larryhample

Darrin, it's 8+ years after the last posting, so hopefully you or someone else (perhaps Bob Atkins) sees this... Has anyone considered screwing a 1.25" high-quality concave/diverging 'filter' (multi-coated doublet, maybe similar to my Celestron SCT focal reducer) into the front of a diagonal (mirror/star or erect-image) in order to extend the back-focusing range of a telephoto lens? Unfortunately, I'm a theory guy, not a DIY guy. I actually already own one of the Kenko LENS2Scope adapters for my Canon EF lenses that Bob mentions here: Lens to eyepiece adapters - Turn your Lens into a Telescope - Bob Atkins Photography . The image quality is surprisingly high, better than my TeleVue Ranger (70mm objective) with high quality 1.25" eyepieces (albeit with either a crappy star or erect-image diagonal -- my better quality ones busted or were lost). The problem is the narrow 42 degree apparent field-of-view and persnickety eye placement required w/the Kenko. Yes, I could buy better diagonals, but the idea is to not have to carry a separate spotting scope. The Kenko seems to use a small diameter concave/diverging lens element first in the optical path in front of the erect-image prism followed by the narrow FOV (Kellner?) 10mm eyepiece. My idea is to duplicate that optical system, except using off-the-shelf astronomical telescope components. The sticking point is how to put a concave/diverging lens element into a 1.25" filter housing. Any ideas? I'd use either the rear-lens cap idea, or cannibalize a (metal) lens mount off of a cheap or non-functioning lens. In either case, another issue is how to make sure the axis of my proposed optical assembly is aligned with and perpendicular to the optical axis of the lens. Larry PS -- Not that it matters, but I'm not a photo.net newbie. I've just been inactive a while and exist under multiple IDs (a problem I'd like to fix).