Your digital camera’s aperture settings (f-stops) can make a world of difference, so choosing the right f-stop can be an important part of creating a perfect finished picture. You need different f-stops for different photographic situations:
Use an almost-wide-open f-stop to boost sharpness.
Most cameras and lenses are their sharpest when they’re closed down only one or two f-stops from wide open. This setting can also help you stop camera or subject motion, creating a clear action shot, like in this figure.
Adjust your depth of field by moving f-stops.
Changing your f-stops can stretch your depth of field usefully or trim it for creative effect. Stopping down or opening up an f-stop or two can produce dramatically different results, as shown in this figure.
Avoid too-small f-stops.
Using the smallest possible f-stop can cause defraction, and you lose any sharpness you think you gain in depth of field. In addition, small f-stops can accentuate the appearance of any tiny dust motes on your sensor (see this figure). These imperfections, at larger apertures, are fuzzy and virtually invisible.