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In photography, it seems universally agreed that you should shoot at f8 to f11—basically an aperture before light diffraction comes into play.

I've been quite confused about this for a while. Let's say I'm taking pictures of mountains that are 1km away, with a 70mm lens. According to this calculator, the hyperfocal length for this lens (on a full-frame sensor) is around 50m at f2.8, which means that practically everything beyond this will be sharp. Why then is it advised to use f8 instead of anything else like f2.8? What benefit does this bring?

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  • \$\begingroup\$ There can be a lot of objects in the range between 20m and 50m. If there are none, just take 2 shots next time and and judge on the result yourself. Possibly f/8 is still sharper \$\endgroup\$
    – Thomas Weller
    Commented Jun 14, 2020 at 19:51
  • \$\begingroup\$ Interesting, why would that be? Wouldn't sharpness not matter anymore beyond the hyperfocal length, since everything after the hyperlocal length is sharp? \$\endgroup\$
    – Skeleton Bow
    Commented Jun 14, 2020 at 20:04
  • \$\begingroup\$ Probably has something to do with having a catchy saying like "F8 and be there." Similar to why people become obsessive about "rule of thirds". What aperture to use depends on the camera, lens, and shooting conditions. \$\endgroup\$
    – xiota
    Commented Jun 14, 2020 at 20:49
  • \$\begingroup\$ "...it seems universally agreed that you should shoot at f8 to f11... It doesn't seem that way at all to me. There are just as many folks out there who think every image should be shot wide open at f/1.2, f/1.4, f/1.8, etc. or whatever the lens' maximum aperture is. \$\endgroup\$
    – Michael C
    Commented Jun 16, 2020 at 14:07
  • \$\begingroup\$ "... since everything after the hyperfocal length is sharp? Everything after the hyperfocal distance is acceptably sharp for intended display size and viewing distance. If the display size or viewing distance changes, so does the hyperfocal distance. Everything beyond the hyperfocal distance is not equally sharp. \$\endgroup\$
    – Michael C
    Commented Jun 16, 2020 at 14:12

3 Answers 3

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Depth of field refers to the distance between the nearest and farthest objects that appear "acceptably in focus"; it does not convey information about absolute sharpness in the resulting image. All lenses suffer aberrations of various kinds, and these aberrations tend to be the strongest at the perimeter of the lens, where they are harder to correct for. Stopping a lens down reduces the contribution to the image from these peripheral parts of the lens and thus tends to increase sharpness in the plane of focus. At very small apertures diffraction comes into play and reduces sharpness again.

For a typical small-format lens, the sweet spot that minimizes information loss occurring from both aberration and diffraction is likely to lie close to f/8, hence the "universally agreed" rule of thumb you mention. To illustrate, here is a series of 100% crops of a book cover photographed from a distance of about 0.3 meters using a 50mm lens on an APS-C sensor (the detail is about 1cm x 1cm):

f/3.5 – largest aperture of this lens. The subject is in focus but not necessarily very sharp.

f/3.5

f/8 – this is better

f/8

f/22 – smallest aperture of this lens. Again, the subject is in focus but now appears blurry because of diffraction.

f/22

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  • \$\begingroup\$ So it makes a difference, but not that much? What about lenses which are considered (practically) "sharp wide open?" I assume those lenses would be fine to shoot wide open, if the subject is far enough away? \$\endgroup\$
    – Skeleton Bow
    Commented Jun 14, 2020 at 22:22
  • \$\begingroup\$ Thanks—the graphics really show why it may be a better idea to shoot around f8. \$\endgroup\$
    – Skeleton Bow
    Commented Jun 14, 2020 at 22:25
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When you make photo of landscape you want to have (usually) something on the frontend. And have this thing in focus. So it's not to have only the mountain in focus but also some interesting object(s) close to you. This is probably one of the main reasons to use f8-f11.

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    \$\begingroup\$ Thank you—when I think about landscapes, I usually think of mountains and the like, so it didn't occur to me \$\endgroup\$
    – Skeleton Bow
    Commented Jun 14, 2020 at 20:05
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What aperture you should use really comes down to what you prioritise. I don't shoot a lot of landscape but for whatever reason I've found that I prefer the lower aperture at times as maybe I don't want everything in the picture to be super sharp, and that takes priority.

I think you should set your aperture to what gets you your desired feel rather than aim for maximum sharpness, as so long as your subject is in its desired focus it should be sharp enough.

If you want to prioritise sharpness that's fine, but maybe take a picture inbetween f8-f11 and take some pictures either side of those values and see what you prefer, and if the lack of sharpness in the apertures outside of 8-11 make a big enough difference.

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