ToupTek GS PAPO Guide Scope

ToupTek’s GS guide scopes use a PAPO design: a three-element apochromat with an ED element and a built-in field flattener (the GS-100 uses four elements). Stars stay round across a 1″ corrected field, which covers any guide camera and sensors up to the size of the IMX533. That gives the guiding software more usable stars and a steadier result.

Choosing a focal length

ToupTek suggest a guide scope of about a third to a half of the main telescope’s focal length: a GS-250 for a 750 mm telescope, for example. With a 2.9 µm guide camera such as the GPM662C, the GS-250 samples at 2.4″ per pixel. The GS-100 suits camera lenses and small refractors.

AC or AR

Both versions have the same optics. AC versions have a Crayford-type focuser with no rack, which is light and fine to adjust: the choice for guiding only. AR versions have a geared rack and pinion focuser that carries more weight and takes ToupTek’s Astro Automatic Focuser, so choose AR if you’ll also image or visually observe through it.

Fitting

The camera end takes 1.25″ guide cameras and has an M42 × 0.75 thread, with focus 42–77 mm behind the focuser. An M48 extension tube with a removable short section lets you use an eyepiece or diagonal for visual use. The mounting ring has M5 holes, and the base has M6 holes and a 3/8″ thread.