This simple calculator will give you a rough idea on what kind of eyepiece length to look for for your scope according to advices from good fellows from SGL.

Please remember - this is only a rough proposal, and should not be considered as a "do it this way" guide.

I used same calculations to look for a eyepieces lengths using excel, and decided to bring them on web so I and anyone else could use them than needed.

All measurements are in mm.

Calculator use different formulas for fast scopes with F ratio 5 and below.