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Projection lens

Started by 2dogs7, 03/18/2015 09:45PM
Posted 03/18/2015 09:45PM | Edited 03/18/2015 09:46PM Opening Post
Hi All, I recently had a friend give me some lenses out of a old projection TV. Does any one have experience working with these lenses? Can they be used in any way to make a scope? I know some people used projector cells to make scopes. Just wondering...
Posted 03/19/2015 05:32AM #1
I've always had TERRIBLE luck with trying to use projection lenses for astronomy imaging. They are just optimized for a completely different application. Things like absolute field, F#, color correction, resolution AND the light goes "the other way" which DOES make a giant difference! I worked in optics all my life, so not surprised regarding the disappointment. Lenses were all over the place at work and finding one that would be useful for astronomy was RARE. (I worked at Bausch & Lomb back when it was a true full-capability optics house and then Eastman Kodak.) The most I ever got out of the scrap bin was very nice unmounted Hastings magnifying lenses and some discarded Pyrex blanks, small mirrors...stuff like that. Tom Dey

29-inch Dob in a dome
36-inch upgrade soon
LUNT 80/80 solar scope
FLI 6803 cam
APM 100mm APO Binos
JMI RB-16 Night Vision Binos
Zeiss 20x60 IS binos
Posted 03/19/2015 05:33AM #2
Many years ago I was given a "projector lens" and put it in a piece of PVC pipe and made a reducer and slide focuser for the other end. It was about 90mm or so, probably an f/4.5 to f/5. With a wide field 35mm ep i got some of the best views I have ever had of the Andromeda galaxy and M33 up at Mt. Pinos. Probably in the mid 70's if I remember correctly. Do the same and you might have a jewel!

Walt
Posted 03/19/2015 05:50AM #3
I just read Walter's experience there and can indeed see where it would perform nicely as a rich field. 7mm pupil at 12X mag would be very comfortable and not push the "diffraction limit" at all. I still have a finder made like that with a lens jammed in a PVC tube and an ancient Edmund's unmounted Kellner used at very low mag. It's one of the best finders I ever had! So try it to see if it's worth using! Tom Dey

29-inch Dob in a dome
36-inch upgrade soon
LUNT 80/80 solar scope
FLI 6803 cam
APM 100mm APO Binos
JMI RB-16 Night Vision Binos
Zeiss 20x60 IS binos