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 cause vignetting compared to adapters for ASI cameras in general.