■ Focus bracketing means the camera takes a sequence of shots, automatically adjusting focus between each frame. How many shots and how much focus is adjusted depends on what you have set; bracketing can also be done manually. Ideally, you need a static subject and camera, but handheld brackets of very slightly moving subjects are possible. The shots are focus-stacked on the computer, either in specialist software (such as Helicon or Zerene) or using Photoshop or Affinity Photo. A few cameras have focus stacking built-in; the best implementation of this is in OM System cameras, where images are merged to give a jpeg, and the original shots are retained for stacking in software. Focus stacking is useful when you want more depth of field than is possible with the lens and aperture in use, and it is especially useful for macro, where the depth of field is very narrow, even with small apertures. It means you get a fully sharp subject set against the background blur of a wider aperture.
Will Cheung