an astronomical data collection method employing a novel optical reticle projector . prior art ground - based optical systems for astronomical data collection typically comprise a main telescope , and a guide telescope comprising an internal reticle . the guide telescope presumably corrects nominal tracking errors , but may itself , by way of the internal reticle , develop supererogatory errors due to differential flexure . the method of the present invention addresses the problem due to differential flexure , and solves it , by minimizing a source of the supererogatory errors , while recreating an internal reticle function in the novel optical reticle projector .