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10-22-2009, 02:17 PM   #1
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astronomy telescope converted into telephoto lens?

have been looking at the possibility of converting a telescope into a Tele lens... what would make a good candidate? also plan to use this as a beginner astrophoto setup... but mainly as a telephoto lens. Ive looked at some Orion 8" R-C type telescopes... this one in particular has a 1600mm FL f/8 with 2" crayford focuser

10-22-2009, 02:32 PM   #2
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That style is about as compact as you'll probably get. In good light you should be able to focus pretty well. Of course it won't be a carry around unit.
A lot of folks use that size and type scope for astro work. It will work well with a modded webcam too.
10-22-2009, 02:34 PM   #3
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is there a decent adapter you would recommend for the pentax k mount for the 2" focuser, or will i need to ghetto rig something
10-22-2009, 02:40 PM   #4
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The Orion 8" R/C comes with 1" and ' extension tubes to adjust focus position of the camera. All that is needed is a T mount for the camera.
I would not advise cobbling until you get the hang of how it all will work.

10-22-2009, 02:40 PM   #5
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15.8 lbs for OTA alone is pretty heavy. 1600 mm fl for terrestrial use might be a bit much, specially on hot and humid days.
What would you have to add to make it a telephoto, it is a mirror lens to start with, right?.

Man I am a slow typist, Orion makes a 2" T-adapter that fits right in the Grayford focuser, for about $ 40.00.

Cheers. Mike.
10-22-2009, 02:51 PM   #6
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The tubes are needed to be sure the camera is within the range of focus of the focuser. The R/C's are built different.
10-22-2009, 02:53 PM   #7
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And as a side note. You'll need one heck of a solid tripod. At 1600mm your heartbeat would look like the SF quake of 1906.
10-22-2009, 02:58 PM   #8
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Roger that. I use Orion 120 EON with a crap load of focuser travel.
With 40 mm long gutted tele-converter it focuses down to 25 feet.

Cheers. Mike.

10-22-2009, 03:05 PM   #9
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Don't use near an airport.
10-22-2009, 03:06 PM   #10
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not sure on the tripod yet... wont be gettting into dso's or anything cause dont plan on getting a tracking mount... unless a cheapy cg5 would do the trick... hrm... i had a 12" meade OTA stuck ontop one of these suckers a couple years ago.... never got into photograpgy though
10-22-2009, 03:16 PM   #11
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Wind will be your big problem. That and any strong ground vibration, like a freeway.
10-22-2009, 03:26 PM   #12
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What about just spending the money on a Bigma, would probably be less of a headache to use, just a thought..
Unless you are hard set on astro also.

Cheers. Mike.
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