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TMB92 or C5 w/FR for use w/BIPH

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#1 prestonrich

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Posted 18 September 2012 - 07:21 PM

For browsing wide MW star fields I've narrowed my choice down to the the TMB92/f5.5 (has adjustable infocus) and the C5 w/6.3FR for use w/my BIPH. Which may provide the most satisfying views?

#2 StarStuff1

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Posted 18 September 2012 - 11:03 PM

Depends on what your main targets are. Either will work fine but I would reccomend the refractor if you like to view larger objects. That f ratio will work well natively. Add a focal reducer and you have a killer combo.

For smaller targets your C8 with a focal reducer will do a nice job.

#3 StarStuff1

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Posted 18 September 2012 - 11:15 PM

OK, with a little more thought why even think about spending the $$$ for the TMB (nothing against TMB) when you already have a very nice f/6.25 80mm apo? With a .5 focal reducer you should get a nice wide fov with the BIPH. If you want an even wider fov get a used/new Lumicon 80mm SuperFinder. It is f/3.7 or so. With a ,5 focal reducer it will give about 3X. A pretty darn wide field for the MW. A short focal length C-mount lens makes the view even wider.

#4 prestonrich

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Posted 19 September 2012 - 09:58 AM

Thanks, StarStuff, but my Onyx 80 refractor simply doesn't have sufficient infocus to allow use w/the BIPH.

#5 prestonrich

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Posted 19 September 2012 - 10:01 AM

Would the SuperFinder have enough infocus?

#6 StarStuff1

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Posted 21 September 2012 - 02:09 PM

I had a SuperFinder a couple of years ago. It easily reached focus with my IIE when not using a star diagonal.

BUT, it just dawned on me the the Lumicon SF has only a 1 1/4-in focuser tube and I think your BIPF is made for a 2-in focuser.

One alternative is to cut some off the end of the Onyx tube.

Another alternative rises if you have some ATM skills. You can get creative. Starting from the bottom is a 50mm f/4 bino objective with a focuser made from aluminum pipe fittings, a 70mm f/4 bino objective and tube with an Orion helical focuser, and an 80mm f/3.7 UO objective combined with a PVC tube and swap table 2-in focuser.

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#7 prestonrich

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Posted 21 September 2012 - 02:50 PM

WOW, now that's creative, but for me...3 thumbs is one too many ;-)

#8 PEterW

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Posted 01 February 2013 - 08:27 AM

Just picked up an 80mm f4 finder from APM, with 2" helical focusser. Best bit is I got the tube shortened to prevent any "will it focus" trouble. Just use a 2"barrel extension as required. Just over a kg in weight. Now waiting for the clouds to take a break.

PeterW






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