Aperture diffraction?

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Archive 2007 · Aperture diffraction?

Ken Sato
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p.1 #1 · Aperture diffraction?

I guess this is my first post after reading this site for a while!

After doing a bunch of research and narrowing down my choices I picked up a Canon 70-300 F4-5.6 IS. I was testing it out when I noticed that at F22 70mm I am getting fuzzy images, compared to bigger apertures. At 300mm F22 vs. F5.6 I'm not noticing the same fuzziness. Do you think this is just due to aperture diffraction? Or perhaps the tripod is giving way a bit to the weight of the lense. I tried to tighten everything down on the tripod though. Feel free to chime in with anything else about these test shots since I'm a beginner. Thanks!

Overview of the indoor shot I was testing with:

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All crops at 100%, tripod, IS turned off, shot as jpeg's.

70mm ISO 400 F5.6 1/15sec

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70mm ISO 400 F22 1sec

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70mm ISO 400 F32 2sec

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300mm ISO 400 F5.6 1/13sec

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300mm ISO 400 F22 1.3sec

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Jan 10, 2007 at 08:01 AM

millsbury
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p.1 #2 · Aperture diffraction?

Diffraction

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Jan 10, 2007 at 08:58 AM

Monito
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p.1 #3 · Aperture diffraction?

Welcome to the FM forums, Ken Sato (first post).

Some lenses are naturally less sharp at f/22 or f/32. I think you are seeing some minor diffraction effects, but mostly that the lens is not optimized for 70mm f/22.

Jan 10, 2007 at 09:12 AM

SpeedyGonzales
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p.1 #4 · Aperture diffraction?

Your 70mm f/22 image actually looks shaky in the up-down direction. Did you use self-timer or remote and mirror lockup?

Diffraction effects for a circular aperture is only dependent on f-stop, not focal length, but I don't know how a non-cricular aperture effects things.

Jan 10, 2007 at 12:47 PM

vyanush
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p.1 #5 · Aperture diffraction?

On a crop DSLR at about f/11 you are "welcome to difraction" area. It does not directly depend on FR, but if you use same scene, at 300mm details look ~4 times larger than at 70mm. Thus subjectively you see less "blurring" at 300mm than at 70. Nevertheless, to my eyes it is still there at f/22.

Of course, subject to tripod&MLU usage and IS SWITCHED OFF.

Jan 10, 2007 at 01:43 PM

gfiksel
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p.1 #6 · Aperture diffraction?

Ken,
To do this comparison correctly you want to move away with the longer lens to keep constant framing. That is the relative size of the image should be same.

If you look at your 300mm shots you can see that the f/22 shot has more diffused edges but it just less noticeable in comparison to the 70mm shots because of a larger image.

All details look better at a larger magnification so to compare different focal lengths you want to keep the magnification the same.

PS. Sorry, cross-posted with Vladimir. I guess we were typing at the same time

Jan 10, 2007 at 01:53 PM

Gino02GT
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p.1 #7 · Aperture diffraction?

Pixel size determines when you'll see these effects. On my 20D/30D I would see it after f/11. On my 5D, I can take that to f/16. Little P&S cameras can diffract after f/2.8 or f/4.....ouch.

Jan 10, 2007 at 02:56 PM

Ken Sato
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p.1 #8 · Aperture diffraction?

I used the self-timer. I had a feeling it might be due to the 1-2sec Tv and the weight of the camera making it move on the tripod. I wasn't able to shoot at a good ISO to take the picture at a faster speed to help figure out if it was tripod movement, but this is what it looks like at 70mm at 1600 ISO. I think I need to get outside to take some more test shots but it's wet, slushy and ugly outside.

Thanks for everyone's feedback so far!

From left to right:
F4 1/80
F5.6 1/40
F8 1/20
F13 1/8
F16 1/5
F22 0.4
F32 0.8

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SpeedyGonzales wrote:
Your 70mm f/22 image actually looks shaky in the up-down direction. Did you use self-timer or remote and mirror lockup?

Diffraction effects for a circular aperture is only dependent on f-stop, not focal length, but I don't know how a non-cricular aperture effects things.

Jan 10, 2007 at 07:28 PM

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