Quote Originally Posted by holmburgers View Post
...I think that these Curtis and Devin one-shots used half-silvered mirrors, but I know you're set on the beam splitter idea and that indeed could be a great route to take....
That's all a beam splitter is, a half silvered mirror. Take a look at the Edmund's Scientific stuff.

Quote Originally Posted by holmburgers View Post
... I've just read numerous accounts in old books about how tight the tolerances need to be to ensure that the 3 negatives are in the identical plane of focus.
That's why I think building to tolerance is a tough plan. You have to build with the plan to shim as required, and do it empirically.

I'm sure someone here knows how, but truth be told I'm certain I cannot calculate how the wavefront of the image changes with some parts going through one sheet of glass, and other parts going through two sheets. I know that affects the physical distance because of the transmission medium differences in the paths. But not in any way that I can predict.

So, you build adjustment into the device, and you tweak!