Calculator
Field of View Calculator
The most common imaging disappointment is a target that does not fit the frame. This calculator works out the true field for an eyepiece or the angular field for a camera sensor, then compares it against the apparent size of well-known objects and tells you whether the framing works.
Result
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Measure
How to read these numbers
- True field ≈ apparent field ÷ magnification, valid up to roughly 60°; beyond that the approximation drifts and the field-stop method is more accurate.
- Camera field of view in degrees ≈ 2 × arctan(sensor dimension ÷ (2 × focal length)).
- A target filling more than about 70% of the frame usually crops the surrounding nebulosity that gives the object context.
These are planning figures computed from standard approximations, not measurements of your equipment. Atmospheric seeing, optical quality, collimation and sky brightness move the real numbers, sometimes a lot.