Posted a while back but to no avail. I've since done some tinkering but need a little bit of help perfecting the math. I've constructed an experimental version of the above set up with success. Moving the plano-concave element away from the plano convex element brings the focal point towards the sensor. Moving the concave element back towards the convex element pushes the focal point further away. What I'm trying to figure out is what power or focal length lenses I need to construct this. I want minimal movement (around 5-10mm) and to be able to achieve infinity (afocal). Any advice is much appreciated!