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:

Diffraction

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

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.

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.

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.

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

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.

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