Fit My Telescope guides
Practical guides to measuring, sizing and choosing the right part, from the same sourced data behind the fitment tool.
Telescope eyepiece barrel sizes: 1.25 inch and 2 inchThe two standard eyepiece barrel diameters, which telescopes take which, and how adapters let a 1.25 inch eyepiece work in a 2 inch focuser.Telescope focal length and magnification explainedHow magnification is set by the telescope's focal length divided by the eyepiece focal length, and the useful upper limit set by aperture.Telescope mount types: alt-azimuth, equatorial and DobsonianThe main telescope mount families, how alt-azimuth, equatorial and Dobsonian mounts differ, and which suits visual and imaging use.Exit pupil and focal ratio: matching eyepieces to your telescopeWhat exit pupil is, how it is calculated from aperture and magnification, and why focal ratio guides which eyepieces suit your telescope.How to work out your telescope's specsFind your telescope's aperture, focal length and focal ratio from the model markings so you can choose eyepieces and accessories that fit.Vixen versus Losmandy dovetail: telescope mounting barsThe two dovetail standards that attach a telescope to its mount, their widths, and which mounts and tubes use which.Telescope camera thread standards: T2, M42 and SCTThe threads that connect cameras and accessories to a telescope, from the T2 ring to the SCT rear-cell thread, and how they combine.Choosing a Barlow lens for your telescopeWhat a Barlow lens does, how a 2x or 3x multiplies your eyepieces, and how it interacts with the useful magnification limit.