"Be there at f/8" more to it? (Hardware question)

[timmyquest]

I know that at a certain point an image will being to get less sharp in regards to how stopped down the lens is.

I recently read "this is why many point and shoots are limited to f/8" which reminded me of the saying "Be there at f/8".

It got me thinking, is F/8 the sweet spot? Does the image degrade after F/8-ish?

I always thought it was more around F/22

And...GO!

[aam1234]

I'm by no means an expert in the matter, heck I'm not an expert in anything about photography, but from what I've read, the sweet spot is 2-3 stops from the biggest (or widest) aperture. Btw, and according to what I've heard/read, both extreme apertures are not good.

Hope that helps

side note: that's one of the reasons I don't care about speed (as I mentioned in another thread)

[Jon]

The "f/8 and be there . . . " is more an early press photographer's prescription for getting the shot. They weren't about to lose the moment while fussing with exposure settings. f/8 was a pretty safe pre-set for the Speed Graphics and so forth for capturing a picture that wouldn't be unusably under- or over-exposed. On the larger formats, diffraction didn't come into play like it does in today's smaller formats, so f/16 or f/22 would still be pretty good (especially with the lower-quality glass of the time).

Now, you can start seeing diffraction effects come in at larger apertures, so in terms of lens quality, f/8 is a pretty safe number (maybe not on p/s cameras - if they're really cheap, they may not have a sweet spot) for taking maximum advantage of the lens quality you do have.

[hmhm]

The aperture that yields the highest resolution is dependent on the lens design. Most lenses are a little soft wide open due to aberrations, and sharpen up as you stop down. But there's no "law" or "rule", here, just rules of thumb.

At the other extreme, you start to lose resolution due to diffraction at very small apertures. Somewhere in the middle is an aperture that yields maximum resolution for the in-focus subject. You can expect this to be somewhere in the neighborhood of f/8 - f/16 for 35mm and 1.6x DSLRs. Note that things get more complicated for subjects away from the focus point, as the increased depth of field of smaller apertures may outweigh the softening effects of diffraction (i.e. yielding "less blurry").

There's nothing magical about f/8 . In particular, you need to interpret an aperture in the context of the format (size of film or sensor). For 35mm (or close to it, like 1.6x DSLRs), f/8 is a "middle" aperture, with moderate depth of field and minimal diffraction. For large format (e.g. 8"x10"), f/8 would be considered "fast", with very narrow depth of field. On a teensy-sensor point 'n' shoot camera, f/8 is very narrow, and provides extremely broad depth of field, and visible diffraction.

With respect to diffraction and depth of field, f/8 on a point 'n' shoot is comparable to f/22 on a 1.6x DSLR. So, in short, point 'n' shoot cameras don't stop down past f/8 for the same reason that most 35mm lenses don't stop down past f/22, because that's about where diffraction starts to kick in, and it provides "enough" depth of field for most typical needs.
-harry

[rick barclay]

Am I wrong to say it only works if it's the right lens in the right light?

I've been doing a lot of shooting with a 2x extender recently, and I've been trying to keep the aperture near f/20, which isn't all that easy to do with a
100-400mm lens. On a cloudy day, I find myself shooting as wide open as possble to get decent exposure even without the extender. Along with
this, my iso is set around 1000 and my temperture setting is 10000.