Heres a collectiom of tips from the discussions held some time ago on f-stops. Ive put the most recent at the bottom.
(From Ben Lin) The 100mm macro from Canon is superb from f/2.8 to f/22. I shot some flowers for stock at f/32 and didn’t even bother submitting them because of the crappy quality. The Canon 70-200 is awesome, no matter what version.
(From Ben Lin) When I said that the Canon 100mm macro was crappy at f/32, I was exaggerating a bit. Allow me to clarify: from f/2.8 to f/22, I can count the hairs on a bee’s back. At f/32, the hairs start to get a little fuzzy. I can still make them out, but there is a noticeable image quality drop-off. Having been spoiled by what it can do on the wide open range, I didn’t want to bother submitting the f/32 version here. Although the DOF was increased dramatically.
It’s kind of like shooting with the (Canon or Nikon) 70-200mm f/2.8 at f/5.6 and then shooting with the kit 18-55mm f/3.5-5.6 lens at f/3.5. Can you get great photos with the kit lens? Definitely. Are they going to be tack sharp like the super-zoom? Not even close. Have I sold stock images with the kit lens? Yes, but I won’t tell you which ones.
(From dcdp) Once an F2.8 lens goes past about f13 it begins to hit diffraction limits in the physical glass structure. It physically cannot be as sharp as it was at f8. The faster the glass, the earlier you hit the diffraction limits. You may not be able to tell the difference initially but sharpness drops off after a certain point purely by the laws of physics.
Here are a couple of pages on the topic:
If you want to see it in action looks at the detailed analysis of your favourite lenses here.
(From esp imaging – answering dcdp) I thought that diffraction effects were strongly related to (effective) aperture, and hence focal length?
Diffraction effects short focal lengths more than long focal lengths at the same f stop, because the actual aperture is smaller, and hence diffraction effects are larger.
i.e. a 220mm lens at f/11 has an effective aperture of 220mm/11 = 20mm, whereas (say) a 22mm lens at f/11 has an effective aperture of only 2mm, and hence massively larger diffraction effects.
So diffraction from your 100mm lens at f/16 will be a lot less than from a 24mm wide angle lens at f/16, possibly even less than the 24mm lens at f5.6 or so.
(From Leviticus)- (answering esp imaging) which is why the 105mm nikkor 2.8 is such a beast at smaller apertures, even totally closed down (which it needs to be at 1:1) they are still as sharp as a kit lens. It’s a DOF v sharp payoff.
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