The plate scale of a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...

connects the

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in par ...

of an object with the linear separation of its image at the

focal plane In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the '' focal points'', the principal points, and the nodal points. For ''ideal'' ...

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 =\frac =\frac\ ,

since :

s =f \theta\ .

Plate scale is usually expressed in arc-seconds per mm: :

p \approx\frac,

where ''f'' is in mm, or expressed in arc-seconds per pixel after further division through the pixel scale.

Plate scale on JWST FGS/NIRISS

The plate scale of the

James Webb Space Telescope The James Webb Space Telescope (JWST) is a space telescope which conducts infrared astronomy. As the largest optical telescope in space, its high resolution and sensitivity allow it to view objects too old, distant, or faint for the Hubble Sp ...

component

Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph (FGS-NIRISS) is an instrument on the James Webb Space Telescope (JWST) that combines a Fine Guidance Sensor and a science instrument, a near-infrared imager and a spectrogra ...

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 The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Human ...

of 2.2' x 2.2' http://www.stsci.edu/jwst/instruments/niriss/instrumentdesign

Notes

Astrophotography {{astronomy-stub

Plate scale on JWST FGS/NIRISS

See also

Notes