ATM autocollimating a camera-untested idea

["Nils Olof Carlin" <nilsolof.carlin@swipnet.se>]

Thinking about collimation today, a thought struck me - suppose you take a
small mirror and make a peephole in the middle like on an autocollimator,
but the mirror is rectangular to fit your cameraīs film path. Then you put
it there, and with your camera's back open you use the camera/mirror as a
regular autocollimator. This way, it is the actual film plane you set
perpendicular to the optical axis, with great accuracy (a thing I donīt
know a laser could do).

Did I reinvent somebody's (rectangular) wheel, or did I miss something
important? If not, this should be a very simple thing to make.

Nils Olof