# Most OOF Blur Lens



## K-amps (Oct 11, 2015)

For a given frame; 

which Canon lens would give most Out of focus blur? Would 200/F2 be more than 85/1.2? Would 600/4 be more than 200/2?

Is there a calculator to calculate this? DoF master can do the DoF, but has no place to enter frame dimensions.


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## rs (Oct 11, 2015)

In simple terms, the larger the entrance pupil, the shallower the DoF. Which means the 600/4 wins at 200mm, but the legendary 1200/5.6 beats it at 214mm. 

However, throw in distance from subject (taking into account framing and MFD), and you've got quite a complex calculation. 

This might help you: http://www.cambridgeincolour.com/tutorials/dof-calculator.htm


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## chromophore (Oct 11, 2015)

In simple terms, if we fix the subject magnification by adjusting the distance between the camera to the subject, then the size of a blur circle for a background object at infinity is going to be proportional to the entrance pupil diameter, regardless of the actual f-number or focal length.

For example, if you take a 50mm f/1.0 lens, and a 600mm f/4 lens, the entrance pupil diameters at infinity focus are going to be 50mm and 150mm, respectively. Taking these as approximations to the entrance pupil diameters when both lenses are focused so that the image magnification are both at 0.01 (i.e., in each case the subject is located at a distance such that one meter of subject height will correspond to an image height of 1 cm), then for objects behind the subject, infinitely far away, the blur circle from the 600/4 lens will be approximately three times the diameter of the circle produced by the 50/1.0.

However, this scenario is not applicable when background objects are not infinitely far away, which is almost always the case. The reason is that when objects not in the plane of focus are relatively near that plane of focus, the effect of f-number on blur circle diameter is stronger. Therefore, a lens like the 85/1.2L will exhibit a more rapid increase in the blur circle diameter as a function of background separation from the subject, but achieves less maximum blur than a slower but longer focal length lens like the 300/2.8. Again, the comparison we are speaking of is for a constant subject magnification.

This is why very fast aperture lenses of modest focal length have a distinctive look: although you could get more background blur with a telephoto lens, the combination of a relatively short focal length and a very fast aperture results in an image where you can see more of the background (field of view is larger), but the drop-off in sharpness is more dramatic. More background blur alone does not create this look.


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## chauncey (Oct 11, 2015)

OOF is but part of the equation...it's the quality of the OOF area, called bokeh, that sets these lenses apart.
http://www.thephoblographer.com/2013/10/27/five-lenses-bokeh-drool/#.VhoU92eBdr8
http://www.itsjustlight.com/photography-gear/best-canon-lenses-bokeh/


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## Tuke (Oct 11, 2015)

With this site: http://dofsimulator.net/en/ and "Lock frame" box crossed you get the easiest answer to your question!

50mm, f/1.0
- background blur: 1.138mm
- depth of field: 12.5cm

85mm, f/1.2
- background blur: 1.532mm
- depth of field: 15.7cm

200mm, f/2.0
- background blur: 2.162mm
- depth of field: 26.2cm

600mm, f/4.0
- background blur: 3.243mm
- depth of field: 52.5cm

1200mm,f/5.6
- background blur: 
- depth of field:

These are from full body shots. In macro distances the dof is yet another thing/problem.


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## jrista (Oct 11, 2015)

rs said:


> In simple terms, the larger the entrance pupil, the shallower the DoF. Which means the 600/4 wins at 200mm, but the legendary 1200/5.6 beats it at 214mm.
> 
> However, throw in distance from subject (taking into account framing and MFD), and you've got quite a complex calculation.
> 
> This might help you: http://www.cambridgeincolour.com/tutorials/dof-calculator.htm



The Canon 600/4 has a 150mm aperture, not a 200mm aperture. If it was 200mm, the lens would be f/3. That would be a monstrous lens.


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## scyrene (Oct 11, 2015)

I've considered this myself on and off. As you've all mentioned, it's quite complex as aperture (ratio and physical) interacts with both subject distance and background distance. Anecdotally, I'd say the 100L macro is a surprisingly good contender, when used closed to MFD with a distant background (the 180L must be better; the MP-E can be better, but has much more restricted use situations so it's hard to test side-by-side), the 85L is great, but the MFD is quite long so it's not so much better* (although I often found I needed to stop down as the background was *too* OOF sometimes) - but then the 500L+2x even stopped down to f/10 can produce lovely smooth backgrounds too, although something about that combination can make for busyness. I'd imagine the 200L or 400L, especially with extension tubes could be at the upper end, but all the (super) super teles are likely similar.

Sorry if I'm rambling 

*using with extension tubes helps of course.


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## Dylan777 (Oct 11, 2015)

Having to own 85L f1.2, 200f2 and 400f2.8 IS II, I like the blur on 200f2


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## rfdesigner (Oct 11, 2015)

jrista said:


> rs said:
> 
> 
> > In simple terms, the larger the entrance pupil, the shallower the DoF. Which means the 600/4 wins at 200mm, but the legendary 1200/5.6 beats it at 214mm.
> ...



For the record, my scope is a 1500mm/F5.. 1ft aperture. No Autofocus.. and it's a b***h to focus! DoF is simply absent.






Image taken during the drive development, hence the wires.


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## rs (Oct 11, 2015)

jrista said:


> rs said:
> 
> 
> > In simple terms, the larger the entrance pupil, the shallower the DoF. Which means the 600/4 wins at 200mm, but the legendary 1200/5.6 beats it at 214mm.
> ...



You'd think I could handle simple division, eh? 

Thanks for correcting me!


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## K-amps (Oct 12, 2015)

chromophore said:


> In simple terms, if we fix the subject magnification by adjusting the distance between the camera to the subject, then the size of a blur circle for a background object at infinity is going to be proportional to the entrance pupil diameter, regardless of the actual f-number or focal length.
> 
> For example, if you take a 50mm f/1.0 lens, and a 600mm f/4 lens, the entrance pupil diameters at infinity focus are going to be 50mm and 150mm, respectively. Taking these as approximations to the entrance pupil diameters when both lenses are focused so that the image magnification are both at 0.01 (i.e., in each case the subject is located at a distance such that one meter of subject height will correspond to an image height of 1 cm), then for objects behind the subject, infinitely far away, the blur circle from the 600/4 lens will be approximately three times the diameter of the circle produced by the 50/1.0.
> 
> ...



You start off explaining it very well. ..... but forget to answer my question  regardless, I did learn from it.

Can you explain this and I quote ''Therefore, a lens like the 85/1.2L will exhibit a more rapid increase in the blur circle diameter as a function of background separation from the subject, but achieves less maximum blur than a slower but longer focal length lens like the 300/2.8''


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## K-amps (Oct 12, 2015)

rs said:


> In simple terms, the larger the entrance pupil, the shallower the DoF. Which means the 600/4 wins at 200mm, but the legendary 1200/5.6 beats it at 214mm.
> 
> However, throw in distance from subject (taking into account framing and MFD), and you've got quite a complex calculation.
> 
> This might help you: http://www.cambridgeincolour.com/tutorials/dof-calculator.htm



Thank you, but my first stipulation was for a given frame, which DoF calculators ignore. You are right, fix the framing, and it gets quite complex. Interesting discussion.


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## K-amps (Oct 12, 2015)

chauncey said:


> OOF is but part of the equation...it's the quality of the OOF area, called bokeh, that sets these lenses apart.
> http://www.thephoblographer.com/2013/10/27/five-lenses-bokeh-drool/#.VhoU92eBdr8
> http://www.itsjustlight.com/photography-gear/best-canon-lenses-bokeh/



Thanks; I specifically asked for out of focus blur, not Bokeh. Discussing Bokeh is very subjective... Perhaps a question for a different thread.


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## K-amps (Oct 12, 2015)

Tuke said:


> With this site: http://dofsimulator.net/en/ and "Lock frame" box crossed you get the easiest answer to your question!
> 
> 50mm, f/1.0
> - background blur: 1.138mm
> ...



Sir, thank you for dumbing it down for me... You understood the question perfectly, and your esp is also sensational, in that you guessed the application as well... full body shots  .... Very helpful Answer. Takes a bow.


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## K-amps (Oct 12, 2015)

scyrene said:


> I've considered this myself on and off. As you've all mentioned, it's quite complex as aperture (ratio and physical) interacts with both subject distance and background distance. Anecdotally, I'd say the 100L macro is a surprisingly good contender, when used closed to MFD with a distant background (the 180L must be better; the MP-E can be better, but has much more restricted use situations so it's hard to test side-by-side), the 85L is great, but the MFD is quite long so it's not so much better* (although I often found I needed to stop down as the background was *too* OOF sometimes) - but then the 500L+2x even stopped down to f/10 can produce lovely smooth backgrounds too, although something about that combination can make for busyness. I'd imagine the 200L or 400L, especially with extension tubes could be at the upper end, but all the (super) super teles are likely similar.
> 
> Sorry if I'm rambling
> 
> *using with extension tubes helps of course.



We should meet over a cuppa ... and ramble some more on this topic


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## K-amps (Oct 12, 2015)

Dylan777 said:


> Having to own 85L f1.2, 200f2 and 400f2.8 IS II, I like the blur on 200f2



Thanks Dylan. I think I would like the 200F2 blur as well... just from some shots I have seen of the lens. But let me ask you, if you took a full body shot of your kid (or any subject filling a fixed part of the frame) , with all 3 lenses, (meaning you would have to physically move back for longer FL lenses); then for which of these three would you have the most background blur (not best Bokeh, but quantity of blur).

Heck if you can run a little test and post pics, I will pass on the favor to the next guy that has a similar question  

Deal?


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## scyrene (Oct 12, 2015)

K-amps said:


> scyrene said:
> 
> 
> > I've considered this myself on and off. As you've all mentioned, it's quite complex as aperture (ratio and physical) interacts with both subject distance and background distance. Anecdotally, I'd say the 100L macro is a surprisingly good contender, when used closed to MFD with a distant background (the 180L must be better; the MP-E can be better, but has much more restricted use situations so it's hard to test side-by-side), the 85L is great, but the MFD is quite long so it's not so much better* (although I often found I needed to stop down as the background was *too* OOF sometimes) - but then the 500L+2x even stopped down to f/10 can produce lovely smooth backgrounds too, although something about that combination can make for busyness. I'd imagine the 200L or 400L, especially with extension tubes could be at the upper end, but all the (super) super teles are likely similar.
> ...



Sounds good to me!


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## Dylan777 (Oct 12, 2015)

K-amps said:


> Dylan777 said:
> 
> 
> > Having to own 85L f1.2, 200f2 and 400f2.8 IS II, I like the blur on 200f2
> ...


I would say 200mm @ wide open due to the fl and f2 still my favorite. 85L f1.2 II is neck to neck. Big pros, weight, f1.2 and of course $$$.

Here are few shots from 200f2 @ wide open. I don't recall last time I shoot smaller than f2 with this lens.


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## scyrene (Oct 12, 2015)

Dylan777 said:


> K-amps said:
> 
> 
> > Dylan777 said:
> ...



I covet that lens more than any other. Such a pity it's so expensive - even more than the 300L II in street prices here


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## chromophore (Oct 12, 2015)

K-amps said:


> chromophore said:
> 
> 
> > In simple terms, if we fix the subject magnification by adjusting the distance between the camera to the subject, then the size of a blur circle for a background object at infinity is going to be proportional to the entrance pupil diameter, regardless of the actual f-number or focal length.
> ...



I did not forget to answer your question. The purpose of my response was to explain that your question does not furnish a sufficient set of conditions to uniquely answer it, because the amount of blur is not purely a function of the lens: it is a function of an interaction of lens and distance between subject and background.

Another thing I must point out is that DOF says almost nothing about the extent of blur: the DOF only indicates the range of distances at which objects appear acceptably sharp. Therefore, any DOF calculators or formulas that do not specifically calculate the blur circle diameter will be irrelevant to your question.

Years ago I wrote a program that would display a chart of the blur circle diameter as a function of image magnification, f-number, focal length, and distance between subject-in-focus and background. It's sitting on some backup drive somewhere so I would need to dig it out. The point is that a lens with a large entrance pupil may achieve more blur of background objects very far away, but the *rate* at which the blur circle diameter increases can be slower than another lens with a smaller entrance pupil diameter. This is precisely what happens if we compare an 85/1.2 against a 300/2.8. If you take headshots with both lenses at the same image magnification, and in both shots, you focus on the eyes, you will find that with the 85/1.2, the subject's nose will be much more blurry than with the 300/2.8. But a very distant background will be more blurry on the same shot at 300/2.8 than at 85/1.2. The *slope* of blur circle diameter as a function of subject-background separation is greater with the 85/1.2 but the *asymptotic behavior* of blur circle diameter is such that the 300/2.8 will achieve more blur.


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## chromophore (Oct 13, 2015)

So I dug up my program and here is a sample of the output for a comparison between an ideal 85mm f/1.2 lens versus an ideal 300mm f/2.8 lens. Note I say "ideal" here because in practice, the actual EF 85/1.2L and EF 300/2.8L IS II are not exactly 85mm or 300mm, nor are they exactly f/1.2 or f/2.8. But to a large extent, the model is a fairly good representation of what happens in practice.

What the plot shows is that for a subject magnification of 0.06 (meaning that an object in the plane of focus that is 100mm long will project an image onto the sensor that is 6mm long, which is roughly in the ballpark for portraiture), the red curve expresses the diameter of the blur circle for a 300/2.8 lens as a function of the distance between the subject and the background. In other words, when the subject is in focus and the camera-subject distance is adjusted so that the subject has an apparent magnification of 0.06, a point light source 1 meter behind the subject will be rendered as a blur disk with diameter about 1 mm on the sensor. For a point light source 100 meters behind the subject, the blur disk on the sensor will have a diameter of about 6.15 mm.

The blue curve corresponds to the 85/1.2 lens. To maintain the magnification of 0.06, you'd stand quite a bit closer to the subject than for a 300/2.8. But for an object 1 meter behind the subject, the 85/1.2 would have a blur circle diameter of about 1.6 mm, which is more blur than you would get with the 300/2.8 at this background distance. And then this situation is reversed for objects more than 6 meters behind the subject in focus!

So you can see that the extent of blur depends not just on the lens, but the spatial relationship between the subject and the background. And this plot shows exactly what I have been trying to explain: the 85/1.2 goes blurrier for nearby background objects, but not for faraway objects compared to the 300/2.8.


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## rfdesigner (Oct 13, 2015)

chromophore said:


> So I dug up my program and here is a sample of the output for a comparison between an ideal 85mm f/1.2 lens versus an ideal 300mm f/2.8 lens. Note I say "ideal" here because in practice, the actual EF 85/1.2L and EF 300/2.8L IS II are not exactly 85mm or 300mm, nor are they exactly f/1.2 or f/2.8. But to a large extent, the model is a fairly good representation of what happens in practice.
> 
> What the plot shows is that for a subject magnification of 0.06 (meaning that an object in the plane of focus that is 100mm long will project an image onto the sensor that is 6mm long, which is roughly in the ballpark for portraiture), the red curve expresses the diameter of the blur circle for a 300/2.8 lens as a function of the distance between the subject and the background. In other words, when the subject is in focus and the camera-subject distance is adjusted so that the subject has an apparent magnification of 0.06, a point light source 1 meter behind the subject will be rendered as a blur disk with diameter about 1 mm on the sensor. For a point light source 100 meters behind the subject, the blur disk on the sensor will have a diameter of about 6.15 mm.
> 
> ...



That is an impressive piece of work.

Can you publish the maths behind this please?.. I'm genuinely interested


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## K-amps (Oct 14, 2015)

chromophore said:


> if we compare an 85/1.2 against a 300/2.8. If you take headshots with both lenses at the same image magnification, and in both shots, you focus on the eyes, you will find that with the 85/1.2, the subject's nose will be much more blurry than with the 300/2.8. But a very distant background will be more blurry on the same shot at 300/2.8 than at 85/1.2. The *slope* of blur circle diameter as a function of subject-background separation is greater with the 85/1.2 but the *asymptotic behavior* of blur circle diameter is such that the 300/2.8 will achieve more blur.



This is great info, Gracias! Makes a lot of sense... it clears many things for me now.

The graph makes it even clearer. 

Can I use your information as reference to teach this to a group of budding photographers this concept?


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## TominNJ (Oct 14, 2015)

to get that creamy OOF background you need to work in the minimum focusing distance for the lens (get as close as you can), shoot wide open or the maximum aperture that will give you the DOF you need and position the camera so you have as much distance between the subject and background as possible.


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## chromophore (Oct 14, 2015)

K-amps said:


> chromophore said:
> 
> 
> > if we compare an 85/1.2 against a 300/2.8. If you take headshots with both lenses at the same image magnification, and in both shots, you focus on the eyes, you will find that with the 85/1.2, the subject's nose will be much more blurry than with the 300/2.8. But a very distant background will be more blurry on the same shot at 300/2.8 than at 85/1.2. The *slope* of blur circle diameter as a function of subject-background separation is greater with the 85/1.2 but the *asymptotic behavior* of blur circle diameter is such that the 300/2.8 will achieve more blur.
> ...



Yes of course; although this is a very technical topic and the relationships are rather complex. The general rule is that, *for a constant subject magnification*, in the distant background regime, entrance pupil diameter is the dominating factor. In the near background regime, the f-number is the dominating factor for the size of the blur circle. The subject-background separation distance at which the two switch over depends on the focal lengths being compared, the f-numbers being compared, and the subject magnification.

I would love to be able to show the way the plot changes with the selection of different parameters--it is a fully interactive plot--but this is not possible at this time.


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## K-amps (Oct 14, 2015)

chromophore said:


> K-amps said:
> 
> 
> > chromophore said:
> ...




Awesome thanks!

Can you post the graphical relationships between a few Canon L's for example:

50 1.2
85 1.2
100 2.8L
135 F2
180 3.5
200 2.8
200 F2
300 2.8
400 4
400 2.8
600 f4


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## Valvebounce (Oct 15, 2015)

Hi Folks. 
I dip into the photography technique threads every so often, this has been among the most interesting I have read, thank you to those that know and to the others that ask and draw that knowledge out! 

Chromophore, have you published this program of yours? Would you? How much? Does it work for zooms choose 1 focal length or only primes, only lenses that you have written it for? I love to put my lenses through software like this to have an idea how they behave, I have dof calculator and have spent way too long just putting numbers in to that! 

Cheers, Graham.


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## Tuke (Oct 15, 2015)

If you want graphs instead of numbers, why dont you use one of these?


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## K-amps (Oct 15, 2015)

Tuke said:


> If you want graphs instead of numbers, why dont you use one of these?



Excellent!


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## takesome1 (Oct 15, 2015)

K-amps said:


> which Canon lens would give most Out of focus blur?



I go with the 180mm L macro shot wide open at the minimum focal distance.


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## Steve Balcombe (Oct 15, 2015)

K-amps said:


> ... my first stipulation was for a given frame, which DoF calculators ignore. You are right, fix the framing, and it gets quite complex.



On the contrary, it makes it very simple (see below). It is also the most realistic and generally useful comparison - same sensor (we're comparing lenses, not cameras), and same framing (we're looking at alternative ways to take the same shot).



chromophore said:


> The general rule is that, *for a constant subject magnification*, in the distant background regime, entrance pupil diameter is the dominating factor. In the near background regime, the f-number is the dominating factor for the size of the blur circle.



I thought I'd better read all the responses before posting mine, and yours is the one which really gets this right. I'd like to rephrase it though. For a given sensor size and subject framing:

- distant background blur is proportional to entrance pupil size (i.e. focal length/f-number)

- depth of field is the same for the same f-number, regardless of focal length.

This means that if your aim is a head and shoulders portrait with enough depth of field to have the whole face and hair in focus, but with maximum background blur for subject separation, you should choose a long lens as that will give you more background blur at the required f-number. If your aim is to have one eye in focus, choose a shorter lens with a very large aperture.


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## K-amps (Oct 16, 2015)

Steve Balcombe said:


> - depth of field is the same for the same f-number, regardless of focal length.
> 
> This means that if your aim is a head and shoulders portrait with enough depth of field to have the whole face and hair in focus, but with maximum background blur for subject separation, you should choose a long lens as that will give you more background blur at the required f-number. If your aim is to have one eye in focus, choose a shorter lens with a very large aperture.



I thought DoF varies with FL, because framing would change with FL. So are we saying that a 50mm F1.2 will have same DoF as a 85mm F1.2 regardless of subject distance? 


I take it that background blur then depends both on subject distance and background distance then. Which one of these dominates?


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## Steve Balcombe (Oct 16, 2015)

K-amps said:


> I thought DoF varies with FL, because framing would change with FL. So are we saying that a 50mm F1.2 will have same DoF as a 85mm F1.2 regardless of subject distance?



I was careful to say that the DoF is constant _for the same framing_. We adjust shooting distance to make the framing the same - for example you will shoot a head-and-shoulders portrait from further away with an 85/1.2 than with a 50/1.2. That's how you get constant DoF. This is a very realistic comparison, because in terms of the subject it's the "same" shot. Not the same perspective of course, but that is an indirect consequence of using a different lens.



K-amps said:


> I take it that background blur then depends both on subject distance and background distance then. Which one of these dominates?



It does, but again I was careful to say _distant _background blur. Another way to look at it is _maximum _background blur, which is basically the same thing. However there is an underlying assumption that the subject is reasonably close - if your subject is a cityscape and the background is the mountains beyond, you won't get much background blur.

I'm not sure it's possible to answer the question in terms of which one "dominates", they both affect blur. 

I think there is a danger of losing the context here. The desire is for maximum background blur, and you are clearly not going to get this if the background is very close. Furthermore we are looking at lens options for the same shot of the same subject, so subject distance is dictated by that. If your choice of subject distance is limited, then your choice of focal length is also limited and the original question no longer applies.


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## meywd (Oct 16, 2015)

If you are shooting portraits - and not candids - then the brenizer method is a good way to overcome the OOF limitations of the lens, I know it can't be used for fast shots, but if you have the time its amazing.

this was made from 86 shots using the 70-200mm f/2.8 IS II @ 200mm f/2.8


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## chauncey (Oct 16, 2015)

Any amount of background blur is achievable with any lens set to it's most wide open setting 
via the use of PP...simply take the shot, then take another with whatever blur on whatever portion
of the image that you want the most blur, then merge them in PP. No brainer.


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## photonius (Oct 16, 2015)

Tuke said:


> If you want graphs instead of numbers, why dont you use one of these?



nice.
There is another site with lots of graphs, but not interactive:
http://www.zen20934.zen.co.uk/photography/dof/dof.htm


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## photonius (Oct 16, 2015)

Tuke said:


> With this site: http://dofsimulator.net/en/ and "Lock frame" box crossed you get the easiest answer to your question!
> 
> 50mm, f/1.0
> - background blur: 1.138mm
> ...



That's a new one I haven't seen before.
This one has been around for many years, but not well known:
http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html


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## PavelR (Oct 16, 2015)

photonius said:


> That's a new one I haven't seen before.
> This one has been around for many years, but not well known:
> http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html


Thank you very much for the link! It is finally the model that correspond to my experience that 400/5.6 produce bigger background blur than 200/2 = focal length is the most influencing variable (with decent distance subject ~ background about 10m+).


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## chromophore (Oct 16, 2015)

At present, I don't have the time to go through and generate plots for all the common EF primes, but I might be able to do that over the weekend. The problem is that there are a *LOT* of plots that would need to be generated, because for each lens, I would need to show a plot for a variety of subject magnifications and distance regimes. The curves *look* similar, but the axes and scales change. If I could publish it as a Wolfram Demonstration Project (the program is written in Mathematica), then it would be a simple matter for anyone to interact with it.

Anyway, the other reason I wanted to post here is because there are still some lingering misconceptions that I would like to clear up.

First, *depth of field is not the same as background blur*. Depth of field tells you what is in acceptable focus. If you have studied the plots I have provided thus far, you should understand by now that what the in-focus areas of the field does not say much, if anything, about what the out-of-focus areas will look like. Quantitatively, you can read off the DOF behind the subject in focus by drawing a horizontal line at the CoC (circle of confusion) diameter on the plot, and seeing where it intersects the curve. This intersection point corresponds to the distance behind the subject in focus for which objects will still appear "acceptably sharp."

The problem of course, is that by definition, objects within the DOF are "acceptably sharp," so it is difficult to ascertain with precision the actual distance at which a real-world lens is focused within the DOF. To a first-order approximation, for "non-distant" subjects, this distance is around the midpoint of the DOF (especially in the macro regime).

But back to blur circle diameter. For a given subject magnification, in the near regime, the DOF is *approximately* the same. It is not *exactly equivalent*. But in practice, any differences are not likely to be noticed for two reasons: (1) they are tiny; (2) the DOF is an abstraction that simplifies what is in fact a *continuous* phenomenon of increasing blur as a function of distance from the plane of sharpest focus, into a dichotomous outcome ("acceptably sharp" vs. "not acceptably sharp").

What we need to remember is that all our discussions in this thread pertain to the condition that all comparisons are to be made at a constant subject magnification; that is to say, regardless of focal length, the subject-camera distance is adjusted so that the subject in focus *appears the same size*. This may or may not be possible for all lenses, since some lenses cannot achieve the magnification factor that other lenses can (non-macro vs. macro being an obvious example).

So, if we want to make a fair comparison of what lenses give the greatest background blur for a given real-world scene, then we impose the following conditions: (1) We cannot change the subject, background, or relationship between them; (2) we are unwilling to do post-processing trickery; (3) we are allowed to choose the lens; (4) we are allowed to choose where we stand relative to the subject; (5) we are not concerned with differences in camera perspective as a consequence of subject-camera distance choice; (6) we do not model individual lens aberrations but model them as ideal lenses.

Then, under the above conditions, the appropriate comparison is done with the plots I have described. Again, what we see in the out-of-focus areas is a combination of factors. That an 85/1.2 can achieve more blur than a 300/2.8 in the near regime is not quantitatively explained any other way, because, as I must remind the reader of what I wrote at the beginning of this already very long response, the DOF tells us what is in focus. It doesn't tell us how rapidly something goes out of focus, at least not directly.


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## meywd (Oct 16, 2015)

chauncey said:


> Any amount of background blur is achievable with any lens set to it's most wide open setting
> via the use of PP...simply take the shot, then take another with whatever blur on whatever portion
> of the image that you want the most blur, then merge them in PP. No brainer.



huh?


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## chrysoberyl (Oct 16, 2015)

I like the blurred background achieved with my 100 L macro + 500D close-up lens.


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## chauncey (Oct 16, 2015)

> huh?


Aah...you're not a Photoshop user I take it.


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## chromophore (Oct 16, 2015)

chauncey said:


> > huh?
> 
> 
> Aah...you're not a Photoshop user I take it.



I use PS and even I was a bit confused by your original statement. I *think* what you mean is, take two photos: one photo has the subject in focus, and the other photo is focused in a way that deliberately blurs the background. Then merge the two together into a composite where the subject is sharp from the first image, and the background is blurred from the second. Is that correct?

If so, I should point out of course that this works only if (1) you can take the time to do it, both at the time of shooting and in post; (2) if you can move the subject for the second shot so that the defocused image of the subject is not larger than the area of the image containing the sharp subject; (3) the camera and background scene are relatively stationary; and most importantly (4) the subject and background relationship is such that the composition of the two in post is convincing. This last one is a sticking point for some shots because the transition from sharp to blurry is continuous for some scenes; e.g., a portrait of a person leaning against a wall, and the shot is taken roughly parallel to the face of the wall.


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## chauncey (Oct 16, 2015)

Your correct in that it would take more than one image, sometimes several of them.
Besides, someone that tends to rush their shots and fails to work the scene is a poor photographer.


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## Steve Balcombe (Oct 16, 2015)

chauncey said:


> Your correct in that it would take more than one image, sometimes several of them.
> Besides, someone that tends to rush their shots and fails to work the scene is a poor photographer.



You are trolling sir.


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## meywd (Oct 17, 2015)

chromophore said:


> chauncey said:
> 
> 
> > > huh?
> ...





chauncey said:


> Your correct in that it would take more than one image, sometimes several of them.
> Besides, someone that tends to rush their shots and fails to work the scene is a poor photographer.



if you meant doing a panorama that way, then yes that can work, however it may not produce a good result, you will need to take both at the same aperture, and even with that, with the example shot about, the person part itself consists of 10 shots or more, so having him stand still for a bit may be a better option.


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## jd7 (Oct 17, 2015)

Just wanted to say thanks to those who have contributed to this thread, and particularly Chromophore. I thought I understood about aperture and blur, but it turns out I didn't understand quite as much as I thought I did!


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## K-amps (Oct 17, 2015)

jd7 said:


> Just wanted to say thanks to those who have contributed to this thread, and particularly Chromophore. I thought I understood about aperture and blur, but it turns out I didn't understand quite as much as I thought I did!



+1 great stuff especially chromo


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## Pookie (Oct 17, 2015)

Owning the 200 f/2 and down in primes... I find it odd that the 135L is not mentioned at all here. In practical terms I doubt many would be able to discern images from 200 f/2, 135 f/2, 85 f/1.2 or 50 f/1.2. The 135 produces some of the finest quality bokeh of the entire bunch.


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## Dylan777 (Oct 17, 2015)

Pookie said:


> Owning the 200 f/2 and down in primes... I find it odd that the 135L is not mentioned at all here. In practical terms I doubt many would be able to discern images from 200 f/2, 135 f/2, 85 f/1.2 or 50 f/1.2. The 135 produces some of the finest quality bokeh of the entire bunch.



Sounds BS to me. 

Yes, it's good, but finest over 200f2 and 85f1.2?


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## scyrene (Oct 17, 2015)

Dylan777 said:


> Pookie said:
> 
> 
> > Owning the 200 f/2 and down in primes... I find it odd that the 135L is not mentioned at all here. In practical terms I doubt many would be able to discern images from 200 f/2, 135 f/2, 85 f/1.2 or 50 f/1.2. The 135 produces some of the finest quality bokeh of the entire bunch.
> ...



I've used neither the 200L nor the 135L, but from everything I've read and seen, the latter offers some of the best results *for its price*, but the 200L is just on another plane. As it should be for, what? 6x the price?


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## Dylan777 (Oct 17, 2015)

scyrene said:


> Dylan777 said:
> 
> 
> > Pookie said:
> ...



In Canon *L* line, how do we place justification on pricing?

300mm f4 IS Vs 300mm f2.8 IS II
400mm f4 Vs 400mm f2.8 IS II
List goes on...

It's up to individual to make that call. My take, prices have never been equal to quality in Canon L line. However, the looks and results in certain(difficult) situations are worth it.

Sorry OP for derailing your post.


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## scyrene (Oct 17, 2015)

Dylan777 said:


> scyrene said:
> 
> 
> > Dylan777 said:
> ...



I wasn't disagreeing with you, in case you misunderstood. Those examples are similar - the cheaper ones offer excellent image quality, but the expensive ones are something else (the differences in some metrics are greater than in others).

As for the rationale of actual pricing, it's not as simple as 'you get what you pay for' of course. Like, the 200L is still £4.5-5k here, but the 300L 2.8 can be had new for ~£3.5k - perhaps the street prices reflect demand, I dunno.


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