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06-21-2016, 02:09 PM   #1
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The superiority of FF over APS-c re: Depth of Field

I keep hearing how superior FF is over APS-c regarding the issue of depth of field, yet no one has ever really shown me an example of this superiority in a photo... So I ran the numbers through Cambridgeincolour's Depth of field calculator to see exactly what kind of "superiority" we are talking about.


A 35mm lens on an APS-c camera with a 1.5 crop factor at f1.4 and focused at 2 feet gets you from 1.97ft to 2.03ft in focus. That's 0.06 feet.


Focused at 10 feet you get from 9.32ft to 10.78ft in focus. That's 1.46 ft.



A 50mm lens on a FF camera at f1.4 focused at 2 feet gets you 1.98ft - 2.02ft in focus. That's 0.04ft.


Focused at 10 feet you get 9.49ft - 10.57ft. That's 1.08 feet.




So how about 200mm/300mm fashion depth of field, right?


200mm lens at 2.8 focused at 10 feet gives you 9.96-10.04 feet in focus which is 0.09 feet on an APS-c 1.5x crop.


300mm lens at 2.8 focused at 10 feet gives you 9.97-10.03 feet in focus which is 0.06 feet on a FF sensor.




So clearly FF is about 30-40% better at shallow depth of field shots, on paper. I have been a professional photographer for over 30 years, I'd be hard pressed to take 2 photographs that could actually show anyone these differences.


There are many reasons to buy a FF camera, depth of field superiority really just isn't one of them in my opinion and I think the math and practical application back me up. If you can't see the difference, who cares?

06-21-2016, 02:17 PM - 1 Like   #2
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QuoteOriginally posted by Qwntm Quote
I keep hearing how superior FF is over APS-c regarding the issue of depth of field, yet no one has ever really shown me an example of this superiority in a photo... So I ran the numbers through Cambridgeincolour's Depth of field calculator to see exactly what kind of "superiority" we are talking about.


A 35mm lens on an APS-c camera with a 1.5 crop factor at f1.4 and focused at 2 feet gets you from 1.97ft to 2.03ft in focus. That's 0.06 feet.


Focused at 10 feet you get from 9.32ft to 10.78ft in focus. That's 1.46 ft.



A 50mm lens on a FF camera at f1.4 focused at 2 feet gets you 1.98ft - 2.02ft in focus. That's 0.04ft.


Focused at 10 feet you get 9.49ft - 10.57ft. That's 1.08 feet.




So how about 200mm/300mm fashion depth of field, right?


200mm lens at 2.8 focused at 10 feet gives you 9.96-10.04 feet in focus which is 0.09 feet on an APS-c 1.5x crop.


300mm lens at 2.8 focused at 10 feet gives you 9.97-10.03 feet in focus which is 0.06 feet on a FF sensor.




So clearly FF is about 30-40% better at shallow depth of field shots, on paper. I have been a professional photographer for over 30 years, I'd be hard pressed to take 2 photographs that could actually show anyone these differences.


There are many reasons to buy a FF camera, depth of field superiority really just isn't one of them in my opinion and I think the math and practical application back me up. If you can't see the difference, who cares?
Oh some folks have fudged some pretty convincing images.

But my APS_c images from this morning....








as posted here.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/132843-boke...ml#post3686194

This is definitely a place where you can challenge yourself, by looking at the images and seeing if you can pick out the FF images. According to the constant roar of Full Frame nonsense, it should be a snap.
06-21-2016, 02:34 PM   #3
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The amount of blur is different from the depth of field. The blur depends on diameter of the entrance pupils, placement of subject relative to hyper-focal distance. With two different lens focal length, same depth of field can be achieved even if they have very different diameter of the entrance pupil. Most people confuse both. If I use a 200mm f2 wide open, there is no way you can achieve the same background blur with a 50mm lens because you would need a 50mm f0.25 lens which does not exist. And if you use a 500mm f4, there is no way you can achieve the same completely smooth background with a 85 f1.4 lens. Therefore there is a gap between formats that can only be close via stitching, and when stitching can't be done, it is wrong to say that two different format can produce the same result. That's physically not possible. Interesting to see people defying the laws of physics for emotional reasons.

---------- Post added 21-06-16 at 23:41 ----------

QuoteOriginally posted by Qwntm Quote
So clearly FF is about 30-40% better at shallow depth of field shots, on paper.
Yes, thanks. You do the calculations on paper. Thanks for that. It's always good to nail it down from some references such as Cambridge in color.

QuoteOriginally posted by Qwntm Quote
If you can't see the difference, who cares?
I can see the difference (beyond paper), I posted a link where people can see how photos are taken with a 5DIII and a 200mm f2.
06-21-2016, 02:59 PM   #4
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APS-C will never be as good as FF no matter how many pics you post. But of course, you can get great pics with both! K-1 compared to K-3II gives me 3-4 stops more ISO to play with..all i care about

06-21-2016, 03:12 PM   #5
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QuoteOriginally posted by kenspo Quote
APS-C will never be as good as FF no matter how many pics you post. But of course, you can get great pics with both! K-1 compared to K-3II gives me 3-4 stops more ISO to play with..all i care about


"Never be as good" and "more than you need or can use" are two separate concepts.


I hear a lot of people saying "never be as good" and very few admitting FF is "more than they need or can ever use"
06-21-2016, 03:15 PM - 1 Like   #6
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In that case, i speak for my self. I often work at the limits of a camera. From APS-C to FF makes my day easier.
06-21-2016, 03:18 PM   #7
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QuoteOriginally posted by Qwntm Quote
"Never be as good" and "more than you need or can use" are two separate concepts.


I hear a lot of people saying "never be as good" and very few admitting FF is "more than they need or can ever use"
It's handy to have both.
06-21-2016, 03:19 PM - 1 Like   #8
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Pointless thread.
We [including the OP] have all been though this 1 million times already.

06-21-2016, 03:19 PM   #9
osv
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QuoteOriginally posted by Qwntm Quote
"very few admitting FF is "more than they need or can ever use"
that's not true, there have been multiple threads on this forum that had a bunch of people claiming that they didn't need ff and that they weren't going to get a ff camera.

most recently, for example: https://www.pentaxforums.com/forums/190-pentax-k-1/317788-k1-not-k1-question-2.html
06-21-2016, 03:20 PM   #10
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QuoteOriginally posted by biz-engineer Quote
The amount of blur is different from the depth of field. The blur depends on diameter of the entrance pupils, placement of subject relative to hyper-focal distance. With two different lens focal length, same depth of field can be achieved even if they have very different diameter of the entrance pupil. Most people confuse both. If I use a 200mm f2 wide open, there is no way you can achieve the same background blur with a 50mm lens because you would need a 50mm f0.25 lens which does not exist. And if you use a 500mm f4, there is no way you can achieve the same completely smooth background with a 85 f1.4 lens. Therefore there is a gap between formats that can only be close via stitching, and when stitching can't be done, it is wrong to say that two different format can produce the same result. That's physically not possible. Interesting to see people defying the laws of physics for emotional reasons.

---------- Post added 21-06-16 at 23:41 ----------


Yes, thanks. You do the calculations on paper. Thanks for that. It's always good to nail it down from some references such as Cambridge in color.


I can see the difference (beyond paper), I posted a link where people can see how photos are taken with a 5DIII and a 200mm f2.

150mm at F2.8 on APS-c focused at 10 feet gives you 9.92ft - 10.08ft in focus. That's 0.15 feet.
200mm at F2.0 on FF focused at 10 feet gives you 9.95ft - 10.05ft in focus. That's 0.09 feet.


And you think you would be able to demonstrate this difference in a photograph so anyone could see it? Really?


I still have no clue what you're talking about regarding stitching, sorry.
06-21-2016, 03:23 PM - 1 Like   #11
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I don't think anyone ever said FF offers "better" depth of field.

What is better, however, is the strength of background blur. @biz_engineer points it out, but I'll go one step further. Blur also depends on the distance from the subject to the lens; in many ways, you can say it is the ratio

focus distance / subject to background distance

that matters most. The closer you focus, the stronger the background blur. Longer focal lengths exaggerate this effect. People generally try to fill the frame with their subject. Let's use the FA77 as an example. Let's suppose that you can stand 5 ft away from the subject with the full-frame camera. On APS-C, you need to back up to 7 ft or so. Thus, the blur will be less because the focus distance has decreased. The aperture gets in there too, but you need to crank open the aperture far more than you might like to see significant difference--try it! One stop or so doesn't make a big difference because you can't increase the subject to background distance.
06-21-2016, 03:26 PM   #12
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QuoteOriginally posted by osv Quote
that's not true, there have been multiple threads on this forum that had a bunch of people claiming that they didn't need ff and that they weren't going to get a ff camera.

most recently, for example: https://www.pentaxforums.com/forums/190-pentax-k-1/317788-k1-not-k1-question-2.html


Just to be clear: I absolutely have NO PROBLEM with someone saying "I don't need full frame at all but I am going to get one because I want one and it's cool."


I don't need it at all for anything I do, but I want a K1. But I am also not delusional about what it can do for me and that's why I have not bought one, yet.


The price will come down eventually and it will get harder and harder to resist...

---------- Post added 06-21-16 at 04:29 PM ----------

QuoteOriginally posted by MadMathMind Quote
I don't think anyone ever said FF offers "better" depth of field.

What is better, however, is the strength of background blur. @biz_engineer points it out, but I'll go one step further. Blur also depends on the distance from the subject to the lens; in many ways, you can say it is the ratio

focus distance / subject to background distance

that matters most. The closer you focus, the stronger the background blur. Longer focal lengths exaggerate this effect. People generally try to fill the frame with their subject. Let's use the FA77 as an example. Let's suppose that you can stand 5 ft away from the subject with the full-frame camera. On APS-C, you need to back up to 7 ft or so. Thus, the blur will be less because the focus distance has decreased. The aperture gets in there too, but you need to crank open the aperture far more than you might like to see significant difference--try it! One stop or so doesn't make a big difference because you can't increase the subject to background distance.


I agree with everything you say, (except why not use a 105 on the FF, or a 50mm on the APS-c instead of backing and cranking...) it's just that in practice it's not as big a deal as some are trying to propose and definitely isn't going to instantly transform anyone who uses FF into Damien Lovegrove or any of the other photogs mentioned here.

Last edited by Qwntm; 06-21-2016 at 03:31 PM.
06-21-2016, 03:31 PM   #13
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QuoteOriginally posted by normhead Quote
Oh some folks have fudged some pretty convincing images.

But my APS_c images from this morning....








as posted here.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/132843-boke...ml#post3686194

This is definitely a place where you can challenge yourself, by looking at the images and seeing if you can pick out the FF images. According to the constant roar of Full Frame nonsense, it should be a snap.
Nice pics Norm. No way I can tell.
06-21-2016, 03:33 PM   #14
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QuoteOriginally posted by normhead Quote
Oh some folks have fudged some pretty convincing images.

But my APS_c images from this morning....








as posted here.
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/132843-boke...ml#post3686194

This is definitely a place where you can challenge yourself, by looking at the images and seeing if you can pick out the FF images. According to the constant roar of Full Frame nonsense, it should be a snap.

LOL. Nice shots regardless of the sensor size.
06-21-2016, 03:39 PM   #15
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QuoteOriginally posted by Tjompen1968 Quote
What's up with the crusade against the new FF? I am really confused here... It is the best DSLR ever made by Pentax. In ALL regards. The K-5 was awsome, then the K-3 that was alot of fun but the K-1, the K-1 is like superglue. It will give you technically better images than any Pentax DSLR before it. And it is soooo much easier to use.

Why don't you get one already? Stop being so bitter...
I don't really get it either. The K-1's not exactly expensive in any case.
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