I have to admit I have abandoned the project. After the experiments I've done, I feel it's impossible to put the eye-accommodation sensor into the eyepiece. The problem of lens flare (reflections), coupled with lowness of red-eye backscatter and ridiculous size constraints imposed by space available in the eyepiece, all that makes me feel the project is hopeless. I may make another go at it in the autumn, but I'm not sure.