Sharpest two stops down....or not?

rdenney wrote in post #2107231
Rather than provide links to online lens tests, I would rather address the underlying basis for that rule of thumb. That way, instead of trying to verify a rule, you'll know how to make your own rules.

But remember that the optimum aperture isn't useful if it forces you to use a shutter speed that allows motion blur, or if it lacks sufficient depth of field.

Rick "who thinks other influences on aperture are more important" Denney

Now, I agree with that, Denney.
However, if you have some aperture latitude in the field, the lens optics principles are as useless as a third tit. Unless one knows/remembers the lens sweet range, one should stay in the vicinity of the generic sweet spots....like f/4.0-f/8.0 or some such.

Petkal who thinks simple heuristics rules.

check out photozone.de

Yep, the data supports it! The 135L holds it's sharpness edge to edge and throughout it's focal range though Damn impressive lens

Tee Why wrote in post #2108669
check out photozone.de

check out that they don't test with a full-frame camera. Good information, but note that the corner information isn't there.

Yeah, they're consistent with the 350D... But it would be nice to update everything with a 1Dxx or 5D maybe.

JNunn wrote in post #2108408
Shooting at f/2.8 or lower actually is a bit confining in that the DOF is so minimal. Let's see...not good for close portraits (unless you don't care that the ears aren't in focus while the nose is)...not too good for macro (unless your bug or flower is flat!)...not good for landscapes, etc.etc.

I guess that's why I don't find my 70-200mm f/4 or 17-40 f/4 painfully slow as do some people. I almost always need DOF and that means stopping the lens down.

I agree with what you are saying, but I would offer a bit of debate. If you use f/32 or f/45 on an APS sensor, your ability to enlarge will be greatly hampered by the effects of diffraction. An 8x enlargement of 6x4.5 medium format is about 13.5x18 inches. From the 15x23mm format of an APS sensor, it's a 5x7-inch print. If you make a 12x18 print from the 15x23 format, the effects of diffraction will be three times larger and more apparent. Fortunately, depth of field is better with the shorter focal lengths permitted by the small format, so it compensates.

I can get razor-thin depth of field in medium format using my favorit portrait lens, a CZJ Sonnar 180/2.8. At 180mm, f/2.8 is fast, even by small-format standards. Getting DOF that thin with a lens that is 2.4 times normal would require something like a 70mm/1.4 lens in APS format, or 100mm/1.8 in 35mm format. That's one reason why small formats have such fast lenses.

Another reason is that small cameras are intended for hand-held photography, particularly for reportage. Most serious landscape photographers would think of medium format as too small, and a compromise at best. (A compromise I'm certainly willing to make, heh, heh). I'll use f/45 on a 4x5 camera, but if I can't get sufficient depth of field at f/32 in medium format, I look for a different composition. In fact, I think f/32 is the smallest aperture I have in any medium format lens--most only go down to f/22.

I once did some copy work with the 10D using the 50mm/2.5 compact macro. That lens has really small apertures, and because of my copy stand lighting, I used f/22. I had to do it over--too much diffraction effect.

With a view camera, you can control depth of field with tilts, and that's something I wish was more readily available in the smaller formats.

Edit: I forgot to mention that the old photographers thought of thin depth of field as providing sharply focused eyes, slightly fuzzy nose, and out of focus ears. I can do that with the Sonnar, and with the 85/1.8. The old guys did it with f/6.3 lenses on 8x10" format, or with f/4.5 lenses on 4x5" format. I have an old Ilex Paragon 8.5"/4.5 lens for 4x5 that is an example of what was once used. Different formats have a big effect on the apertures one needs for a particular effect.

Rick "who has shot thousands of images on Kodachrome 25 and Panatomic X" Denney

Petkal wrote in post #2108490
Petkal who thinks simple heuristics rules.

The heuristic that I'm suggesting is that we practice enough with the lenses we use so that we don't have to have general rules of thumb to guide our practice. For lenses where I don't have that experience, I just use f/8, as in the old saying "f/8 and be there!" Most of the time, though, I have depth-of-field or shutter speed requirements that dictate what aperture I must use to get the effect I want. If the results are unacceptable, I cross that lens off the menu of available optics for those sorts of situations in the future.

Rick "who thinks instinctive responses based on experience are the ultimate heuristic" Denney

rdenney wrote in post #2111161
The heuristic that I'm suggesting is that we practice enough with the lenses we use so that we don't have to have general rules of thumb to guide our practice. For lenses where I don't have that experience, I just use f/8, as in the old saying "f/8 and be there!" Most of the time, though, I have depth-of-field or shutter speed requirements that dictate what aperture I must use to get the effect I want. If the results are unacceptable, I cross that lens off the menu of available optics for those sorts of situations in the future.

Rick "who thinks instinctive responses based on experience are the ultimate heuristic" Denney

Gotcha....I am with ya now.

rdenney wrote in post #2111161
The heuristic that I'm suggesting is that we practice enough with the lenses we use so that we don't have to have general rules of thumb to guide our practice. For lenses where I don't have that experience, I just use f/8, as in the old saying "f/8 and be there!" Most of the time, though, I have depth-of-field or shutter speed requirements that dictate what aperture I must use to get the effect I want. If the results are unacceptable, I cross that lens off the menu of available optics for those sorts of situations in the future.

Rick "who thinks instinctive responses based on experience are the ultimate heuristic" Denney

That makes great sense. I should create like a list of questions I need to answer before choosing my camera settings like:

What are the lighting conditions you are shooting with?
Is what you are shooting in motion? If so, is it in motion very fast or slow?
Are you trying to isolate your subject from your background?
Do you want to freeze motion?

i find my 17-55 lens sharp at f/3.2 to about f8 or so... after that, you can really tell that it's not as sharp. not saying it's bad, but there's no real reason to shoot from f/9 - f/22 unless you are really looking for some kind of motion blur control.

rdenney wrote in post #2111122
ffect.

Rick "who has shot thousands of images on Kodachrome 25 and Panatomic X" Denney

Excellent description! I think(?) my Zeiss 40mm Distogon had f/45, I know my 50mm had f/32. You're also right about the change in perspective in dealing with the different formats and hand holding versus tripod mounted.

Again, excellent description!

JNunn wrote in post #2113184
Excellent description! I think(?) my Zeiss 40mm Distogon had f/45, I know my 50mm had f/32.

It's my 180/2.8 and 300/4 Sonnars that have f/32. That's effectively a 5.6mm and 9.4 mm aperture, respectively. But f/45 on a 40? That would be .9mm, which is a tiny, tiny aperture. I would expect lots of diffraction, not to mention the difficulty in making an iris accurately for a hole that small. I'm impressed by the engineering that would be required (and think that Zeiss Oberkochen might be one of the few factories that could pull it off), but I think I would avoid it, heh, heh.

My 30mm Arsat fisheye, 45mm Mir and 50mm Flektogons only go down to f/22. The Mir and the Fleks are old-fashioned retrofocus designs that need to be stopped down to perform well. I don't make really big prints, though. If I did, I'd be having to pull those Super Angulons out all the time.

Come to think of it, I'm going to check to see how small the aperture gets on my 47mm Super Angulon. It might indeed stop down that far.

Rick "who needs to get back into large-format photography" Denney