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bobbyt
member
Reged: 05/14/08
Posts: 53
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does anyone have info on focuser adaptor with rack and pinion ,that can mount to back threads on c-90 so you can focus without using the whole tube barrel to focus with ,is there enough back travel to even come to focus .is there anyone even thinking of this plan. please help with some info .thanks bob
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BRisley
super member
Reged: 09/04/06
Posts: 159
Loc: SW Florida
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Bob,
You can get a LAR (Large Accessory Ring) which will give you standard SCT threads. With that you can hook up most SCT equipment (provided there is no large extension going towards the optics)
As for the backfocus range, I haven't tried adding a long extension to mine to see if it will come to focus. They do have a large focus range. I know that I could do 6' near focus with an OM1 mounted on a standard SCT T Adapter attached to the LAR and was not near the limit when doing astro work with that setup.
Brian
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albert1
professor emeritus
Reged: 01/01/07
Posts: 745
Loc: Northern New Jersey
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Hey Bob,
I saw your question and thought I was the only one going through this.
As far as I am aware there's no SCT focuser that will attach to these threads. You will need the LAR as Brian mentioned. The LAR makes the threads same size as a regular 8" Celestron or Meade back. Than you need the 1.25 visual back for the LAR. You're ready to go after that.
So it goes,
LAR
Visual back
SCT focuser
Diagonal
I hope  .
Advance warning, this LAR was tough to find. Could'nt find it at any of the usual scope stuff guy's, so, I placed a wanted ad on A-mart and someone came through. I'd suggest you take that route and save yourself some time looking. Yes, there is a LAR for the Meade ETX series, but, I was told this does not fit the C-90.
As far as the SCT focuser, another guy directed me here http://cgi.ebay.com/2-SCT-2-SPEED10-1-ROTATABLE-MICRO-CRAYFORD-FOCUSER_W0QQitemZ380052624179QQihZ025QQcategoryZ29954QQrdZ1QQcmdZViewItemQQ_trksidZp1713.m153.l1262
I have'nt tried a SCT focuser yet, but this scope sure could use something better than the helical ring. I've been told the SCT focuser should work fine with this scope. Again, I've not tried it yet. When I do I'll post back.
Hope this helps.
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Albert
XT10i w/COL and Hyperion's
1984 C90 Astro, (cool little thing)
Upgraded to 1.25 visual back from .965
made a big difference in viewing quality.
Criterion Dynascope RV6
(another cool vintage scope)
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Jay_Bird
professor emeritus
Reged: 01/04/06
Posts: 660
Loc: Nevada 36N 115W
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I was just taking an early wide field look at the double cluster and M31 with an orange tube C90, an LAR with the old ~1990 2-inch Celestron mirror diagonal (which must add almost 6" to optical path)and a 2" 40mm Plossl. While the 2" diagonal dwarfs the C90 it is still light enough to work well on a photo tripod fluid head.
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'these things stand like stone - kindness in another's troubles, courage in your own' Gordon
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clang
member
Reged: 08/06/07
Posts: 59
Loc: Chicago far SW 'burbs
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Just an FYI - the ScopeTronix website has an LAR for the Meade ETX that they say will also fit a Celestron C90.
I've got one of these C90s coming, so I'm going to have to find one too.
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If the horse don't pull you've got to carry the load.
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