Plate scale

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The plate scale p of a telescope connects the angular separation θ of an object with the linear separation s 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 p=θ / s = 1 / F, since s=Fθ.

Plate scale is usually expressed in arc-seconds per mm p=206265 / F, where F is in mm,[1] or expressed in arc-seconds per pixel after further division through the pixel scale.

Plate scale on JWST FGS/NIRISS[edit]

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.[2] 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' [3]

See also[edit]


  1. ^ Carroll, Bradley; Ostlie, Dale. An Introduction to Modern Astrophysics (1st ed.). p. 163. 
  2. ^ [1]
  3. ^ [2]