в инете я нашел, что у одного самодельшика с похожей идеей
"Some years back I picked up a projection TV lens. It has a focal length of 22" and 4" of clear aperture, making it a f/5.5. The cell contains 4 lenses in 3 groups (2;1;1) with baffles between each group.
I built a make-shift telescope using the cell, a piece of 4" PVC sewer pipe, a cap, and a 2" dob focuser I has kicking around.(picture below) Visually it work great with a 20mm plossl EP, but I havn't tried it yet for AP."
22 дюйма - это длинный фокус?











