Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

C90 - best 1.25" option?

accessories Maksutov Celestron
  • Please log in to reply
14 replies to this topic

#1 αLyraen

αLyraen

    Sputnik

  • -----
  • topic starter
  • Posts: 32
  • Joined: 11 Aug 2017
  • Loc: Austin, TX, USA

Posted 07 September 2017 - 07:32 PM

I recently got a C90 (one of the rubber armored spotting scope versions from maybe the late '80s or early '90s) in pretty good condition. First light was a couple of nights ago; I was out walking the dog and saw that the neighbors' kids around the corner had a lemonade stand set up, so after enjoying some lemonade and chatting with the neighbors I grabbed the C90 on a photo tripod and shared a quick peek at Saturn and the full moon with the family and another neighbor family that was hanging out in the driveway.

 

I'm pretty happy with the C90 and am looking forward to using it as a quick look grab-and-go, but I'm not thrilled with the .965" to 1.25" diagonal that it came with. It's a 45° erect image one, and while I'm sure it'll do nicely for terrestrial use, I think I could do better for astronomical use. Part of the reason I chose Saturn and the moon and not, say, M13 as targets was because they were both low to the sky. (Jupiter was low to the sky as well, but hopelessly lost behind a tree.) I could probably be reasonably happy with a .965" to 1.25" mirror diagonal, but it would be nice to have the versatility of using other 1.25" accessories.

 

In my brief research on the subject, it sounds like there was something called the LAR (Large Accessory Ring), which isn't made any more and is hard to find. I can't find any pictures of what the LAR looked like, or a good description of how it worked, but there are a couple of more modern options that seem like they would be useful, both marketed as adapting Meade ETX threads (which supposedly the old C90s used as well) to standard SCT threads:

 

http://www.baader-pl...nding-ring.html

https://www.meade.co...sct-thread.html

 

How similar are these to the LAR? Is there a particular reason I'd pick one over the other? Also, a quick test with a 1.25" barrel showed that it wouldn't fit through the bore back of the MCT, so that means that once I put a 1.25" visual back on one of those adapters, an accessory would potentially bottom out against something, as opposed to passing straight through on an SCT with a full 2" bore. Is that going to be problematic?

 

Are there other options besides a .965" to 1.25" diagonal, or one of the above adapters, that I haven't considered? Does anybody have a favorite .965" to 1.25" diagonal, if I decide to go that route?



#2 photoracer18

photoracer18

    Vanguard

  • *****
  • Posts: 2333
  • Joined: 02 Sep 2013
  • Loc: Martinsburg, WV

Posted 07 September 2017 - 07:59 PM

You hit it on the head. The LAR gives you an adapter with the thread of the SCT visual back so you can use SCT accessories.



#3 mvas

mvas

    Apollo

  • -----
  • Posts: 1337
  • Joined: 27 May 2015
  • Loc: Eastern Ohio

Posted 07 September 2017 - 08:01 PM

Meade may not manufacture the "LAR".

But I think scopestuff, and others, have an adapter that converts to 2" SCT Threads.

Just make sure you clearance between larger diameter tubes and the focuser knob.


Edited by mvas, 07 September 2017 - 08:02 PM.


#4 αLyraen

αLyraen

    Sputnik

  • -----
  • topic starter
  • Posts: 32
  • Joined: 11 Aug 2017
  • Loc: Austin, TX, USA

Posted 07 September 2017 - 08:03 PM

The LAR gives you an adapter with the thread of the SCT visual back so you can use SCT accessories.

 

So it's not substantially different from the more modern thread adapters? I couldn't find a picture, so I wasn't sure if it operated on a different principle from the options I linked above.



#5 αLyraen

αLyraen

    Sputnik

  • -----
  • topic starter
  • Posts: 32
  • Joined: 11 Aug 2017
  • Loc: Austin, TX, USA

Posted 07 September 2017 - 08:05 PM

Just make sure you clearance between larger diameter tubes and the focuser knob.

 

This actually focuses more like an SLR lens, by rotating the front of the OTA. It takes getting used to, but it does mean there's no focuser knob to worry about clearances with, and no possibility of mirror flop. :)



#6 αLyraen

αLyraen

    Sputnik

  • -----
  • topic starter
  • Posts: 32
  • Joined: 11 Aug 2017
  • Loc: Austin, TX, USA

Posted 07 September 2017 - 08:07 PM

And thanks for the pointer to the ScopeStuff ring:

 

http://www.scopestuff.com/ss_etxa.htm

 

Unfortunately, that explicitly says it *doesn't* fit the C90. So I guess the information I had heard about the ETX and C90 threads being the same was incorrect.



#7 Southland

Southland

    Lift Off

  • *****
  • Posts: 16
  • Joined: 29 Jun 2009

Posted 07 September 2017 - 11:42 PM

The Meade 07036 ETX Back Cell Adapter fits my Orange C90 just fine.  I have it installed right now.


  • Don W likes this

#8 jgraham

jgraham

    Hubble

  • *****
  • Posts: 19821
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 08 September 2017 - 10:17 AM

I have also tried an ETX adapter on my orange-tube C90 and it works fine. However, I eventually took it off and just went with a conversion diagonal. This turned out to be a good match for 1.25" eyepieces that I use with this little scope.



#9 αLyraen

αLyraen

    Sputnik

  • -----
  • topic starter
  • Posts: 32
  • Joined: 11 Aug 2017
  • Loc: Austin, TX, USA

Posted 08 September 2017 - 06:14 PM

I found this thread:

https://www.cloudyni...-mak-rear-cell/

which says the ETX and C90 threads have the same pitch, but the C90 thread diameter is 35mm and the ETX thread diameter is 34.6mm. I measured my threads calipers and the OD was 35.2mm. I could definitely see how you might get lucky and get a C90 with a slightly narrow rear cell thread, and an ETX to SCT adapter with a slightly wide inner thread, but I could also see how you could get unlucky, hence the incompatibility disclaimer on the SS ring.

It sounds like the Celestron LAR generally worked on the ETX threads, so I wonder why nobody is copying the LAR dimensions.

#10 Bigern

Bigern

    Vostok 1

  • *****
  • Posts: 157
  • Joined: 18 Aug 2016
  • Loc: Miami Fl.

Posted 09 September 2017 - 10:23 AM

I use one of these on my C90.

http://www.ebay.com/...o4AAMXQY8JRgS44



#11 αLyraen

αLyraen

    Sputnik

  • -----
  • topic starter
  • Posts: 32
  • Joined: 11 Aug 2017
  • Loc: Austin, TX, USA

Posted 09 September 2017 - 12:22 PM

Bigern, I think that is the winner! Simple and obvious, I feel silly for overlooking an option like that. It wouldn't focus any better or worse than a 1.25" SCT visual back, and had the added benefit of potentially being useful for any other vintage .965" hardware I might run into in the future.
  • Bigern likes this

#12 jallbery

jallbery

    Vanguard

  • *****
  • Posts: 2467
  • Joined: 01 Nov 2015
  • Loc: Southeast Michigan

Posted 10 September 2017 - 12:30 AM

Certainly the eyepiece adapter is one way forward.  I'd probably opt for a hybrid .965/1.25 diagonal if I were going that route, though.

 

You may want to read this entry from Uncle Rod's blog:

http://uncle-rods.bl...ides-again.html

 

If nothing else, it's worth it to see a photo of a 2" diagonal on a C90!

 

 

>>a quick test with a 1.25" barrel showed that it wouldn't fit through the bore back of the MCT

A 0.965" diagonal won't fit in the rear baffle tube of a C90, either.  The rear baffle is about 17mm , which is ls about 0.67".   In either case, you should use a visual back long enough for the barrel of the diagonal you are using.

 

>>Are there other options besides a .965" to 1.25" diagonal, or one of the above adapters, that I haven't considered?

The company Uncle Rod mentions above (https://www.telescopeadapters.com/ ) currently offers an ETX visual back that should work fine with most older C90s (they warn that some have oversized threads).   See https://www.telescopeadapters.com/content/5-meade-etx-telescope-camera-adapters   

 

So instead of purchasing an ETX LAR-type adapter, you can just use a 1.25" visual back and diagonal.  This would be my prefered solution.  Note, however, that Telescope Adapters is currently closed due to the approaching hurricane.

 

And as far as the scopestuff ETX adapter saying that it does not fit the C90, they may be referring to the current C90: the current c90 uses a larger thread that is compatible with the Nexstar 127mm Mak and many other Synta-built small to mid-sized Maks (note that Orion seems to be moving to SCT threads for their larger Maks).  So they need a different adapter than older C90s and ETXs.

 

And since we are on the subject, I believe that the Celestron Nexstar 4, 4i and 4SE versions of a 102mm Mak (scopes that have ETX-esque flip mirrors for a built-in diagonal and rear port) all use the ETX thread standard on their rear port.  But the SLT 90, 102, and 127 versions (none of which have a flip mirror) use a larger-size thread.



#13 WoodyEnd

WoodyEnd

    Vanguard

  • -----
  • Posts: 2049
  • Joined: 21 Mar 2016

Posted 31 October 2017 - 09:39 PM

I just picked up a black C90. The visual back will take 0.965 accessories and has outside threads about 1 3/8" (35mm).  I am not sure what the purpose of these threads are but I see that you can use a LAR adapter so that you can use standard SCT visual backs.  One question I have is, is it better to use a hybrid diaganol for 1 1/4" EP's or should I hunt down a LAR?

 

Another question is what parts do I need to adapt this scope as a telephoto lens? Will this T-adapter work?

 

http://agenaastro.co...ter-93635a.html



#14 WoodyEnd

WoodyEnd

    Vanguard

  • -----
  • Posts: 2049
  • Joined: 21 Mar 2016

Posted 31 October 2017 - 09:59 PM

A little searching found that Baader makes a LAR type adapter.

 

http://agenaastro.co...xstar4-c90.html

 

Maybe this ETX T-mount adapter could work with a C90.  Can you lap the threads until it would fit? 


Edited by WoodyEnd, 31 October 2017 - 10:09 PM.


#15 Im2bent

Im2bent

    Sputnik

  • -----
  • Posts: 27
  • Joined: 23 Aug 2018

Posted 14 January 2019 - 06:31 PM

I used the meade adapter on my orange c90 works perfectly. I got it here. https://www.amazon.c...0?ie=UTF8&psc=1

Yes I know this was posted a year ago.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: accessories, Maksutov, Celestron



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics