Celestron NexStar 127SLT Maksutov-Cassegrain

The Celestron NexStar 127SLT is a 127 mm Maksutov-Cassegrain on a computerised altazimuth mount, listed at £599 and third in our guide to telescopes. It is also one of only two listings in that guide whose numbers survive a calculator. A 127 mm aperture against a 1,500 mm focal length gives f/11.8, and the listed Dawes limit of 0.91 arc sec is what 127 mm of aperture works out at. The listing also gives a 3.53 mm exit pupil, which on a 127 mm aperture means roughly 36x.

That is the contrast with the rest of the guide. Three other listings there pair a 130 mm aperture with 325 mm or 260 mm of focal length — f/2.5 and f/2 — and a 102 mm with 204 mm, also f/2. Here the arithmetic holds. Two things on this sheet still do not line up neatly. The "Eyepiece Lens Description" field says "Maksutov", which is the optical design rather than an eyepiece, and no eyepiece focal length is given anywhere. The listed dimensions of 40 x 19 x 11 cm match the 381 mm optical tube rather than the assembled telescope on its tripod, so the 8.21 kg item weight is the only figure covering the whole kit. Everything below is taken from the Amazon listing, not from any test of our own.