This adapter threads onto the standard 8", 9.25" SCT back and accepts 2 inch accessories - eyepieces, etc. Astro-Physics item ADASCT. Brass locking ring and 2 thumbscrews. The adapter is 2.06" in length. I have used this with a C11 and an SBIG camera with no difficulty. Sold the C11. The list price is $40.00.