This one is a bit difficult for me to explain as my understanding of slit/interference cameras is pretty dim. As far as I know, with a true slit camera, the light source should be a single stream of photons. The “lens” is a row of vertical slits. When the stream of photons passes through the slits, interference patterns are created on the film, thus proving that light can act as a wave, because interference patterns are distinctive to waves.
Jorge Otero sent me some interesting info on some slit cameras that he made. You can find it here.
I had the idea to make a pseudo-slit lens for the Cámara Galletita Lumen out of aluminum foil. I knew it probably wouldn’t demonstrate interference patterns as I was just going to place it out in the sun in the garden, which is very far from being a single stream of photons.
I set it outside for a 4 hour exposure (me just guessing what would make for a good exposure) and I got something. I’m not sure what, but it’s something! I plan to proceed with these experiments in the near future, I think this one was slightly overexposed. I’ll try a shorter exposure next time.