[xa-coupe (Jeff)]

I've finally decided to work on setting backfocus on my setup. It's seems straight forward until you add something like a filter drawer.


A WO GT81 with a reducer needs a 55mm backfocus ( according to the WO site) but a canon DSLR has a 44mm flange to sensor distance, and a filter drawer (ZWO) adds 31.5 mm ... making 75.5mm or 20.5mm more than I need.


2 questions;


1: am I adding this all up correctly?
2: If I am, other than removing the drawer and adding the filter 'permanently' is there anything I can do?


TIA.