Diffraction vs Large Depth of Field


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Dec 28, 2008
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#1
Hi guys, need some input and advice on this question I have.

We know that lenses are sharpest at f/8-f/11, and that depending on the lens there runs a risk of diffraction after f/11. This would mean that due to the 'dispersing light' effect it may cause some blur to images after f/11.

However, sometimes stopping down to apertures like f/16 and f/22 (or even f/32) is required due to a large depth of field required. So to ensure that for example the foreground and background of my landscape shot is nicely in focus, I would have to go for f/22.

So from what I understand, the question now is which is the most ideal situation. Due I stick to f/8-11 to prevent diffraction, or do I just go for f/22 so that I get the depth of field? Because I see it, either way I lose sharpness. If I stick to f/8-11 my faraway foreground could lack DOF, but if I go f/22 diffraction happens. Hmm ... ??

Thanks.
 

zac08

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#2
Actually at landscape terms of wider lenses, you actually have very good DOF even with relatively large apertures.

So there is not much issues when shooting at f8 to f11 on those. And if you are using a tele lens to isolate a certain portion of the landscape, then you won't need to worry about the DOF issue as it'll be isolated to one area anyway....
 

calebk

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#3
How do you know that at f/11, you won't get sufficient depth of field, and that stopping down to f/22 in your particular situation would render you the depth of field you need?
 

Dec 28, 2008
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#4
How do you know that at f/11, you won't get sufficient depth of field, and that stopping down to f/22 in your particular situation would render you the depth of field you need?
oh i posed this question because on reading a book, i've realised there was no mention of the problem of diffraction at all. all that was stated is that f/8-11 gives sharpest. but the thing that got me confused was that despite saying that, and when examples of landscapes shots (huge distance between foreground buildings and background buildings) were shown, i realised the author used mostly f/22 apertures so as to attain large DOF.

i must say i havent really tried it to compare, but would like to hear from others.
 

giantcanopy

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#5
I usually shoot ard f11 - f16 or even f22 occassionally when needed especially to keep some of the lens corners sharp as well for landscapes.

Ryan
 

Octarine

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#7
oh i posed this question because on reading a book, i've realised there was no mention of the problem of diffraction at all. all that was stated is that f/8-11 gives sharpest. but the thing that got me confused was that despite saying that, and when examples of landscapes shots (huge distance between foreground buildings and background buildings) were shown, i realised the author used mostly f/22 apertures so as to attain large DOF.
It seems that the author took these pictures either on film or Full Frame DSLR where the pixel area is bigger (size of the one pixel). In such cases diffraction will come in later then on a cropped sensor DLSR where the pixel area is smaller. The lens itself (focal length, type) does not affect diffraction, only the aperture opening.
More here: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
Small sensor cameras (PnS and crop sensor) have a longer DoF by nature. So with the same lens (focal length) and the same aperture settings a PnS will have larger DoF then a crop sensor DSLR. FF will be even shorter. In return you don't need to use f/11 and beyond to have sufficient DoF. You can use DoF calculators to check this. More details here: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
 

Dec 28, 2008
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#8
ahh .... thanks guys for the replies, and Octarine for the useful links!!
 

night86mare

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#9
most of the time, f/16 is more than sufficient.

when shooting landscapes, i usually stop down more to extend exposure timing while keeping low iso, rather than use it for depth of field. this also applies for telephoto perspectives.

f/22 is still fine to be honest, people like to pixel peep, at the end of the day, web size photos look ok, printouts look ok, no one is going to ask you, did you shoot at f/22 and tell you how soft the picture is. sometimes, the proper sharpening process done when processing the photo counts just as much as what mumbo jumbo diffraction. if you need to extend the shutter speed, don't worry so much about it.

the only exception i can think of is, when you are shooting something pretty close to your camera at ultra wide angle. in such a case, an alternative is to "focus stack", just use a tripod, take a photograph at f/11-f/16 focusing on the thing which is close, assuming it falls within minimum focusing distance for your lens.. then adjust manually to the hyperfocal distance and shoot at the same depth of field. you can then layer these two photographs in photoshop and erase to create a photograph with everything sharply in focus.
 

Kit

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#10
Most of the time, I don't go beyond f11 but there are instances which I need to, especially when you need to cover the foreground near you. Diffraction is at times blown out of proportion by people who look at photos by the pixels. The problem with lack of DOF is usually more pronounced than quality deterioration caused by diffraction, on prints. So stop down when you need to but you don't have to stop down beyond what's necessary.
 

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