# Telescopes

(Difference between revisions)
Jump to: navigation, search
Ana (Talk | contribs)
(Created page with '== Basic geometry == Plate scale of a telescope is 1 radian in the sky (measured in arcsec) "seen" in the focal plane of the telescope at the focal length (measured in millimete…')

## Basic geometry

Plate scale of a telescope is 1 radian in the sky (measured in arcsec) "seen" in the focal plane of the telescope at the focal length (measured in millimeters). Focal length of the telescope is equal to the product of the F-number (F#) and the diameter of the telescope's primary mirror D[mm].

``` plate_scale =  1 radian [arcsec] / (F#*D[mm])  = 1 radian [arcsec] / f[mm] = 206265 ["] / f [m] * 10^(-3)
```

e.g. Milanković telescope has a focal length of 11.2 m, aperture of 1.4 m and F#=8: plate_scale = 206265 / 11200 = 18.42 ["/mm].

Pixel scale is the size of the pixel 'in the sky':

``` pixel_scale = plate_scale ["/mm] * pixel_size [mm/pix]
```

e.g. CCD camera U42 used with the telescope has 2048 x 2048 pixels of 13.5 μm each. So, 1 pixel = 13.5 * 10^(-3) mm, i.e. 1 mm = 1/13.5 * 10^3 1/pix: pixel_scale = 18.42 ["] * 13.5 * 10^(-3) = 0.249 "/pix.

``` FOV = (#pixels x pixel_scale) x (#pixels x pixel_scale) = (2048 x 0".249) x (2048 x 0".249) = 509".3 x 509".3 = 8'.5 x 8'.5
```