Focus (optics)
Videos
In geometrical optics, a focus, also called an image point, is a point where light rays originating from a point on an object converge. Although the focus is conceptually a point, physically the focus
A demonstration of camera focus on different distances, showing a bamboo rooftop
Text on a page that is partially in focus, but mostly not in varying degrees
Focal length
Videos
The focal length of an optical system is a measure of how strongly the system converges or diverges light; it has units of length, and for an idealized thin lens is equal to the distance between the l
Sketch of human eye showing rear focal length f′ and EFL
28 mm lens
50 mm lens
70 mm lens