* Astronomy

Apparent Field and True Field of view

Telescope eyepieces determine the true field of view you see in the sky.

To calculate the true field of view (in degrees °, divide the telescope eyepiece field stop diameter by the telescope's focal length and multiply the result by 57.3 (the quotient of 180 divided by Pi).

True field of view = eyepiece field stop diameter ÷ telescope focal length x 57.3

Unfortunately this relies on you knowing the eyepiece field stop diameter size;  information which most manufactures don't publish.

Online Telescope Field Of View And Power Calculator

This calculator is designed to give the true field of view and magnification of a telescope.
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