Autoguiding a Telescope for Deep Sky Astrophotography (Basic Setup)
Guide Scopes for Astrophotography | A Complete Guide
125 mm Guide Rings - Stellarvue
Amazon.com : Astromania 10x60 Finder Scope + Guide Scope 45° Angled with Illuminated Reticle Eyepiece - Used as a high-end Finderscope, Guide Telescope, Spotting Scope, or Small Travel Companion Astro-Telescope : Electronics