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Question

Does f-stop matter when shooting subjects at a distance of infinity when there is a lot of light? What aperature should someone have when they are taking a picture of, say, a mountain in the distance and the foreground is already at the furthest focus distance? I tend to have a habit of opening my aperature as far as it will go so that I have more light and I can therefore use the fastest shutter and avoid camera shake. I’ve read that shooting with low f-stops gives poorer quality and that f8 is around ideal. Should I always instead be shooting at the highest f-stop allowable under my particular light conditions to get the highest quality shot? This is also considering that everything is at infinity and I’m not looking for a blurred depth of field effect.

I understand aperature in situations of low light or portraits when i want some of the photo blurred. I just dont know how to use it when everything is at infinity and there is enough light to shoot at most levels of aperature.

Answer

In general, 2-4 stops down from widest aperture will be the sweet spot for a lens. F/5.6 - 11.0 for an f/2.8 lens, f/8.0 to f/16 for an f/4.0, and so on. In general, the longer the lens the more you can stop it down and still be in the sweet spot, since f/stop is focal length divided by physical size of the aperture, and one of the limitations on sharpness comes from the “circle of confusion”, which becomes a problem at physically smaller apertures regardless of the f/stop they represent.

In plain English, f/22 on a 10mm lens is less than half a millimeter, and that’s a WAY tiny aperture, way too tiny to get maximum sharpness. So on the extreme WA lenses, which are typically f/4 lenses, f/8 is about as much as you want to stop down to balance DOF with sharpness issues. On the other hand, a 200mm lens is likely to be close to optimum all the way up to f/16, even if the maximum aperture is f/2.8.

There are other considerations, of course, with lens being designed to generate maximum optical performance at a given f/stop (they can’t be perfect all the way through, it’s impossible pretty much especially with zooms) but good modern lenses have very nice optical performance pretty much throughout their range, with CoC becoming a real limiting factor especially on WA lenses.

It took me a while to learn this about my 10-22mm, shamefully. I used to use it at f/22 all the time, for maximum DOF, but the DOF is outstanding even wide open, and the CoC really comes into play at the smaller apertures.