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FORUMS Photography Talk by Genre Macro Talk 
Thread started 11 Apr 2017 (Tuesday) 15:25
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Which Canon body for Macro?

 
Chris.R
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Jun 05, 2017 12:28 |  #46

Archibald wrote in post #18371445 (external link)
Conclusion: the crop format (for the stated premises) has a significant advantage.

I think you must have done something I wouldn't, in your maths :)
Better brains than mine have shown equivalence.


I don't quite follow what you mean by "base case...." , and why the FL has to change. If I read it more slowly the penny might drop.
With all these things, it depends a) what you care about and b) what you hold still, in the calculations.
It looks like you're comparing a higher pixel count image with a lower pc one, so would expect the DOF changes - the C of C is smaller.
If you compare a 24MP ff sensor with a 24MP crop one, it comes out exactly equal - that's my recollection anyway.




  
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Post edited over 2 years ago by TeamSpeed. (2 edits in all)
     
Jun 05, 2017 12:37 |  #47

Taking a macro subject where you shoot with the 100L on both a crop body and a FF body, once you equalize the framing in both, you will be closer with the FF, reducing your DOF. This is why crop bodies are often recommended (however correct or erroneous that reason might be) over FF for macros, since DOF is already such an issue to begin with.

However you end up with a smaller magnification on the APS-C vs FF, so it depends on what your goal is. I still use APS-C for macros, but with the resolution of the 5D4, I have been doing more with it due to better high ISO, and what looks like better detail rendering. I plan on now working with lighting where I have more macro lighting at the plane of the lens, this will help more than worrying about APS-C vs FF, for my needs anyways. I just haven't yet figured out what system or modifiers to start using.

http://www.bobatkins.c​om …/format_vs_macr​o_dof.html (external link)


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Archibald
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Jun 05, 2017 12:51 |  #48

Chris.R wrote in post #18371530 (external link)
I think you must have done something I wouldn't, in your maths :)
Better brains than mine have shown equivalence.

I don't quite follow what you mean by "base case...." , and why the FL has to change. If I read it more slowly the penny might drop.
With all these things, it depends a) what you care about and b) what you hold still, in the calculations.
It looks like you're comparing a higher pixel count image with a lower pc one, so would expect the DOF changes - the C of C is smaller.
If you compare a 24MP ff sensor with a 24MP crop one, it comes out exactly equal - that's my recollection anyway.

To have the same picture, the framing at the subject has to be the same, and to have the same perspective, the subject distance needs to be the same. These parameters can be diddled with the magnification and focal length. For a good match, we need to have a (fictional) 124mm lens on the FF. If we are viewing the same image from both formats, then the CofC will be proportional to the sensor size. Here are my calculations, for your scrutiny.


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Jun 05, 2017 12:58 |  #49

TeamSpeed wrote in post #18371541 (external link)
Taking a macro subject where you shoot with the 100L on both a crop body and a FF body, once you equalize the framing in both, you will be closer with the FF, reducing your DOF. This is why crop bodies are often recommended (however correct or erroneous that reason might be) over FF for macros, since DOF is already such an issue to begin with.

Shooting distance does not affect DOF if the framing is constant. Only aperture does.

Here is the comparison with the same lens. No difference really, just a perspective change.


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Jun 05, 2017 13:11 |  #50

Chris.R wrote in post #18371530 (external link)
I think you must have done something I wouldn't, in your maths :)
Better brains than mine have shown equivalence.

I don't quite follow what you mean by "base case...."

By "base case" I only meant that I selected an aperture and magnification for the crop body, and calculated these parameters for the FF body.


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Chris.R
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Jun 05, 2017 13:23 as a reply to  @ TeamSpeed's post |  #51

I'm in that camp that says that doesn't hold either.

If you look at Lefkowitz standard formula for macro DOF,
2*CoC*f*((m+1)/(m*m))
where f is what the lens has marked on it, the only parameters are CoC (directly related to pixel size) and magnification.
Nothing about proximity or FL.


Bob Atkins decided to make the f number on the lens fixed. It seems natural, but why? Just change the aperture if you want a different DOF. The POINT is that the limit is diffraction, which you find you hit sooner with the smaller sensor. On the larger sensor camera, you can afford to use a smaller aperture. It's the effective aperture which kills you sooner, with smaller pixels/sensors. M is higher so it does look as though it should work out the other way, which is perplexing.
If you pick some set of things you want to fix, you determine the outcome.
It's if you ask which format at the limit, gives you more DOF, say on a print of the same size, of the same field of view on subject, you find they're the same.

If you do much stacking at highish magnifications, it forces your brain round all the parameters - and takes you back to where you started! The problem with smaller pixels, ends up being one of getting lenses which perform well enough at widest apertures.
If I can find the spreadsheet I'll post a screenshot.
Most of this stuff was worked out, pulled together or made-sense-of, by Rik Littlefied at photomacrography forum.




  
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Jun 05, 2017 13:32 |  #52

Chris.R wrote in post #18371590 (external link)
... CoC (directly related to pixel size) ...

The circle of confusion is usually defined in terms of viewing a finished print at standard conditions, and has nothing to do with pixel size.

But we are all free to select a CoC that is different, to suit our own purposes ... but it would help to state those purposes!


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Jun 05, 2017 14:18 |  #53

Archibald wrote in post #18371445 (external link)
FF or crop is an interesting question for macro, especially when considering the 5DS with its high megapixels. I decided to do a (theoretical) comparison. To compare these formats, one has to decide on some premises, or things get real confusing. Here are my premises for this exercise.
  • Crop vs FF
  • Equal pixel pitch
  • Same picture (equal framing, perspective, and DOF)
  • Base case focal length of 100mm and magnification of 1 for the crop sensor.

In this comparison, the FF would need a focal length of 124mm and a magnification of 1.6x to match the crop picture. To get equal DOF, the FF would need f/13.8 vs f/11 (marked) for the crop body. As you suggest, the effective aperture would be a lot smaller for FF.

The FF would end up with almost double the Airy diameter, meaning that diffraction is worse and its effective resolution would be significantly less than for the crop case. Conclusion: the crop format (for the stated premises) has a significant advantage.


That one had me head-scratching for a while...

CASE 1: With FF if I mount a 100mm lens and get a 1:1 image, I frame a subject area which is 24mm x 36mm ; with APS-C if I mount a 100mm lens and get a 1:1 image, I frame a subject area which is 15mm x 22.5mm ; if both cameras had same pixel count (e.g. 4000 pixels) vertically, both cameras would put the same number of pixels on the same subject area, so resolution is identical! Erroneous analysis removed...
For example, if my subject was 15mm tall, at 1:1 in FF or APS-C the subject is IDENTICAL in size on the sensor at the same pixel pitch, and only the total area (around the subject) is larger on FF.
With FF if I mount a 100mm lens and get a 1:1 (1X) image, I frame a subject area which is 24mm x 36mm ; with APS-C if I mount a 100mm lens and I frame the subject area (which is 24mm x 36mm) onto a 15mm x 22.5mm area sensor, the subject is imaged at 0.6X.
If both cameras had same 4000 pixels vertically, both cameras would put the same number of pixels on the same image area, so subject resolution ought to be identical, when considering the sensor alone, but this is NOT considering 'the whole picture' so to speak...!
But the lens is NOT delivering the same line-pairs per millimeter at subject magnification at 0.6X on APS-C as it does at 1X to the FF sensor. A lens which delivers 100 l-p/mm on the sensor delivers 2400 l-p total resolution to FF sensor, but delivers only 1500 l-p total resolution to the APS-C sensor. With with equal subject area in each frame, the FF sensor is delivering 60% more resolution even though both sensors capture with the same 4000 pixels vertically in the shot.
...of 2400 line-pairs delivered to 4000 pxiels vs. 1500 line-pairs delivered to 4000 pixels; FF wins.



CASE 2: With FF if I mount a 100mm lens and get a 1:1 image, I frame a subject area which is 24mm x 36mm ; with APS-C if I mount a 100mm lens, and I frame a subject area which is 24mm x 36mm, and get a 0.6:1 image; if both cameras had sensors with same pixel pitch, let's assume 240 pixels per millimeter...

With the FF camera I image a 24mm tall subject at full size at 1X, with 240 pixels/millimeter, the subject is 5760 pixels tall; with the APS-C camera I image the 24mm tall subject at 0.6X into a 15mm tall sensor space, so the subject is only 3600 pixels tall. Subject resolution is 60% better with the FF image than with the APS-C image, considering only pixel count.
Bring lens resolution back into the discussion...if I have 100 line-pairs/millimeter at the sensor, it delivers 2400 l-p total resolution to FF sensor, but delivers only 1500 l-p total resolution to the APS-C sensor.

2400 l-p projected to 5760 pixels on FF vs. 1500 l-p projected to 3500 pixels on APS-C...2.4 pixels per line-pair on FF vs. 2.33 pixels per line-pair on APS-C; FF wins (barely)

My results are the complete opposite from Archibald's analysis. Somebody else will need to come up with the tie-breaker analysis.


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Chris.R
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Jun 05, 2017 14:40 |  #54

Archibald wrote in post #18371604 (external link)
The circle of confusion is usually defined in terms of viewing a finished print at standard conditions, and has nothing to do with pixel size.

But we are all free to select a CoC that is different, to suit our own purposes ... but it would help to state those purposes!

Ah, well I'd reject the old-fashioned idea about some fraction of picture width, which came from film days. If your lens is good enough then resolution is determined by pixel size, yes? It's a different game now. They used to say, what was it, 1/1500th of the frame width? It depends how many pixels you want per CoC, but you could resolve 1500 blobs wide with, say 4000 pixels wide. Let's stop at 11MP then! The 32┬Ám CoC above is about seven pixels wide for a 5DSR :-(

I haven't digested your other posts, but
"to have the same perspective, the subject distance needs to be the same. " It's Entrance Pupil distance. Some of mine are infinitely far away. (Telecentric). As you go closer of course with a "simple" lens, extending it does mean you "lose" perspective. If you're stacking then perspective can go to hell anyway. Or of course you change it in post by shrinking the frames how you want.

A thought - if you're at 1:1, edge of diffraction at f/5.6 or so, then you get (DX, 24MP, 2.5 oixels to CoC) about a quarter millimeter in focus. So if you aren't stacking, (or tilting!) any "perspective" showing is by definiton OOF. I'm not sayig that makes a "Bad" picture, but it doesn't make a lot of sense to speak of DOF.

What I think (not 100% sure) DOES happen is what I mentioned above - the oof stuff is MORE oof with the larger sensor, so you get a more usable image with the smaller sensor. That's probably more important more often than absolute resolution.

Some thinkers on the subject speak of "Equivalent Cones of light" - from subject to entrance pupil. That one does make sense for keeping your noodle on what's going on, but I do think that most of the rules of thumb are very unreliable. They so often miss out or assume something they shouldn't.




  
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Chris.R
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Jun 05, 2017 14:46 as a reply to  @ Chris.R's post |  #55

WIlt:

CASE 1: With FF if I mount a 100mm lens and get a 1:1 image, I frame a subject area which is 24mm x 36mm ; with APS-C if I mount a 100mm lens and get a 1:1 image, I frame a subject area which is 15mm x 22.5mm ; if both cameras had same pixel count (e.g. 4000 pixels) vertically, both cameras would put the same number of pixels on the same subject area, so resolution is identical!

No, it's a different subject area. You'd have more on-subject resolution with the Crop sensor.
One resolves 15/4000, the other 24/4000.
Assuming the lens can do it, the sensor is't diff limited... holding still, ...

Am I missing something?




  
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Jun 05, 2017 16:00 |  #56

Archibald wrote in post #18371604 (external link)
The circle of confusion is usually defined in terms of viewing a finished print at standard conditions, and has nothing to do with pixel size.

But we are all free to select a CoC that is different, to suit our own purposes ... but it would help to state those purposes!

^^^

The DOF on a 20D is not different that it is on a 7DII! although the pixel sizes are quite different (1.57x difference)


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Jun 05, 2017 16:13 |  #57

Chris.R wrote in post #18371676 (external link)
WIlt:

No, it's a different subject area. You'd have more on-subject resolution with the Crop sensor.
One resolves 15/4000, the other 24/4000.
Assuming the lens can do it, the sensor is't diff limited... holding still, ...


Yeah, you are...a correct analysis from me for Case 1!
Am I missing something?

I think my brain skipped a beat (or I must have had low blood sugar), let me try again ...CASE 1

  • the subject was at IDENTICAL MAGNFICATION (at 1:1) so the same 10mm of subject surface would fall onto the same 10mm of sensor for both cameras
  • if the sensors both had SAME PIXEL COUNT (e.g. 4000 pixel height), 10mm of subject would be captured with 1667 pixels on FF, or with 2667 pixels on APS-C
  • If we have 100mm lens on both bodies, and it delivers 100 line-pairs/millimeter, in both cases there are 1000 line-pairs of detail falling onto 10mm of sensor


...so [1667 pixels capturing 1000 line-pairs on FF] vs. [2667 pixels capturing 1000 line-pairs on APS-C].
The APS-C camera in this case has sufficient pixels to exceed the Nyquist in the capture of the lens' resolution, while the FF falls short of that need and leaves some lens resolution uncaptured.

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Chris.R
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Jun 05, 2017 16:16 |  #58

Wilt wrote in post #18371736 (external link)
^^^

The DOF on a 20D is not different that it is on a 7DII! although the pixel sizes are quite different (1.57x difference)

I'd disagree there, too. My take: You can choose whatever CoC you want, down to the minimum the sensor can manage. for a 1000px web image it can be big.
If you want to be able to walk up to a monster print, you'd better make is as small as possible.

We all see these things differently!




  
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Jun 05, 2017 16:28 |  #59

Chris.R wrote in post #18371748 (external link)
I'd disagree there, too. My take: You can choose whatever CoC you want, down to the minimum the sensor can manage. for a 1000px web image it can be big.
If you want to be able to walk up to a monster print, you'd better make is as small as possible.

We all see these things differently!

Certainly you see it differently from a program written in an Excel worksheet by a POTN member, to calculate DOF of different format

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/Principles/macro%20DOF_zpsf6qudsm0.jpg

...nowhere is there an input parameter for grain size of film or pixel pitch of digital

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Chris.R
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Jun 05, 2017 16:40 as a reply to  @ Wilt's post |  #60

Yes I do!

In the spreadsheet I use most I put in the pixels per CofC I want, to give the DOF for stacking. There is a very small benefit going smaller than about 2.5, not usually worth it. A small image might warrant a 5 or 10.


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