Schmidt-Cassegrain telescopes focus by sliding the primary mirror foward and backward over the central baffle tube. This design gives them a problem known as mirror flop. As the telescope moves across the sky tracking an object, the mirror can wobble on the central baffle. This is particularly true as it crosses the meridian when the primary mirror goes from leaning east to leaning west. It is also particularly true for a C14, which has a very heavy primary mirror that is prone to flop. Mirror flop can affect the telescope’s collimation, resulting in coma. The other big issue for astrophotography is that it changes the illumination pattern on the CCD chip, resulting in flat field errors during image calibration. There are a variety of remedies, such as imaging mostly to the east of the meridian and taking flats for different positions in the sky. Another is the use of Flop Stoppers. They are two special bolts on long plungers that can be screwed into the rear of the primary mirror in 2 places through special locking collars which can be attached to the rear cell of the telescope. The plungers slide in and out through the collars during focusing, but once focus is achieved, they can be locked in position with set screws. The focusing mechanism itself, on the opposite side, then acts as a third point of triangular fixation. They are beautifully machined by Thomas Esmerelda in Hawaii. While they don’t completely prevent mirror flop, they help greatly.