I have the ground glass attachment for my Koni-Omega, and as I'd just gotten my K-O back from the shop, I wanted to give it a try. One thing I want to check is whether my rangefinder is accurate--some shots on the first rolls I put through it suggest it is not. I've taken the back off and inserted the ground glass in its place, but I can't figure out how to get the shutter to open with no back. (And, no, I am not even certain I have the ground glass inserted correctly.) Is there a way to trick the locking mechanism?