This is a part for attaching Canon lenses to M54 connections, such as those found on ZWO full-frame cooled CMOS cameras and the 2600mc DUO. It allows for the installation of 2-inch filters internally, but because the orientation is reversed, you'll need to flip the filter or use a filter that doesn't have a specific front or back. The narrowest point in the light path is the filter mounting section, so it's less likely to vignette compared to adapters for ASI cameras in general.