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For example, a telescope with a 1000mm focal length and a 10mm eyepiece with a 50° AFOV results in 100x magnification. The TFOV is 50° / 100x = 0.5°, or about the size of the full Moon. A more accurate method uses the eyepiece's field stop, but the AFOV method is simpler and adequately accurate for most planning.
(arcseconds per pixel) to ensure you aren't "over-sampling" or "under-sampling" based on your local seeing conditions. Barlow/Reducer Factor: astro fov calculator 2021
The is the actual patch of sky you see through the eyepiece. Calculate Magnification ( ):
: A desktop planetarium that can simulate FOV with its "Oculars" plugin. It is highly accurate but requires careful input of sensor dimensions to avoid framing errors. Manual Calculation Formulas This public link is valid for 7 days
For astrophotographers, the concept is similar but uses a camera sensor instead of an eyepiece. The size of your camera's sensor (in mm) and the focal length of your telescope (in mm) determine the angular size of your captured image.
For optimal imaging, your resolution should match the atmospheric seeing conditions (typically 1 to 2 arcsec/px). Summary Checklist for 2026 Can’t copy the link right now
Telescopius gained popularity for its user-friendly interface that combines FOV calculation with target planning and visibility charts. How to Calculate FOV (The Formulas)