Allowing extensive "through fork" motion, the Tele Vue Long Schmidt-Cassegrain Adapter reduces the chance of obstruction between a Schmidt-Cassegrain's internals and a viewing accessory. On the front (where light would enter) is a standard female SCT threading such as you'll find upon many 5-10" Schmidt-Cassegrain telescopes, and on the rear (where light would leave) there is a standard 2" inner diameter barrel.
Tele Vue uses a brass clamping ring which fully encircles the device you're attaching, as opposed to other efforts which just use a simple set screw which can mar equipment or even lose tension.
Allows Schmidt-Cassegrain telescopes to use 2" eyepieces, diagonals, and other accessories
Brass clamping ring
Internally blackened