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03-19-2010, 05:53 PM   #1
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DOF and medium format

After browsing some medium format beauty images like this:
NikonCafe.com

it looks like not that much of the head/neck is in focus...only the face. And this was shot at f/11.
And according to LL, lens diffraction starts at f/11 on a P45 back which is a 1.1x crop MF sensor.

On MF, what do you do for beauty shots if you want the entire neck/shoulders in focus as well? This seems like the same problem you have if you move to a FF sensors from APS-C...lots of weird tradeoffs in DOF vs. diffraction...

03-19-2010, 07:31 PM   #2
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QuoteOriginally posted by kenyee Quote
After browsing some medium format beauty images like this:
NikonCafe.com

it looks like not that much of the head/neck is in focus...only the face. And this was shot at f/11.
And according to LL, lens diffraction starts at f/11 on a P45 back which is a 1.1x crop MF sensor.

On MF, what do you do for beauty shots if you want the entire neck/shoulders in focus as well? This seems like the same problem you have if you move to a FF sensors from APS-C...lots of weird tradeoffs in DOF vs. diffraction...
It says I need a log on.
Diffraction is much over rated as a problem. It exists, and can be seen if you shoot test targets, but in reality, it isn't a big deal in general photography.
I stop down to the stop I need to get what I want in focus. If this causes some diffraction, so be it. I get what I want in focus, and that trumps the other considerations.
03-19-2010, 08:42 PM   #3
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It's not like diffraction means that once you stop past some magical number your images turn to mush. Most lenses perform ideally a stop or two down from wide open, and diffraction can make the image slightly softer at smaller stops; that does not force us to shoot at some ideal aperture--disregarding artistic intent--just because it's the best one on paper.

Interestingly, diffraction limits seem to move in lock step with DOF changes, so I wonder (though I haven't bothered to look at it from a purely theoretical standpoint as I prefer to spend my camera time taking pictures; what a concept) if there's ultimately no difference between formats. APS format hits diffraction issues sooner, but FF gives you less DOF so you have to stop down more, giving up the light gathering advantage of the bigger sensor to get the same DOF and then you start seeing diffraction creep in much the same as on the APS sensor...
03-19-2010, 10:12 PM   #4
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QuoteOriginally posted by kenyee Quote

it looks like not that much of the head/neck is in focus...only the face.
I can only guess what the picture looks like because of your link. But maybe that was the photographer's intention. It is a common thing to do. The face and eyes is all that needs to be in focus; otherwise, you get that small format point-n-shoot look where there is always infinite depth of field whether you want it or not.

03-20-2010, 03:36 AM   #5
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I can't access the photo sample either, but I'm familiar with the look.

One thing to remember about diffraction is that the size of the format is a variable in this situation, where the smaller the frame the sooner diffraction starts to become bothersome.

A good way to think of this is this: the smaller the format, the closer together the line pairs have to be, to get the same resolution when the image is viewed at a large size. Let's say you need to have 1000 line pairs captured in order to have a sharp, detailed photograph that covers the entire film area. Those 1000 line pairs do not need to be very closely packed with a large format camera, you need to pack them into a slightly smaller area with 120 film, and pack them even closer together with 35mm, closer yet with APS-C, and closer still if you're shooting with a Minox... Of course, if you only take the area of film equal to a 35mm frame from a larger format, that smaller area needs to contain all 1000 line pairs...

This is the medium format advantage. The lens does not need to resolve as much as a 35mm lens in order to seem sharp, or put another way, a lens that's as good as a decent 35mm lens will be stellar on 120 film. The captured picture area also does not require as much enlargement as a 35mm frame.

So diffraction, which begins to lower contrast between the line pairs, becomes a consideration when these line pairs have to fit into a smaller area - and thus have to be closer together. When the line pairs have more area, and can be further apart on the film, it takes more diffraction to begin to blur the area between them.

I hope I explained this well...
03-20-2010, 07:08 AM   #6
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QuoteOriginally posted by Nesster Quote
I hope I explained this well...
Yep, you did. Conceptually, you have the same idea as pixel DPI except applied to lenses. The lenses don't need as high DPI on larger sensors because the large sensors don't have has much DPI.
The guy also linked to the full size image in that post which has a shrunken copy of this:
http://www.polodigital.net/images/SandyM/Sandy035f.jpg

I've seen APS-C beauty images and they seem to more consistently have the neck/shoulders in focus. It could be this was done deliberately, but I thought beauty photogs tried to make sure things were as sharp as possible everywhere, so they would use the diffraction limit f stop when shooting. I've done jewelry photography at f/22 on APS-C but that gets shrunk down to web resolution so it doesn't matter nearly as much
03-20-2010, 07:38 AM   #7
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Diffraction is a theoretical limit which reminds us that lenses are practical devices and never reach the theoretical limits. In practice you won't notice diffraction until it "catches up" with the other lens defects. Check mtf charts of particular lenses you're interested in to see how they actually perform - all factors considered.

Also, the obvious approach to get more DOF when you can't stop down further is to use a shorter focal length.
03-20-2010, 08:06 AM   #8
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QuoteOriginally posted by kristoffon Quote
Also, the obvious approach to get more DOF when you can't stop down further is to use a shorter focal length.
Not true. Focal length does--contrary to popular belief--NOT directly affect DOF.

Distance, however, does.

03-20-2010, 08:16 AM   #9
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QuoteOriginally posted by pingflood Quote
Not true. Focal length does--contrary to popular belief--NOT directly affect DOF.

Distance, however, does.
I wonder if that is true... if you look at the DOF calculation, focal length, among other factors, is in the equation. Sorry, this is beyond me... I am still learning.
03-20-2010, 08:58 AM   #10
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QuoteOriginally posted by pingflood Quote
Not true. Focal length does--contrary to popular belief--NOT directly affect DOF.

Distance, however, does.
Well, my DOF scale on my lens is lying to me, dammit. Here's what it is saying:

150mm lens focused to 3m at f16: ~2.7m to 3.5m
60mm lens focused to 3m at f16: ~1.7m to 15m

I'm going to sue. Do you mean moving closer to fill the frame equally with the shorter focal length?

Last edited by tuco; 03-20-2010 at 09:05 AM.
03-20-2010, 09:36 AM   #11
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QuoteOriginally posted by kristoffon Quote
Also, the obvious approach to get more DOF when you can't stop down further is to use a shorter focal length.
If you're doing portraits, you don't want to use short focal lengths because of perspective distortion. E.g., for head/shoulders shots, the 77Ltd works great (110mm FF equiv). Get in any closer than that, you get big noses, weird ears, etc...
03-20-2010, 11:27 AM   #12
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QuoteOriginally posted by pingflood Quote
Not true. Focal length does--contrary to popular belief--NOT directly affect DOF.

Distance, however, does.
I think you're mistaken. Somehow I can't quite get enough blur of my 15mm f/4 compared to my 77mm f/4 even whem shooting pretty close.

And of course, with a shorter focal length, distance would decrease to mantain the same composition.
03-20-2010, 11:36 AM   #13
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QuoteOriginally posted by kenyee Quote
If you're doing portraits, you don't want to use short focal lengths because of perspective distortion. E.g., for head/shoulders shots, the 77Ltd works great (110mm FF equiv). Get in any closer than that, you get big noses, weird ears, etc...
77 mm (and 85) are the classic portrait focal lengths for film. On aps-c 50mm would work out to be the equivalent. Such is the DA*55 the official portrait lens on the lineup today.

It all depends on the particular situation and what you can get away with.
03-20-2010, 01:49 PM   #14
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QuoteOriginally posted by tuco Quote
Well, my DOF scale on my lens is lying to me, dammit. Here's what it is saying:

150mm lens focused to 3m at f16: ~2.7m to 3.5m
60mm lens focused to 3m at f16: ~1.7m to 15m

I'm going to sue. Do you mean moving closer to fill the frame equally with the shorter focal length?

Yes, sorry for not stating it better; I meant that once you move closer/further to have the subject occupy the same portion of the frame, focal length has no real effect on depth of field. In other words, if you moved close enough with the 60mm to have the same framing as the 150mm you'd have the same depth of field.

There's a pretty good explanation here: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
03-20-2010, 03:51 PM   #15
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QuoteOriginally posted by kristoffon Quote
77 mm (and 85) are the classic portrait focal lengths for film. On aps-c 50mm would work out to be the equivalent.
On film, for waist up shots, yes the 77 is good for that. I mentioned head/shoulders on crop because 77 is tighter on APS-C...
It's mainly subject to distance that causes/prevents perspective distortion...
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