Light gathering ability

The light-gathering capacity indicates the amount of light that enters an optical instrument in relation to the pupil of the eye .

With a single magnification, the light collecting capacity (L) corresponds to the ratio of the area of ​​the opening of the optical instrument (F _I ) to the area of ​​the pupil of the eye (F _A ).

${\displaystyle L={\frac {F_{\mathrm {I} }}{F_{\mathrm {A} }}}}$

The magnifying effect of an optical instrument (V) reduces the light gathering power by the factor of magnification.

${\displaystyle L={\frac {F_{\mathrm {I} }}{F_{\mathrm {A} }\cdot V}}}$

If there are objects in the beam path of the optical instrument, their area must be subtracted from the opening area. Furthermore, the quality of the optics used has an influence on the ability to collect light.

Individual evidence

1. ↑ Alexander Staidl: AstroScript. An introduction to astronomy. Part 1: A first overview, February 12, 2008, p. 55 ( Section: Light-gathering power of a telescope )