SEATTLE—Primes are single focal length lenses, which can be designed with a relatively few optical elements and thus are capable of transmitting a lot of light to the film or digital camera sensor.

Photography is full of fancy terms and complicated science, but we are here to explain it all to you in simpler terms. Today we are focusing on focal length. This term gets thrown around often, ...

The F-number of a photographic lens is a measure of its light-gathering ability, and is expressed as its aperture diameter divided by its focal length. Lenses with low F-numbers are prized by ...