The camera

A camera uses a single lens (or a group of lenses treated as one equivalent lens) that forms a real, inverted and reduced image on the sensor (CCD/CMOS, once film). Unlike the eye, here the focal length $f$ is fixed and the distance $q$ between lens and sensor is varied to focus on objects at different distances: this is the focusing of a modern lens.

The aperture (the effective diameter of the entrance pupil) controls the amount of light: the inverse of the ratio $f/D$ is the $f$-number printed on the lens. An $f/2$ lets in $4\times$ more light than an $f/4$, because the area is proportional to $D^2$.

Note

The depth of field (the range of distances in focus) increases as the diaphragm is closed, that is by reducing $D$: large $f$-numbers give everything in focus; small $f$-numbers give an artistic blurred background (bokeh).

Collegamenti

Argomenti: Ottica Concetti: Lenti e specchi

Esercizi collegati: Problema — Raggi per oggetto oltre 2f (lente) · Problema — Raggi per specchio concavo con p minore di f · Esercizio svolto — Specchio concavo