Nice 1
- Well worth your work in modifying the lens.
On the subject of your DIY Hyperstar,
it wouldn't surprise me if a lens teleconverter of the type mounted
to the front of a lens filter thread (NOT the type used between the back of the lens and the camera body) had some success as the front mounted optic system for your DIY Hyperstar, as the optical structure is somewhat similar, albeit afocal, to the double concave + plano convex lens you've shown in pic 1 . If you have one of these filter mounted teleconverters, it should be easy to see if it works. In principle just remove the secondary and place the teleconverter near the corrector plate to see if you can get an image on a small piece of paper held behind the teleconverter, when looking at a distant object during the daytime to make life easier. Adjust the paper and teleconverter position and focus to try to get a crisp image at what should be a vastly reduced focal length (you may need 10 hands!). You should compare the quality of this image with that with NO front optic group to see if there is a real improvement in terms of abberation.
OR ...... you could just go for a focal reducer and be happy to be somewhat faster
Best
JA