Scope  Calculator This interactive telescope calculator is designed to give you answers to commonly asked questions about an instrument's performance when changing eyepieces and accessories.

Scope aperture Scope focal ratio Eyepiece focal length Eyepiece apparent field Barlow lens Focal reducer   inch mm f/ mm 30 degrees 35 degrees 40 degrees 42 degrees 45 degrees 50 degrees 52 degrees 55 degrees 57 degrees 60 degrees 65 degrees 66 degrees 70 degrees 75 degrees 80 degrees 82 degrees 90 degrees 100 degrees None 1.5 x 2.0 x 2.5 x 2.8 x 3.0 x 3.5 x 4.0 x 4.5 x 5.0 x None 0.2 x 0.3 x 0.4 x 0.5 x 0.6 x 0.7 x 0.8 x

Here is an analysis of your telescope's performance using the parameters selected above: .........