How's the best way to record two images coming through a single lens. One being a infrared and the other being visible. My plan was to use a beam splitter between the lens and the sensor to reflect the IR light into a second sensor while the visible light is transmitted to the other sensor. How would this mess with the focal point?
I'm just playing with the idea at the moment. Checking to see if it will work.
As a theoretical problem it's something that is very much solved as it's how 3CCD video cameras often work (as the 3 indicates they have separate R, G, and B sensors.) Replicating something similar with SLR's should be achievable though it may take some fettling to get right, it would definitely be a homebrew type project.
Splitting visible light from IR may introduce some challenges. You'd need a body modified to handle IR in addition to a standard SLR body. To maintain focus the sensors would also need to be slightly different distances from the split point so they're unlikely to line-up exactly even if the two bodies are the same model.
Then it's a case of syncing up the releases which can be done with a remote and that's it, you're done.
You'll be a lot better off if you can afford two separate lenses & sensors, as then each path (IR, vis) can be focussed separately. You may be able to adjust the back distance from the lens to each sensor, but it's never a good idea to put optics in the converging portion of the path (between lens and sensor). A tilted flat plate in the cone will cause coma in the image, for example.
