Attach your camera onto the Vixen Optics Dovetail Slide Bar PGA using one of the three 1/4"-20 bolts, then mount the bar on a compatible 44mm Vixen-style saddle. This bar was primarily designed for use with the Advanced Polaris Photo Guider and AP Star Tracker, but will fit other mounts and saddles. An elongated hole in the center of the bar allows the camera to be balanced around the optional polar alignment scope.