Input

Fill in the following details then click "Calculate".

Telescope focal length mm  
Telescope aperture mm You can fill in aperture or f-ratio. You don't need to fill in both.
Telescope focal ratio (e.g. f-?)

Eye­piece Name or Number (optional) Focal Length (mm) Apparent Field of View (deg)
Barlow Name or Number (optional) Mag­ni­fi­ca­tion Factor (x)