Interesting question came up the other day - why do we go for f11 as the "preferred" aperture on our lens?
Well, it is a bit of a "add salt to taste" thing. Different photographers will have different favourite f-stops, particularly as the wider (lower number) you go, the more the background is pushed out of focus.
But your depth of field at lower apertures is incredibly tight, so it is about getting reasonable sharpness across a reasonable depth of field.
F11 on 80mm lens at 4 feet, focus range is about 5 inches.
F1.6 on 80mm lens at 4 feet, focus range is about 1 inch - that's pretty shallow.
In location work, the lower f stops are great for throwing the background out of focus, in studio that's usually less of a requirement because you are on plain backdrops.
On the other hand, if you're shooting the large family formals at a wedding, you want to go the other way f22 or beyond, to give you the greatest depth of field to make sure everyone is sharp from front to back of the crowd (f22, 50mm lens, 10 yards gives about 20 feet Depth of Field).
Max lens sharpness tends to be middle of the aperture range of a lens, so that usually means f11
If you put your camera in auto mode and wander round picking out bright to shady spots in the viewfinder you'll see your camera is probably always adjusting shutter speed to get around f11/f16 - the manufacturer sees that as the sweet spot too.
It is a kind of default setting for studio lighting too. For instance at half power my Bowens strobes give me an f11 at typical working distance.
But, when push comes to shove, your required depth of field is your principal aesthetic control, with shutter speed quite secondary, so adjust your f-stop to get the depth of field you want.
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