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Equipment Discussions >> Equipment

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Sarkikos
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Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: MessiToM]
      #4109570 - 10/12/10 08:44 AM

MessiToM,

Quote:

That does make sense^ ill put jupiter at the edge of my fov and watch it drift through the ep but it only looks good toward the center anyway....




That would depend on how well-corrected the eyepiece is, also. But in general, with the coma corrector the planet's image should be sharper beyond the usual diffraction delimited area for the telescope.

Mike


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Sarkikos
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Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Jon Isaacs]
      #4109591 - 10/12/10 08:56 AM

Jon,

Quote:

I am not sure how well coma correctors work with binoviewers. The spacing between the focal plane of the eyepiece and the coma corrector is important/critical in optimizing the correction of coma and it seems to be a matter of a few millimeters. The MPCC with it's spacing needs and the Paracorr with it's included tunable top clearly demonstrate this.

But with a Binoviewer, the distance from the coma corrector to the focal plane of the eyepiece is several inches, this seems like a real problem. Ideally, you could have a coma corrector for each eyepiece but obviously that is impractical.

Something to think about before diving in...




Well, I've already dived in, because I ordered the AT Coma Corrector last week. But it's on backorder, so I still have a chance to come out of the water.

My intended use of the ATCC is not solely dependent on binoviewing. I'm flexible. If binoviewing is not possible with the corrector, I'll go back to cyclops mode. I'll just try some of my wide-field EPs, maybe with a Barlow or lens cell screwed on for higher power. Binoviewing planets is great, but monoviewing with a wide flat field in a non-tracking Newt should also be very nice.

But I will definitely try the corrector with my binoviewer to see if I can get it to work. Of course, dual CCs is out of the question for several reasons: (1) cost, (2) weight, (3) my binoviewer is not a 2".

Clear & Steady Skies,
Mike


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audioaficionado
scholastic sledgehammer


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Sarkikos]
      #5287217 - 06/24/12 06:40 PM

Any updates on this? Christmas 2010 was 18 months ago

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Raginar
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Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: audioaficionado]
      #5288749 - 06/25/12 04:45 PM

It took 6 months to get mine To be honest, it's not a great CC. I end up with flat stars but they're not perfectly round.

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audioaficionado
scholastic sledgehammer


Reged: 05/24/12

Loc: Medford, Orygun, USA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Raginar]
      #5288978 - 06/25/12 07:25 PM

Thanx for getting back. Guess I'll cross this one off the list. Flat is the most important to me, but CC is close second.

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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: audioaficionado]
      #5289062 - 06/25/12 08:05 PM

It might be interesting to those contemplating this coma corrector that you only have to achieve the best coma correction in one eyepiece to figure out the best correction for all your eyepieces.
1) mess around with the spacers (internal or external) until you are sure one eyepiece is well-corrected all the way to the edge. If the star image at the edge is perfectly round, even if it is out of focus, if you can focus it, this is the proper setting because now you are only accomodating field curvature.
You can also adjust the correction with the star image out of focus if you dial the image in to be completely round at the edge of the field, because then you will be able to focus it without coma.
2) Freeze the focuser. Focus all your other eyepieces by adjusting the spacers. All your eyepieces will be parfocal when the spacers are adjusted correctly. This assures all eyepieces will have the correct distance to the focal plane of the lens.
You may not be able to get every eyepiece perfectly focused, and that's OK, but try to get them all to focus at the same point for best correction.


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Raginar
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Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Starman1]
      #5289820 - 06/26/12 10:00 AM

You can see my examples on my AB link. The last M57 did NOT have the CC installed; every other picture does. You'll notice that in every picture with, there is about 1/4 of the picture that has stars slightly elongated. Some people have said it is due to it not being aligned in the focuser, but I can't seem to get it to align up well enough to bing every star into focus.

I'm using what AT recommends for spacing; I've done everything between +/- 10mm of 75mm and it doesn't seem to matter all that much.

Again, I'm just doing AP with it. No eyepieces.


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Raginar]
      #5290142 - 06/26/12 01:16 PM

Try playing with the spacing. You may find a slightly different spacing yields better correction. The empirical results show you don't yet have the proper correction.

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Raginar
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Reged: 10/19/10

Loc: Rapid CIty, SD
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Starman1]
      #5290237 - 06/26/12 02:05 PM

Thanks, I will .

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Metalmanstan
super member


Reged: 07/02/12

Loc: Oneonta, NY
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Raginar]
      #5551160 - 12/02/12 10:10 PM

Alright, I know this thread might be over and hidden in a closet somewhere, but has anyone else bought or used this and if they did, would you recommend it? A solid review of its possibilities would be great!!

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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Metalmanstan]
      #5551168 - 12/02/12 10:19 PM

I have one still in the box. I got all the spacers I think I will need but haven't had a chance to do anything with it. Skies have been incredibily poor for the last month or so. I was hoping to get in at least one good night's evaluation before the snow flies but it's not looking promising.

dan


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kwjohnson
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Reged: 03/27/11

Loc: Minneapolis, Minnesota
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: dan_h]
      #5551864 - 12/03/12 11:20 AM

I received the GSO version a couple days ago and am waiting for the clouds to clear.

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kwjohnson
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Reged: 03/27/11

Loc: Minneapolis, Minnesota
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: kwjohnson]
      #5552855 - 12/03/12 09:16 PM

Here's my informal review of the GSO version, since I don't know enough to do anything more technical.

I've had a 10" f/4.7 scope for a couple years. Using an ES100 20mm by itself, there's plenty of coma in the outer half of the field and definite field curvature. In practical terms, if I focus on one half of the double cluster framed in the 20mm, the other is out of focus and full of flares.

Using the GSO Coma Corrector, stars seem coma free almost to the edge, and the field is significantly flatter. Both clusters are pleasant to look at without refocusing.

Same results with the ES100 14mm and 9mm. Same results on M39. Nice stuff.

Definitely worth $120 on sale from Agena Astro.

Here's the backstory. In the spring I bought a C6 as a grab and go and suddenly noticed how much coma there was in the dob and how little of the field my eyes could keep in focus. I bought a Paracorr II, which definitely improved the view. I never return stuff, but I sent the Paracorr back because of balance issues and wobble in the focuser. I've since figured out how to adjust my MoonLite to handle the GSO and a big ES100. I also didn't like one more adjustment (the tunable top) in addition to sliding weights around and locking the altitude tension to change eyepieces so the scope wouldn't move. Knowing what I know now, maybe returning the Paracorr was stupid. But after returning it I bought a C8 EdgeHD, which is a lovable scope for the view and portability and ease of use on the Twilight II mount. Maybe not the light grasp of the 10" dob, but the whole field is crisp and coma free.

Until I tried the GSO I was ready to get rid of the dob, but for $120 I'm seeing significant improvement. The dob will be staying.

I had about an hour outside tonight in great transparency but bad seeing, so this is a for-what-its-worth review. Big lesson? This is all a learning process.


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rtomw77
Pooh-Bah
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Reged: 10/06/04

Loc: Deer Valley, AZ
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: kwjohnson]
      #5553751 - 12/04/12 10:55 AM

Kevin

Do you have naturally good eyesight, or do you use glasses or contacts? I have to view through glasses for best results when using wide field EP in the ATCC.

Tom


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kwjohnson
super member
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Reged: 03/27/11

Loc: Minneapolis, Minnesota
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #5553879 - 12/04/12 12:25 PM

Tom--I wear glasses but take them off for the scope. I'm nearsighted in my viewing eye.

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cjc
sage


Reged: 10/15/10

Loc: Derbyshire, England
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: kwjohnson]
      #5555046 - 12/05/12 03:31 AM

My thoughts can be found here, Astro-Tech/Altair Astro/GSO Coma Corrector and User Guide

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kwjohnson
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Reged: 03/27/11

Loc: Minneapolis, Minnesota
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: cjc]
      #5555250 - 12/05/12 08:09 AM

Thanks for that added detail, Chris. Nice writeup. I'll have to play around with the spacing as well and see if I can get even better results.

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Metalmanstan
super member


Reged: 07/02/12

Loc: Oneonta, NY
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: kwjohnson]
      #5555599 - 12/05/12 12:34 PM

I will now be getting one of these for Christmas!!! Thanks for the info everyone!!!

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Metalmanstan
super member


Reged: 07/02/12

Loc: Oneonta, NY
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope [Re: Metalmanstan]
      #5591497 - 12/27/12 05:18 PM

So I will be purchasing the ATCC in a couple of days, my question is, where do I purchase the additional spacers to make the needed length on the focuser?

Edited by Metanmanstan (12/27/12 05:19 PM)


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope [Re: Metalmanstan]
      #5591516 - 12/27/12 05:31 PM

You need spacers on the eyepieces, not the focuser on the scope. The point is to bring all your eyepieces to focus at the same point in your focuser travel.
Parfocalizing rings are available from ScopeStuff, Farpoint, and several other sources.
In the event that the eyepiece needs to be pulled out too far for comfort, a simple barrel extender added to the eyepiece will allow the eyepiece to be pulled out far enough to properly position a parfocalizing ring. Many retailers have barrel extenders. Once the barrel is extended, the parfocalizing ring enables you to position the eyepiece properly.

It's important to start with the eyepiece that needs to be closest to the lens in the coma corrector. If you have no clue which one that would be, it's likely to be your lowest-power 2" eyepiece with the largest field stop. You would put it in, focus the scope, look at the edge and evaluate the coma or lack thereof. Pull the eyepiece out 1/8", refocus and evaluate the edge again. Worse? Then you've found your "closest to the coma corrector lens" eyepiece. Better? Try another eyepiece. You want to start with whichever eyepiece is closest to the coma corrector lens when it has the best star images at the edge. Every other eyepiece will focus slightly farther out--hence the parfocalizing rings.

Once you've got that eyepiece, focus the scope. Add parfocalizing rings to all your other eyepieces. Then, insert another eyepiece and slide it out until it's in focus and slide the parfocalizing ring down until it touches the ATCC. Lock that ring in place. Do this for all your eyepieces, and when you insert every eyepiece it will automatically be at the right distance from the coma corrector.

And, you'll have very little focusing to do after that--maybe a tiny bit of touch up is all.

And if you add another eyepiece, it'll be EASY to find the proper setting for it.


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