Orion 5521 Deluxe Off-Axis Guider for Astrophotography Orion's Deluxe Off-Axis Guider lets you image and guide simultaneously through the same astrophotography telescope, eliminating the need for a separate guide scope Eliminates tracking problems caused by using a separate guide scope such as differential flexure and mirror shift, and also helps reduce imaging setup time and overall weight Compatible with astrophotography autoguiders that feature T-threads or a 1.25" nosepiece, as well as 1.25" illuminated reticle eyepieces Attaches to any 2" telescope focuser via the included 2" nosepiece, or onto any T-thread equipped rear-cell. Includes T-extensions of three different lengths (7mm, 17mm, and 30mm) to accommodate different camera/guider combinations Features prism tilt adjustment and more than 100 degrees of radial adjustment for easy guide star location. Requires a minimum of 59mm inward focus travel