Here is a unique adapter from Blue Fireball that effectively does the work of two adapters in one. In many telescope configurations, the focal plane is extended (pushed out) by the use of some accessories. Reaching focus with a camera for imaging applications then requires an extension tube. The typical solution is to use an extension tube followed by the prime focus adapter. With this adapter, you get a 2" prime focus adapter and a 40mm extension tube in one piece, thus allowing you to overcome additional out-focus travel requirements.
The 2" barrel slides into 2" focusers in telescopes and diagonals. The male T-thread at the other end allows you to attach a camera (with an appropriate T-ring, sold separately) for prime focus photography. The 2" barrel is threaded to accept standard 2" filters.
Total length = 80mm, Extension provided is 40mm (1.57"), T2 thread outside. Weight = 4.1oz.