This is the distance that a lens takes to focus light coming from infinity.
About 45-55mm = “Standard Lens”
12 mm – 35 mm = “Wide-angle”
100 – 500 mm = “Telephoto”
These are calculated for 35 mm film. Smaller
digital sensors generally have a 1.5 times multiplication factor. (i.e. a 35 mm wide-angle lens acts as if it is a standard
lens)
A P E R T U R E
The reciprocal of focal length (1/focal length) can be used to measure “aperture”
of a lens.
Small apertures let less light reach the film or digital sensors, but give greater depth of
field (i.e. more of the photograph is sharply in focus, from close to the camera to the far distance)
Wide apertures let more light reach the film or sensor, but give a shallower depth of field.
