Control depth of field
Shutter speed is, of course, the crucial camera setting to get right when targeting sharp shots, but the aperture plays a significant role as well. The choice of aperture has a big influence on the depth of field – or the depth of sharpness through the image. Small apertures, such as f/16 and f/22, increase the depth of field while large apertures – f/1.4, f/2.8, f/4 and so on – decrease it. It might seem wise to reach for small apertures to boost the sharpness, but there are two big drawbacks. First, you’ll need to use a slower shutter speed or higher ISO to expose the scene properly, and second, the smaller the aperture, the more obvious the effects of diffraction become. Diffraction is an optical phenomenon where light rays entering the lens are bent out of shape by the edges of the aperture blades. The smaller the hole, the greater proportion of light rays strike the aperture blades, and the more fuzzy details and edges in a picture appear. Sticking with apertures in the middle of the range tends to give the best balance of depth of field and optical sharpness.
Don’t dismiss large apertures either. Having a shallow depth of field, with a sharply focused subject sandwiched between a blurred foreground and background, can actually enhance the impression of sharpness where it counts.
Andy used a specialist tilt-and-shift lens to give him precise control over the depth of field and plane of focus in this image of sailor Giles Scott. Though most of the frame appears defocused, Giles’s face is pin-sharp, drawing your attention.