This M42 to C or CS adapter allows you to add a C or CS lens to compatible ASI cameras, including the ZWO 2.8 - 12mm f/1.4 lens or the 150Âș fisheye. The adapter is 7mm thick and has female CS mount threads along the inside diameter and male T threads on the outside.  The back focus of a C lens is 17.5 mm, while the back focus a CS lens is 12.5mm.
Lens shown is sold separately.