If you own a big SCT, and are still using a 1.25 diagonal, you are missing out on a whole new world. Using this adapter, which replaces the stock Celestron 1.25 one, allows you to mount a 2 diagonal directly through, giving a tremendous increase in light to the eyepiece. The quality of this piece, like virtually all Astro-Physics items, is superb. My CPC 1100 GPS XLT is like a completely different scope now. Highly recommended, high quality, and inexpensive considering what it gives you with respect to everything from planets to DSOs.