Originally Posted by
Pere Casals
Your wall test is correct, if you replace the wall with a GG, as Michael said, it should project just the same. I'd do again the wall test to be sure that it's working like before unscrewing the rear, then measure the flange to the wall distance, and use same distance for the flande to GG.
When doing the wall test do not focus the window itself, but subjects that at very long distance and that are seen thought the window, be careful if you use sun, it's a bright reference but you can burn something, even one eye...
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