Plate scale

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 F is measured in mm, the plate scale in radians per mm is given by p = θ / s = 1 / F

since s = F θ

Plate scale is usually expressed in arc-seconds per mm

p = 206265 / F , where F is in mm.

Plate scale on JWST FGS/NIRISS

The plate scale of the James Webb Space Telescope component Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph is about 0.065 arcsec/pixel. It uses a 2048 x 2048 pixel array with a pixel size of 18 microns a side with a field of view of 2.2' x 2.2'

See also

• Photographic plate