For 40+ years now, I've always held thin gel filters against the front of the lens whenever I needed a filter (don't actually use 'em all that often.) I have a need to use a glass filter because my hands will be working a computer. I've seen other photographers using filters on the front of the lens, but is there any considerations or reasons why I couldn't screw one onto the rear element? Assuming, of course, that threads are available. Seems like it would be a good place to have a filter; eliminate reflections, light flare, etc. Would vignetting be an issue? Would the image quality be degraded?

Thank you.