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Equipment Discussions >> Refractors

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careysub
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: Terry Fowler]
      #6055914 - 08/31/13 11:46 AM

Quote:

Well jrbarnett - you just cost me $369. I was planning to get one of the 80mm Orion short tube refractors I've been seeing for about $100, but now I have a C80ED on the way and it should arrive on Tuesday. Oh, since I was going to spend $100 anyway I guess you only cost me $269! Now to find a mount worthy of it.




I, OTOH, already have a ST80 (picked up for $80 as a second from Orion) and the 102GT that has been much discussed recently (both great deals), and a 90mm Meade OTA (800mm FL, which I guess is a DS2090) which I picked up for $25 at RTMC two years ago.

The 102GT has a chromatic aberration index of 2.70 (seeing has how it is really a 97mm scope as another poster has revealed), which suggests only a little would be visible (I'll have to take it out with the Moon to see), and it has larger aperture.

As attractive as the C80ED deal is, it feels like gilding the lily to add yet another refractor in the same aperture range. If compactness matters the ST80 has that covered, if low CA is called for the 102GT should do pretty well there, and people are liking its optical quality, and the Meade 90mm fills the gap in size between them with a compromise CA (much better than the ST80, a little worse than the 102GT).

Has anyone compared the CA in the C80ED and 102GT directly?

Can anyone make a case for getting this in addition? I am inclined not, but the scopes won't be available for long so would I get "non-buyers remorse" later?

Edited by careysub (08/31/13 12:24 PM)


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PeterR280
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Reged: 05/27/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: careysub]
      #6055953 - 08/31/13 12:13 PM

I have the C102GT (2 of them, I have no idea why I bought 2,) the C80ED and the Barska 80mm triplet. They were all bought based on comments on this site. My favorites are the C102GT and the Barska, although I did replace the focuser with a GSO 2 speed Crayford style. I had originally bought the focuser for the C80ED.

To answer your question, the C102GT is close to the C80ED as far as CA. I may have a very good copy of the C102GT. The Barska shows no color. I used all 3 on Venus. You can see a gradient of color very much like a prism with the C102GT and the C80ED. The C80 was better corrected but not by much. Venus looked white with the Barska. On Saturn, C102GT beats both scopes but that would be expected based on the size, the image is brighter and you can go to higher magnification. Saturn looks the same on the C80ED and the Barska. Both the 80mm scopes began to give out beyond 170-180 magnification. The C102 could go to over 200 magnification and as I said the planet was definitely brighter. I was using a TeleVue 3-6mm zoom for Saturn.

On Star tests, I got similar patterns to the above pictures for the C102GT. I showed less violet than the picture above. The Barska also does well. When focused at 200x, the star is bright white in the center and a clearly defined white airy disc is visible on the Barska. The C80ED had a more poorly defined star test. I know the star test is not always accurate with refractors. I may have a poorer copy of the C80ED. I know some people show better results.


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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061580 - 09/03/13 08:07 PM

Ok the GSO arrived today with the c80ed adapter. I have no idea how you were able to remove the huge threaded ring though, the focuser part is easy but the big ring is really on there.

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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: calypsob]
      #6061602 - 09/03/13 08:29 PM

It should screw off

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PeterR280
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Reged: 05/27/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061626 - 09/03/13 08:42 PM

Keep the mounting dovetail on the ring. It will give you something to hold on to. I attached a picture to show the threads that screw on to the tube.

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PeterR280
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Reged: 05/27/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061635 - 09/03/13 08:45 PM Attachment (101 downloads)

The picture didn't post.

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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061660 - 09/03/13 09:03 PM

ok yea that is the C80 adapter right? I have been doing battle with this piece for over an hour now. It is really on there. I assume this piece is threaded to the thread that will adopt to the c80ed adapter. http://www.flickr.com/photos/70374000@N08/9669503356/

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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: calypsob]
      #6061664 - 09/03/13 09:05 PM

the picture is the Barska ring that you are trying to remove. the small dovetail screws onto it.

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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061667 - 09/03/13 09:07 PM

Ok thanks. So is the large knurled thread and the dovetail piece on solid ring? Or are they 2 separate rings?

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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061670 - 09/03/13 09:07 PM

you have the wrench on the wrong thing. unscrew the ring with the screw hole tht hold the dovetail

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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: calypsob]
      #6061675 - 09/03/13 09:08 PM

WOOO! I got that bad boy off, thanks again! LOL

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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: calypsob]
      #6061676 - 09/03/13 09:09 PM

You were right though, I backed up the second wrench onto the dovetail area and held the tube with the first wrench.

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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061677 - 09/03/13 09:09 PM

take off the knurled ring. you want to unscrew the one inch ring behind it. it screws onto the main tube. you want to remove the ring with the 4 holes for the dovetail

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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6061750 - 09/03/13 09:56 PM

Peter, are you using a GSO guidescope or an orion on the focuser mount? Im trying to figure out if I can mount my orion guide scope on the focuser now. I got everything hooked up thanks to your advice.

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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: calypsob]
      #6061755 - 09/03/13 10:01 PM

i am uisng the C80 finder and mount. i dont have a guidescope on it. did you get the Agena finder bracket? any standard finder mount should work.

The scope looks much nicer with the new focuser, doesn't it? It makes a nice compact package.


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calypsob
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6062152 - 09/04/13 05:38 AM

No, no agena adapter. I think I am going to drill a hole in the center of my orion adapter and mount it on the focuser with an m4 screw. It looks a million times better now, here is a quick video http://www.youtube.com/watch?v=EeWZcUNtmb0

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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: calypsob]
      #6062379 - 09/04/13 09:52 AM

I was going to drill a hole in my generic adapter too but got lazy. Look at the instruction for the finder mount adapter on the Agena web site. It shows what hole to use on the focuser.

The telescope looks great. Congratulations.


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calypsob
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Reged: 04/20/13

Re: Cheapest 'ED APO' yet? (Barska Magnus) new [Re: PeterR280]
      #6062841 - 09/04/13 02:53 PM

Thanks it works great. In regards to the gt102 c80 and barska 80 i believe 2 achromats are being compared to a triplet. If this is the case the triplet will always win in color accuracy against any doublet, especially at f7. Each element in the triplrt brings RGB to focus on a separate element while a doublet usually focuses red and attempts to combine green and blue on the second element, the blue that falls out of the spectral capabilities of the second element go out of focus on the image plane thus creating blue chromatic abberations. The c80ed may be a great deal but its expensive for a doublet. The barska magnus 66 ed and 80mm ed are the cheapest apochromatic triplets on the market.

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Scottxray
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Reged: 08/06/10

Re: Cheapest 'ED APO' yet? (Barska Magnus) [Re: calypsob]
      #6064451 - 09/05/13 01:28 PM

Peter,

I also picked up a Barska 80 and was wondering about the total change in distance of focuser travel after mounting the GSO and C80 adapter?

The original Barska focuser looks to have 3.1 inches of travel ( just like the GSO ) but the adapter rings and two focusers have somewhat different lengths? I would assume
that there is somewhat more IN focus travel, but less out?

I don't want to get in a position of having to use a 2" diagonal with a camera or have the focuser racked nearly all the way out to achieve focus. Have you found any problem achieving proper focus with a camera?


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PeterR280
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Re: Cheapest 'ED APO' yet? (Barska Magnus) [Re: Scottxray]
      #6065110 - 09/05/13 07:58 PM

I am not using a camera yet. Only visual so for. I will probably set up a camera at some point.

It looks like you lose about .75 inches on the focuser itself. It is sitting closer to the tube. Travel on the GSO is 2.8 inches.


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