Focal length is used to determine your lens's angle ... as it's particularly suitable for portraits and close-up photography. The best macro lenses are usually short telephoto focal lengths ...

A macro lens can give you impressive close-ups. Photo: Erin Lodi A 70mm focal length is also pleasing for portraiture with a full-frame DSLR, as is the 105mm equivalent on a crop-sensor camera.

The F-number of a photographic lens is a measure of its light-gathering ability, and is expressed as its aperture diameter ...