Photography的几个基本概念

Angle of View

和Field of View应该是同一个概念

35 mm equivalent focal length

Crop factor

The terms crop factor and focal length multiplier were coined in recent years in an attempt to help 35 mm film format

SLR photographers understand how their existing ranges of lenses would perform on newly introduced
DSLR cameras which had sensors smaller than the 35 mm film format, but often utilized existing 35 mm film format SLR lens mounts.

Ultra-wide lens designs become merely wide;
wide-angle lenses become 'normal'.

Three basic photographic lens types (classified by relative focal length)

Normal Lens
Wide-angle_lens
Long-focus lens

Long-focus lens

Long-focus lenses are best known for making distant objects appear
magnified. This effect is similar to moving closer to the object, but is not the same, since

perspective is a function solely of viewing location.
Two images taken from the same location, one with a
wide angle lens and the other with a long-focus lens, will show identical perspective, in that near and far objects appear the same relative size to each other.
Long lenses also make it easier to blur the background more, even when the
depth of field is the same (???)

Four Thirds system