[Worker 11811]

I have filed the edges of my carriers to an angle around 45 degrees and painted them black to stop this very thing.

The exact same thing is done in cinema projectors. You bevel the edge of your aperture plate at about 45º.
Cinema projector aperture plates are hard brass so, as long as they are smooth, you don't need to worry about stray reflections. Beveling is done, mainly, to make the edges of the image appear cleaner.