Oh, a Pentax telescope thread! Nice. I don’t have a Pentax telescope, but I do have a Pentax 1000mm f/8 camera lens refractor w/M42 screw mount & an integrated 60power(about) eyepiece & 90degree prism. Yes, it is a camera lens, even including a manual stop-down aperature from the said f/8 to f/45. At the given 60power, I have split double stars to 2.5arcseconds. With such good performance, does anybody have a clue where I could find an eyepiece giving about 150power(about 7mm eyepiece) with an integrated 90degree diagonal w/M42 lens mount attachment. Yeah, yeah, I know. I’m talking about something that hasn’t been made for 50-55 years?
You could pretty easily disassemble a T-adapter or dead M42 lens and mate the threaded part to a diagonal. Though i doubt (depending on how the Pentax focuses, is it a rack and pinion like a big 1000mm Olympus Zuiko?) it will reach infinity focus. Some people have used long camera lenses as scopes but usually with the tube assemblies and other internal lenses discarded. Might want to do that to a valuable vintage lens. I had a 100mm f/5.6 refractor made up of a Leitz 560mm telephoto lens, but only because the lens cell conveniently unscrewed from the lens body like a telescope lens and cell. Also, some lenses, even long ones with few elements may depend on some of the internal lenses for aberration correction. I used a couple converted spotting scopes as astro scopes, a B&L ED unit worked beautifully, a Kowa Fluorite did not.