LIGHT-GATHERING AREA

The light-gathering area of a telescope is a quantitative measure of its ability to collect light for viewing. It can be defined in centimeters squared (cm²) or meters squared (m²), that is, in terms of the effective surface area of the objective lens or mirror as measured in a plane perpendicular to its axis. Sometimes it is expressed in inches squared (in²).
For a refracting telescope, given an objective radius of r, the light-gathering area A can be calculated according to this formula:
A = πr²
where  is approximately equal to 3.14159. If r is expressed in centimeters, then A is in centimeters squared; if r is in meters, then A is in meters squared.

For a reflecting telescope, given an objective radius of r, the light-gathering area A can be calculated according to this formula:
A = πr² - B
where B is the area obstructed by the secondary mirror assembly. If r is expressed in centimeters and B is expressed in centimeters squared, then A is in centimeters squared; if r is in meters and B is in meters squared, then A is in meters squared.

مواضيع ذات صلة

Mirror reflections

The sensation of color

Physiochemistry of color vision

The mechanism of color vision

The chromaticity diagram

Measuring the color sensation

Color depends on intensity

Aberration

The ω,k four-vector

Moving sources

Anomalous refraction

The intensity of reflected light