The Variable Projection Camera Adapter allows for a range of effective focal ratios during eyepiece-projection photography. For telescopes with 1.25” focuser. Inserts into any 1.25” eyepiece holder and a 1.25” eyepiece is then typically inserted into the VPCA, usually in the 15mm to 32mm focal length range. The machined sliding-cell assembly can be fixed at any position along its length and is held in position via thumbscrew. The resulting effective focal ratio is then determined by the sliding adjustment and eyepiece used. For film based SLR cameras a T-Mount is required, ordered separately for your 35mm camera brand. Compatible with all Meade SCT and ACF models. Can be used for prime focus photography without eyepiece.