I'm looking for a low-cost way to play with images projected from my pico projector. I want to orient the projector horizontally, but project the image downward onto the table. I was going to purchase two lenses and a mirror and test the results against my rough calculations, but then I saw that vendors on ebay sell self-contained units with a 90 degree prism and optics.
I assume it makes the most sense to purchase a single unit with the optics and prism inside, but are there any downsides? What specs should I look out for with these products? I've only had limited experience with machine vision lenses, where my imager is looking straight down through the optics, and working distance and field of view are the main specifications that I have to check.