Recently I posted
about weird spikes on my old Polarex spotting scope and then I decided to replace the objective.
Two weeks ago I got an 80x500mm achromat for only $25 from a
Dutch online astro trade mart which turned out to have excellent quality. Razor sharp images @ 210x, the only difference with an apo is slight (but not annoying) blue fringing at powers above 100x.
So I let somebody lathe an adapter ring to mount this objective on the nearly 40yr old Polarex spotting scope.
Here the report with photos:
http://skysurfer.eu/polarex80.php