sampling. There is usually a CDS unit per column, which samples dark current before an exposure is made, and that sampling is subtracted from the pixel charge as each row is read.



Ah. I assumed that was being done in software rather than hardware.




jrista said:


> Sony Exmor sensors use column-parallel ADC. They moved the ADC onto the sensor die, and hyperparallelized them. That means each ADC unit in an exmor is only responsible for handling a few thousand pixels, instead of a few million pixels, every fraction of a second. That allows a lower frequency to be used, so the frequency of the clock is lower than the frequency of noise in the circuit itself.



I knew they'd moved it onto the die. I didn't know about the parallelization. That's an interesting approach. I'd be curious whether the use of lots of ADCs causes banding problems like it does for the 5DmkIII.

That might improve sampling accuracy, but at first glance, I would think that you could achieve similar benefits with oversampling. Maybe not.




jrista said:


> (Sony also move the clock and power supply themselves off to a remote corner of the Exmor die, which reduces potential thermal sources and, at least according to Sony's paper on the Exmor design, reduces noise from high frequency components within the ADC units themselves.)



Hmm. I guess that makes sense. With my audio hat on, when I hear someone talk about moving an ADC clock away from the ADC, my mind screams "Aaaah! The jitter! It burns!", but I suppose that jitter doesn't affect this use case very much, because the value isn't changing....




jrista said:


> So I wouldn't say that moving the ADC unit closer to the detectors really has anything to do with reducing noise.



Well, the more important thing is for the first gain stage to be as close as possible to the detectors. Any noise bleeding into the signal at that point is going to be massively amplified, so you would want to have as little distance there as possible. I'd expect the distance from there to the ADC to matter, albeit not nearly as much.




jrista said:


> Increasing the parallelism of the ADC units, allowing each one to operate at a lower frequency, has a lot to do with reducing noise. Because the ADC units are on-die with Exmor, it also means that the signal is converted from analog to digital immediately...rather than after transit across a bus and through who knows how many additional electronics.



And I suspect you can probably use less signal amplification, because you don't have to send the analog signal a long distance across a bus.




jrista said:


> Canon also has patents for some other interesting technology. Such as a read-time power disconnect, which decouples pixels being read from the power source, which, at least theoretically as I understand it, could potentially eliminate dark current entirely as a contributor of read noise. That would help shadow noise performance a lot when shooting in higher temperatures...such as outdoors, in the sunlight, for birds, wildlife, landscapes, etc. (I know that my 7D can get pretty hot when I'm out in the sun trying to photograph birds or wildlife...which can take a lot of time to get close, get the right angle, etc.)



Are we talking about ringing on the power supply rails here, or something else?


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## jrista (May 15, 2014)

dgatwood said:


> jrista said:
> 
> 
> > There is noise reduction circuitry. It's called CDS, or correlated double sampling. There is usually a CDS unit per column, which samples dark current before an exposure is made, and that sampling is subtracted from the pixel charge as each row is read.
> ...



CDS? CDS has to be done in hardware, since it requires sampling the actual dark current moving through the circuit. The closer the sampling is to the time the dark current is subtracted, the more accurate. This means that for shorter exposures, analog CDS is very accurate. 

The first Exmor design, the ones used in still photography sensors, used only digital CDS. The later Exmor designs actually use a dual CDS design, one analog CDS stage and one digital CDS stage. The analog stage takes care of most of the dark current noise, and the digital CDS stage takes care of any residual. As far as I know, the dual-CDS Exmors are only used in video camera sensors at the moment, but I suspect that won't remain that way for long. I actually suspect that the A7s sensor uses a dual CDS approach.



dgatwood said:


> jrista said:
> 
> 
> > Sony Exmor sensors use column-parallel ADC. They moved the ADC onto the sensor die, and hyperparallelized them. That means each ADC unit in an exmor is only responsible for handling a few thousand pixels, instead of a few million pixels, every fraction of a second. That allows a lower frequency to be used, so the frequency of the clock is lower than the frequency of noise in the circuit itself.
> ...



From what I've read about Sony Exmor, since the ADCs are per-column, that allows the potential to tune each ADC to handle column response differential. The responses of each ADC can be normalized to eliminate vertical column banding.

In the case of both the 7D (to a fairly strong degree) and the 5D III (very slightly), there is noticable vertical banding that correlates with each set of readout channels. In the 7D, you can clearly tell that each vertical band is 8 pixels wide, which corresponds with the 8 readout channels. In the 5D III, the effect is very subtle, so I figure Canon must have figured out a way of tuning or otherwise correcting for the readout differential for each ADC channel.

Anyway, there is potential for vertical banding with parallel ADCs, but it can always be tuned out or otherwise corrected for. With lower frequency per-column ADCs it's easier to fine-tune each ADC.



dgatwood said:


> That might improve sampling accuracy, but at first glance, I would think that you could achieve similar benefits with oversampling. Maybe not.



It sounds like you understand audio signal processing. While I think some aspects of standard signal processing apply, there are a lot of differences with spatial signal processing. I don't know standard audio signal processing all that well, so I can't say how sampling techniques might apply, but my gut (based on what I do know about spatial signal processing) tells me that there really isn't going to be much in the way of multi- or over-sampling the signal. It generally comes out of the sensor "as is", with the exception of what CDS does. 

Now, I do know that Sony, Nikon and a few other manufacturers do some things differently than Canon. It's often called "processing", but in general it's simple things. For example, Canon uses a bias offset in their design to handle the sensor bias signal, where as Sony and Nikon clip the bias signal out entirely (cleaner deep shadow noise, but you lose a good chunk of deep shadow.) For normal photography, clipping seems to be better, however for astrophotography (an arena where Canon cameras are almost synonymous with "modded DSLR") a bias offset is a far better approach as it means with more advanced noise removal techniques, you can recover a hell of a lot more signal from DEEP within the read noise. (Since that signal is clipped in Sony and Nikon sensors, its just gone, discarded, not recoverable.)



dgatwood said:


> jrista said:
> 
> 
> > (Sony also move the clock and power supply themselves off to a remote corner of the Exmor die, which reduces potential thermal sources and, at least according to Sony's paper on the Exmor design, reduces noise from high frequency components within the ADC units themselves.)
> ...



I don't gather, from the patents and papers, that the Exmor design was easy to achieve. When you look at the sensor layout, you can see in the upper left corner there is a clock, PLL, and a couple other components. Then you have the pixel array, with the photodiode, per-pixel amplifier, and the row/column activate and read wiring. Below that along the bottom you have the CP-ADC units, which contains a ramp ADC, the CDS/Pixel register (CDS readout counts negative, pixel readout counts positive, CDS is effectively "automatic"), and then some more electronics to ship the signal off the die. There are a few other components as well, although it's been long enough that I don't remember all of them. 

Anyway, however Sony did it, they seem to think that moving the high frequency components off to an isolated area of the die reduced noise and jitter in the ADC units, which is part of the reason the Exmor readout is so clean. Plus, since each ADC is only responsible for reading out a few thousand pixels they can be clocked slower (whatever the image height is, basically, so in a 6000x4000 pixel sensor, each ADC unit is only responsible for 4000 pixels per read, vs. say Canon's which are responsible for 2.5 million pixels per read).



dgatwood said:


> jrista said:
> 
> 
> > So I wouldn't say that moving the ADC unit closer to the detectors really has anything to do with reducing noise.
> ...



The gain is applied by the amplifiers, not the ADC. Maybe you have the two mixed up? While I'll admit I haven't read patents for every possible image sensor design, in the case of CMOS sensors, every pixel always has an amplifier. They are built into the readout logic for each and every "pixel". Now, in some sensor designs use a "shared pixel" design where two or more photodiodes will share some readout logic. Usually, in shared pixel designs, there is one amplifier for every two pixels, connected diagonally. This allows for a larger (longer) amplifier, which I guess improves effectiveness or efficiency (this gets into a realm of CMOS transistor design that is a bit beyond my level of understanding...but I believe it falls into the same category as FinFET and Tri-gate technology...a long thin "fin" of a transistor with multiple source and drain connections allows for cleaner, lower noise, lower head electron transfer). 

Anyway, yes, all pixels do have an amplifier right in the pixel, although not all pixels have their own amplifier. Some amplifiers are shared among pixels, however sharing allows for more efficient use of die space, meaning larger amplifier transistors and larger photodiodes, so higher efficiency overall. 

One caveat, Canon cameras have two amplifiers. There is of course the per-pixel amplifiers. These kick in AT read time, so they amplify the signal in the pixel directly before anything else happens to it, so it's before any additional noise is added to the signal. However, to achieve the highest ISO settings (usually the top two or three), Canon also uses an off-die, downstream secondary amplifier. This secondary amp is also a source of noise in Canon sensors. I don't know why they do this, however I found a rather old article somewhere a couple of years ago that indicated that Canon somehow determined that the downstream amplifier was actually less noisy. I don't know enough about the specifics to be able to say one way or myself for sure...but I guess I'm willing to trust that Canon knows what they are doing. 



dgatwood said:


> jrista said:
> 
> 
> > Increasing the parallelism of the ADC units, allowing each one to operate at a lower frequency, has a lot to do with reducing noise. Because the ADC units are on-die with Exmor, it also means that the signal is converted from analog to digital immediately...rather than after transit across a bus and through who knows how many additional electronics.
> ...



I'm not sure in this case. I'm sure that sending the signal over the bus introduces noise, however for the most part, amplification occurs in the pixels before any transfer across a bus. The one exception would be the top two ISO settings in Canon cameras (not the expanded settings, the top two native ISO settings), which uses a downstream amp.

Regardless, I think digital readout is the way of the future. Digital signals can be transmitted with error correction, and at very high speeds, without having to be concerned about analog noise interfering with the signal. With transistor sizes on sensors dropping to around 65nm now, that leaves a TON of room on the die for complex logic. I really hope Canon moves to a fully on-die system soon. I know they already tested the some of their patents, like their dual-scale CP-ADC and some other enhancements on the 120mp APS-H sensor, where they were able to achieve 9.5fps "low noise" readouts. God only knows when they might actually employ the technology in the actual sensors that go into actual consumer products, though.



dgatwood said:


> jrista said:
> 
> 
> > Canon also has patents for some other interesting technology. Such as a read-time power disconnect, which decouples pixels being read from the power source, which, at least theoretically as I understand it, could potentially eliminate dark current entirely as a contributor of read noise. That would help shadow noise performance a lot when shooting in higher temperatures...such as outdoors, in the sunlight, for birds, wildlife, landscapes, etc. (I know that my 7D can get pretty hot when I'm out in the sun trying to photograph birds or wildlife...which can take a lot of time to get close, get the right angle, etc.)
> ...



No, it was a fairly specific patent about a specific transistor setup around the pixels and some other logic in the sensor to disconnect the _active _power supply during readout (I think there was still some power from capacitors...can't remember). I'll see if I can find the patent again. It's interesting, but it was long ago enough now that I honestly don't remember the specifics. 

At one point in time, I'd found a gold mine of patents for Canon. Stuff going back to the early 2000's. I probably still have the bookmark in my old Opera 12 bookmarks file. I'll see if I can dig it up, and hopefully the site is still around. Canon has a lot of cool patents, but they don't seem to employ them. At least, not in their stills cameras (I think they have used some of these patents in their video sensors....but that's nothing unusual, it seems everyone in the CMOS sensor game these days implements all the coolest stuff in video sensors. ).


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## dgatwood (May 15, 2014)

jrista said:


> dgatwood said:
> 
> 
> > Well, the more important thing is for the first gain stage to be as close as possible to the detectors. Any noise bleeding into the signal at that point is going to be massively amplified, so you would want to have as little distance there as possible. I'd expect the distance from there [the pixel preamp] to the ADC to matter, albeit not nearly as much.
> ...



Reread my last sentence with the bracketed clarification.  I was conceding your point that the ADC distance isn't the most critical part. And if the first gain stage is, in fact, on-die, then the distance to the second gain stage is less critical, though still important if you need those top ISO settings, and the distance from the second gain stage to the ADC is even less important.

That said, when you kick in that secondary gain stage, at least in the 6D, that's when noise changes from consistent to banded and ugly, which suggests to me that either the distance between the gain stages is a significant problem or the secondary gain stage is crap. But I could be wrong.




jrista said:


> One caveat, Canon cameras have two amplifiers. There is of course the per-pixel amplifiers. These kick in AT read time, so they amplify the signal in the pixel directly before anything else happens to it, so it's before any additional noise is added to the signal. However, to achieve the highest ISO settings (usually the top two or three), Canon also uses an off-die, downstream secondary amplifier. This secondary amp is also a source of noise in Canon sensors.



Yeah, I remember reading about that a while back. My thought was that if they moved the ADCs on-die, the secondary amplifier stage would obviously move along with it, and I'd expect the gain for those top ISO settings to be a lot cleaner, because they wouldn't be amplifying all the induced noise that tends to bleed in whenever you run analog signal lines a significant distance.




jrista said:


> I don't know why they do this, however I found a rather old article somewhere a couple of years ago that indicated that Canon somehow determined that the downstream amplifier was actually less noisy.



Than using a single, high-gain amplifier stage? Quite probably. I seem to recall that it's usually easier (or at least cheaper) to get clean gain with a couple of low-gain stages than with a single high-gain stage.

I still would expect they'd be better off dropping that second gain stage, moving to an ADC with greater bit depth (so that those weak signals don't get eaten by the digital noise floor), and then emulating that last gain stage by bit shifting or multiplication. But that's just a gut feeling. Maybe there's some subtle reason that this doesn't work... like running headlong into the minimum switching voltage of transistors in the ADC or something. But then again, if that were the case, I'd expect an amplifier circuit to have the same problems, so.... *shrugs*





jrista said:


> dgatwood said:
> 
> 
> > jrista said:
> ...



Well, I know alkaline batteries are quite electrically noisy, and I can only assume Lithium ion batteries are probably just as bad. So given the power source in question, it does make some sense. Then again, if it is an advantage during readout, would it not also be an advantage while it is collecting light? Or is that process entirely passive?

And speaking of dark current, when looking through various photos I've taken over the years, I get the distinct impression that the first photo I take at any given location has more noise than subsequent pictures shot in the same location under the same conditions. Is this my imagination, or is the dark noise compensation being too aggressive and/or failing to clear out minutes of noise accumulation before computing a reference black frame?


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## greger (May 18, 2014)

I think you will love what the 70D will give you that your Rebel cannot. When I upgraded to the 7D from a 40D my17-85 kit lens gained new life. The movies that you'll be able to take will make up for any lack of lowlight performance you may experience. It will serve you well until you can afford to buy Full Frame and by then new models will be out with even better performance than the 6D and 5D lll have now. Good Luck in your decision.


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## tevscale (May 22, 2014)

Thanks again for all the advice. I've just ordered a 6D + 24-105 kit; once it arrives and I get some time to get used to it I'll post again.


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## wsmith96 (May 23, 2014)

tevscale said:


> Thanks again for all the advice. I've just ordered a 6D + 24-105 kit; once it arrives and I get some time to get used to it I'll post again.



Congrats on the purchase!


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