we can continue the discussion here for the sake of sharing those common issues
A simple homemade Ivanoff corrector (as the original model by Ivanoff - Rebikoff…) can be ok for narrow FOV like 30 deg; but I’m not sure how it will fare with exact distortion and the above issue of “entrance pupil movement”.
One more “makeshift trick”:
You can use a small dome - say 2 inches - over a smartphone objective; for example the one of Raspberry camera 3 (little metal rectangle, Autofocus)
It works decently because the smartphone objective is built as “pinhole” or “pancake”, without the large front lenses typical of camera wide angle objectives.
It needs to be dead-center in the dome, calibration will be accurate only for one focus position, and has some substantial field curvature (the focus is different for center and corners).
Are coming out some new, very small “pancake” wide-angle objective, like Canon RF 16mm 2.8 and 28mm 2.8, that may tolerate working with a small dome; like the smartphone objective above; i haven’t tried them yet.