gdanmitchell
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I keep things simple. My general “rules of thumb” are more or less as follows:
1. If DOF isn’t an issue — say with a shot where all elements are in a relatively flat plane parallel to the sensor — I’ll just use whatever aperture I think will give me more or less the sharpness image overall. That would likely be close to thee diffraction-limited aperture, though the capabilities of your lens (corners sharp, etc.) might offset things a bit.
2. If I want the narrowest possible DOF I’ll likely just open up all the way… though often something a bit less than narrowest makes more sense — so let’s just say I open up to get the effect I want. Might I lose a bit of sharpness in the center? Could be. Does it make much difference? Rarely. Is corner sharpness loss at the largest aperture a bit deal? Rarely, if your shot is about contrasting the relative sharpness of a central subject with softness of surrounding and background (and possibly foreground) elements.
3. If I need more DOF I’ll stop down to f/11 with no worries at all. You can make a very large and very sharp print from most f/11 shots even if they are technically not quite as sharp as using a larger aperture closer to the diffraction-limited aperture. I will use f/16 without a lot of concern if the extra bit of DOF is more important to the shot that the slight loss of sharpness. in the final image after post-processing. I would only very rarely use f/22, and then only if I’m willing to accept that lowered sharpness spotential.
Other stuff comes into play.
For example, using long focal lengths for things like landscape may make an aperture that is sharp enough with a shorter focal length work far less well. (The distant subjects are larger relative to close subjects, so any softness may be more visible.) Of course, the opposite may be true with very wide lenses.
In situations where I need scene elements at a very wide range of distances to be sharp, I have a couple of options at my disposal. I occasionally use a medium format zoom lens on a TS adapter. I also sometimes do focus bracketing.
That’s it. Works for me.
Finally, a reminder of something that at least some people seem to lose track of. Higher sensor resolution does not increase blur at any aperture. For example, if you set up a 16MP FF camera and a 60mp FF camera side by side, put your lens on teh 16MP camera and made an exposure at some aperture, and then moved the lens to the 60MP camera, left the lens at the same aperture, and made an exposure with it… and then printed both images at the same size… they would have…
… exactly the same amount of diffraction blur. There is no more (or less) blur in either case.
Diffraction is an optical thing, not a sensor thing. We could say three things about this experiment:
1. As above, the “size” of the diffraction will be identical in both cases.
2. The higher resolution camera, while not producing any more diffraction, will record the lens diffraction more accurately.
3. In some cases, when you can use a very good lens at an aperture that is larger than the diffraction-limited aperture on teh 16MP example, and close to or equal to the diffraction-limited aperture on the higher MP camera, the higher MP camera has an advantage of a bit more potential sharpness.
OK, one more thing. Regardless of all that, there are other potential pluses from the higher MP camera, too. For example, it might give you slightly smoother gradients. The “grain size” of any noise will be smaller and potentially a bit less visible. If pixelation becomes an issue with a (very!) large print, it will occur at a somewhat larger size with the higher resolution sensor.
Whew…
Apologies tor the long post, but some things aren’t as simple as a one-sentence post. There are things that interact, there are misconceptions, there are pluses and minuses to choices. Photographers are always weighing these things.
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cheers.