Light-gathering power
Compare the apertures of two instruments and the human pupil.
How the calculation works
The comparison uses aperture area and ignores losses, obstruction and coating transmission.
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.