gdanmitchell
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mdude85 wrote:
It's a bit of a paradox that better technology to more easily and quickly capture an extremely sharp image has induced a sort of fixation on sharpness among a lot of photographers.
In terms of the effect on photographers, I think there are two elements.
1. Because getting a “sharp” photograph has always been a concern (that’s, in part, why we use tripods, remote/cable releases, careful focus, appropriate shutter speeds, good lenses), “sharper” has always been seen regarded as a virtue in photography, even to the point that some of the “sharper-ness” today goes beyond being meaningful. (E.g. people who will pick one “sharpest” lens over an another very fine and quite sharp lens that test as very slightly less sharp in some way.)
2. For those who do produce large output, today we can push relatively small formats (such as full frame) far beyond what we would typically have considered back int the day. Today we (who make large prints) regularly produce beautiful prints at sizes that were the sole domain of large format film photography. For those people, the extra “sharpness” of lenses and the higher resolution of contemporary digital cameras do make a difference. (Hint: Most users are not in this category. To be blunt, those who are making photographs to share on social media, etc don’t get any benefit from the highest resolution systems, aside from a “feel good” benefit. ;-)
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Along these lines, some of the notions about aperture, diffraction blur, and depth of field that I read are… simplistic.
Years ago I bought into the believe that (on the cameras of that era in a certain format) f/8 was the “sharpest” aperture. In fact, there was a logical argument for saying that. As long as you were photographing a flat subject parallel to the film/sensor plane.
Changing the aperture to deal with DOF isn’t about getting the very sharpest measured image at some point in the frame from a given lens and format. It is about getting best getting the photographic effect you have in mind. And, going further, “sharpness” isn’t about the sharpest aperture, but about getting the visual quality of sharpness that you want in your photograph.
The examples are pretty obvious, but here you go:
1. If focus a varying distances isn’t an issue (say you re photographing a brick wall or you aren’t really concerned about absolute sharpness in front of or behind your primary subject… just use what you judge to be the sharpest aperture for your lens. That is, in part, the diffraction-limited aperture, but if you are using a lens that sharpens a bit in the corners at a slightly smaller aperture you might go there instead to bet the best overall sharpness sin the frame and the expense of the ideal sharpness at the theoretically best point on that lens.
2. If you have a subject with elements at varying distances and you want to highlight a primary subject (via lighting, position, focus, etc.) and diminish the attention on those at other distances, in addition to using lighting, color, composition (and other things) to deemphasize background (and possibly foreground) elements, using a larger aperture to limit the DOF may produce an image that is “subjectively sharper,” even though the sharpest point in the image may be objectively less sharp than if you sued the supposedly ideal aperture for that lens and format. (Yes, the perception of sharpness may trump the measurement of sharpness.)
3. If you have (as in #2) a subject with elements at varying distances, but you want to get the best focus possible on all of them (without using things like focus blending or lenses with movements), then you sacrifice some of the optimal sharpness at the “plane” of optimum focus by using a smaller aperture that visibly improves the focus on those elements at different distances. Again, while the measured sharpness of the sharpest point in the frame may diminish, the “subjective sharpness” of the image improves because (as desired here) more elements look sharp. The skeptic says, “but at f/16 or f/22 you’ll have diffraction blur!!!” Yes, you will. But you have to go beyond what the math tells you and evaluate the image to see whether that sacrifice leads to a better overall image in this context or not.
That’s a lot of words, but you can reduce the entire brouhaha down to three options:
1. If DOF doesn’t matter (and other factors permit it), just shoot close to the diffraction-limited aperture.
2. If you want to limite DOF, open up as far as needed.
3. If you want to maximize DOF close down as far as needed.
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away. “One reason Galen emphasized forward focus is that this let infinity go just a bit on the soft side, and provided an additional depth cue”.