True field of view — approximation
Estimate sky coverage from apparent field and magnification.
Warning — the Sun
Do not use this result for solar viewing without a special-purpose filter secured over the front of the optics.
How the calculation works
AFOV divided by magnification is an approximation affected by eyepiece distortion.
Example use
Example values are prefilled. Replace them with specifications from your equipment manual, then compare the result with another eyepiece or optical factor.
Limitations
The result is a geometric calculation or a rule-of-thumb estimate. It does not include every optical loss, manufacturing tolerance, atmospheric condition or individual eyesight difference.
FAQ
Does this replace manufacturer data?
No. Manufacturer specifications and the instrument manual take priority.
Can I save the result?
You can copy or print it; save equipment specifications in the local catalogue.