Why Bayer

[Jorge Díaz-Amador]

I didn't mean to use an optical flat as one would with a monochromatic light to read fringes when in contact with another optical surface. What I meant is that you can place a optical window on the lens seating surface of the camera mount and get a bounce back of both it and the film plane. It's an optical way to determine if the lens seat is paraellel to the film plane. It's a test we used to do with film cameras all the time. Also used it to square ground glasses to lens seats.

Chuck,

I thought the optical flat had to be in contact with the tested surface to see the fringes. We'd be talking about 52mm of air space (on in the case of RED, that plus the protection window).