f/8

f/8 is where most lenses resolve best. The aberrations that soften a wide stop have closed down, and diffraction has not yet arrived.

The result reads as plain truth. Everything is legible, nothing is chosen for the viewer, and the picture looks recorded rather than composed.

The sharp band covers most of a room on a wide or normal lens, so foreground, subject and background all hold.

Resolution peaks here on almost every lens ever made, which is why copy work, architecture and product photography live at this stop.

It costs light. f/8 passes a sixteenth of what f/2 does, so daylight or a lit set is usually the reason anybody is here.

Use it for street work, architecture, crowds and any frame that has to be readable rather than flattering.

Skip it for a close portrait. At f/8 the background comes forward and sits on the subject.

f/4 leaves the far background gently soft, so the shot keeps a sense of distance. f/8 hardens it and the picture goes flat.

f/11 pushes further into Deep Focus territory and starts to soften the whole frame with diffraction. The test is the far wall: legible is f/8, sharp and slightly mushy is f/11.

The old press photographer's rule was f/8 and be there. A camera preset to this stop was sharp from a few metres to the far side of the street, so the photographer only had to arrive and raise it.

The model adds background blur out of habit, because most of what it learned from is shot wide open. Ban shallow depth of field in the same line.

The other failure is a frame with no depth cue at all. Give the shot layers, so the sharpness has something to show.