Plate scale

File:Plate Scale.gif

The plate scale of a telescope connects the angular separation of an object with the linear separation of its image at the focal plane.

If focal length $f$ is measured in mm, the plate scale in radians per mm is given by angular separation θ and the linear separation of the image at the focal plane s, or by simply the focal length f:

:$p\; =\backslash frac\{\backslash theta\}\{s\}\; =\backslash frac\{1\}\{f\}\backslash \; ,$

since

:$s\; =f\; \backslash theta\backslash \; .$

Plate scale is usually expressed in arcseconds per mm:

:$p\; \backslash approx\backslash frac\{206265\}\{f\},$

where f is in mm,{{cite book |title= An Introduction to Modern Astrophysics |edition= 1st |last=Carroll |first=Bradley |author2=Ostlie, Dale |page= 163 }}

or expressed in arcseconds per pixel after further division through the pixel scale.