An off-axis guider (OAG) uses a small prism in front of the imaging camera to pick off a star at the edge of the telescope's field and send it to a guide camera, so guiding runs through the same optics as the image and the flexure between a separate guide scope and the main telescope is avoided. The main choice is size and fit: compact units such as the ZWO OAG, Player One FHD-OAG MINI and QHYCCD OAG-S suit smaller sensors, while the ZWO OAG-L, ZWO M68 OAG and Player One FHD-OAG MAX are built for larger sensors and wider-threaded imaging trains, and back focus should be checked against your camera and corrector. If you would rather guide with a separate scope, see Guidescopes.
