Was reading this post on SGL
Not sure if you can read it if you're not a member:
https://stargazerslounge.com/topic/309067-flymesh-bahtinov-mask/?tab=comments#comment-3381065
https://www.youtube.com/watch?v=IeUs7pFwMJw&feature=youtu.be
(https://stargazerslounge.com/uploads/monthly_2018_02/20180212_135104.thumb.jpg.0d362dbfc47147190a6337fffd364fbe.jpg)
(https://stargazerslounge.com/applications/core/interface/imageproxy/imageproxy.php?img=https://farm5.staticflickr.com/4767/26591464428_1ef695d7e2_b.jpg&key=d5891b3ef3d12b9cfa01da338f6a5ee2373196629467893ca53cdf44ea03c388)
Nice idea! It would certainly work.
The difference is that the diagonals are at 45 degrees so it's not as easy to judge when the vertical is exactly halfway between them. In other words, you won't get such accurate focusing with the flyscreen approach.
Mark