The #777 Off Axis Guider provides a means, during long exposure astrophotography, for the photographer to monitor the tracking of the telescope, to assure that the telescope remains precisely positioned on the object being photographed. Like the T Adapter, the Guider couples the camera body to the telescope but it also causes a small amount of the guidestar's incoming light to be diverted at a right angle, where the star's position can be examined for tracking errors with an illuminated reticle eyepiece; position corrections can then be effected using the telescope's hand controller or drive corrector.