Many thanks to all of you who brought about this great tool! I posted some pictures of my version of the focus mask on the binoviewer section of this forum: Better focus method for individual eye diopter
Best regards, Rob Crockett
-------------------- Meade LX90 LNT 8" Schmidt-Cassegrain
Standard Wedge, LX90 fork, LX200 tripod
Alan Gee II telecompressor f/5.6
Baader short 1.5cm T-adapter/T-ring
Astronomik CLS-CCD clip filter
Self modified Canon XSi with Baader UV/IR filter.
Meade Model 277 60mm refractor with Orion SSAG
Losmandy V-dovetails for balance and guide scope.