"The Alstar 1.25" Variable Universal Camera Adapters allow attachment of a camera body to reflector and refractor telescopes for either prime-focus or telescope eyepiece-projection photography. The adapter's 1.25" nosepiece slides into the telescope's eyepiece holder just like an eyepiece. This Variable Universal Camera Adapter is composed of two detachable parts: a prime-focus adapter (or ""T-adapter"") for prime-focus photography, and a fixed-length or variable extension tube for eyepiece-projection photography. A thumbscrew in the extension tube holds the telescope eyepiece in place. This combination of prime-focus and eyepiece-projection camera adapter has a sliding barrel design that allows variable projection distances. This allows for slight changes in magnification without swapping telescope eyepieces when performing eyepiece-projection photography. Fits reflector and refractor telescopes with 1.25"" eyepiece holders. The Variable Projection Camera Adapter allows for a continuous range of projection magnifications during eyepiece-projection photography for telescopes with a 1.25"" focuser.The machined sliding-cell assembly can be fixed at any position along its length and is held in position via a thumbscrew. The resulting effective focal ratio is then determined by the sliding adjustment and eyepiece used. A T-ring specific to your D/SLR camera is required to connect your camera to this adapter (not included). "