ZWO T2/M42-T2/M42 21mm Extender - ZWO-T2-EXT-21

This extender is designed to help you to reach 55mm or any other back focus distance.

Attached to the ASI071MC-C:

In this example the aim is to reach 55mm with an OAG: attach the 21mm extender to ASI071 to reach 55mm back focus distance:17.5mm+21mm+16.5mm=55mm