This is a premium 1.25" star diagonal mated to an F/5 focal reducer that Celestron made in the 80s and sold for$265. Cutting your focal ratio in half gives you 4!X brighter images and drastically cuts astrophoto exposure times while giving you double the FOV observing.Celestron's literature says it gives wider views than using 2" oculars and "makes a spectacular combination for deep sky observing of nebulae" used with a nebula filter. Rare and collectible out of production item. Excellent cond. Screws directly onto std. SCT rear cell threads.
There is a lot of confusion about this item so let me know and I will send out a PDF description from Celestron catalog.