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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]
      #5593874 - 12/29/12 07:49 AM

Agena sells a neat adjustable extension tube here .

http://goo.gl/f58si for the short version.

Or this one for the long: http://goo.gl/JTAUd

Glad we could help!


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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]
      #5597082 - 12/30/12 10:47 PM

I thank you all for the great info and help. I have ordered both of the products that I need: the Parfocalizing rings from farpoint and the ATCC from astronomics. Hopefully I will have a clear night sometime so I can take it out and use it!! One more question, can testing the ATCC and setting the Parfocalizing rings be done during the day time?

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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: Metalmanstan]
      #5597325 - 12/31/12 02:37 AM

Quote:

I thank you all for the great info and help. I have ordered both of the products that I need: the Parfocalizing rings from farpoint and the ATCC from astronomics. Hopefully I will have a clear night sometime so I can take it out and use it!! One more question, can testing the ATCC and setting the Parfocalizing rings be done during the day time?



I don't see why not as long as the target is far enough away that you are essentially using infinity focus--maybe a building a mile away?


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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: Starman1]
      #5609225 - 01/06/13 09:04 PM

Ok. So I got my paracorr in the other day. My last question is about collimation. Do I collimate it with the paracorr in or out? When I have the paracorr on I can't get my Cheshire collimator in the whole length.

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johnnyha
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Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Metalmanstan]
      #5609281 - 01/06/13 09:39 PM

Out.

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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: johnnyha]
      #5610403 - 01/07/13 03:08 PM

Alright. So I checked out the coma corrector a couple of minutes ago and it looked great on a telephone pole at a good distance away. I tried to focus on a hill way beyond the pole in the backround and I couldn't get it to focus. Any suggestions? And because I cant get it to focus on the hill will it not focus on stars/deep sky objects at night?

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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: Metalmanstan]
      #5610425 - 01/07/13 03:21 PM

Quote:

Alright. So I checked out the coma corrector a couple of minutes ago and it looked great on a telephone pole at a good distance away. I tried to focus on a hill way beyond the pole in the backround and I couldn't get it to focus. Any suggestions? And because I cant get it to focus on the hill will it not focus on stars/deep sky objects at night?



The hill is closer to infinity focus, which is where celestial objects focus, so yes, it won't focus on stars.
I presume you didn't have enough inward focuser movement to allow you to reach focus.
Some possible cures:
--mount the primary mirror farther forward (this may be doable, but often requires counterweights be added to the bottom of the scope)
--lower-profile focuser
--re-mount focuser 1/2" lower by using other side of tube and simply rotating around. This may require significant re-working to finder, altitude trunnions, etc. But all it takes is time and a hole saw.
--If the focuser drawtube bottoms out on the focuser and there is still a centimeter or so of drawtube above the focuser body, the drawtube might be easily trimmed shorter to allow more inward travel. This might entail cutting a slot in the focuser body to allow the setscrew to go lower than the top of the focuser. On my first Moonlite, the drawtube's minimum height was actually below the top of the focuser.


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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: Starman1]
      #5610503 - 01/07/13 04:11 PM

Ok. So are there any other threads that would show me how to go about doing these suggestions? I've been into astronomy for only about a year so I'm still fairly new to this and the *BLEEP* thing is that there aren't really any people into astronomy around me either :-(

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csrlice12
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Reged: 05/22/12

Loc: Denver, CO
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Metalmanstan]
      #5610536 - 01/07/13 04:30 PM

You know, you've mentioned something there I think all of us have noticed. There's little in the ways of education when it comes to astronomy equipment. Buy an EQ mount, sure, here's the 3-page instruction book--good luck. Anyone who's bought a dob knows about those Dob Base instructions (Makes IKEA instructions look like a pro job). It'd be nice to have some videos of "heres how you align an EQ Mount"; Here's how to use setting circles on an EQ Mount. Here's how you collimate a dob/newt with a 1) Cheshire/collimation cap 2) Catseye system 3) Glatter/Blug/Tublug system. Here's how to safely remove the primary from a dob/newt, heres how to replace a newt/dob spider veins/secondary and adjust. It would really be nice if there was a community college around that would offer a course like this, call it an "Astronomy Equipment 101" or something. I'd pay for a class that would do that for me as I'm one who learns better by doing then by a book.

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Starman1]
      #5610540 - 01/07/13 04:33 PM

Quote:


Some possible cures:
1.mount the primary mirror farther forward (this may be doable, but often requires counterweights be added to the bottom of the scope)
2.lower-profile focuser
3.re-mount focuser 1/2" lower by using other side of tube and simply rotating around. This may require significant re-working to finder, altitude trunnions, etc. But all it takes is time and a hole saw.
4.If the focuser drawtube bottoms out on the focuser and there is still a centimeter or so of drawtube above the focuser body, the drawtube might be easily trimmed shorter to allow more inward travel. This might entail cutting a slot in the focuser body to allow the setscrew to go lower than the top of the focuser. On my first Moonlite, the drawtube's minimum height was actually below the top of the focuser.



As for instructions how to do these things, you'd have to do some Google searches. They may exist, but probably only for #1. #2 would be fairly easy with the help of one of the focuser manufacturers--after all, they do this every day.
1. This may or may not be possible. If the mirror cell has a groove into which the end of the steel tube inserts, it cannot be moved forward without cutting the steel tube. If the cell is held in place with bolts through the tube and the end of the tube is bare, you can simply drill new holes 1/2" up and remount the mirror cell. Then add a weight to the bottom of the tube to compensate for moving the center of gravity up.
I suspect you have the former situation, so moving the mirror forward might be possible but only about 1/8" or so, using the collimation knobs--the main knobs are loosened and the locking knobs are tightened--this moves the primary mirror forward a tad.
2. You can measure the height of your focuser from the tube up when the focuser is racked in all the way. Moonlite, JMI, Starlight Instruments, Wyorock, Kine Optics all make lower profile focusers. If your current focuser is on a "platform" that lifts it up, say, 1/2", you can get a lower spacer from one of the above companies, such as Moonlight, and lower your current focuser 1/4" or more. Couple this with #1, and you're beginning to get within reach of focus.
3. For this one, you'd drill a new hole in the opposite side of the tube, but down 1/2" from the current focuser hole. Then, you'd re-mount your focuser there, rotate the tube around, reattach the finder and altitude trunnions (all operations necessitating drilling new holes) and you'd have the focuser where it needs to be. This isn't really hard, but requires some time, planning, measurements, and a proper-sized hole saw for metal.
4. If there is still some focuser drawtube sticking out above the focuser when it is in all the way, the focuser can be dismantled, the tube removed, and the end cut off. You'll have to drill and tap a new hole farther into the drawtube for the setscrew, and you will probably have to cut a notch in the top of the focuser to allow the new setscrew to go further into the body of the focuser. This is a machinist's job, and cannot be done with home tools unless you are a machinist. If you replace your focuser with a Moonlite CR-1, for example, this is already done for you.

Since #3, and #4 require some prior experience with metal tools and some idea of what you're doing, my recommendations are to start with #1, and then move on to #2 if that's not enough.


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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: Starman1]
      #5611052 - 01/07/13 10:31 PM

I'll have to agree with you csrlice12. It seems like the stuff I have to do will be costly because Ill end up breaking something. The nearest professional shop is Highpoint Scientific, which is about 3 hours from here :-(

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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: Metalmanstan]
      #5611340 - 01/08/13 03:04 AM

Be reassured, I also found it a pain to get this coma corrector working...

If the coma corrector and extensions are fully sunk into the drawer tube to the shoulder of the supplied visual adaptor then I would only expect focus to move in by 10mm or so. It would be worth checking to see how far the focus has actually moved, by trying to focus on closer objects. This will given some idea of how much adjustment you need and what approach to take.

Good luck!


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Mirzam
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Reged: 04/01/08

Loc: Lovettsville, VA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: cjc]
      #5611387 - 01/08/13 05:57 AM

If you use 1.25" eyepieces consider something like this.

Also, if you need to adjust the Paracorr top to a lower setting in order to reach focus, just do it. The effects on coma correction will not be that major.

JimC


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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: Mirzam]
      #5611518 - 01/08/13 08:42 AM

This is interesting and would work, with the right spacing, as a fixed visual interface for 1.25" eyepieces with the ATCC which will screw directly on to the 48mm filter thread. With a 2" parfocalizing ring, you could set the focuser travel arbitrarily.

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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: cjc]
      #5611714 - 01/08/13 10:51 AM

Quote:

Be reassured, I also found it a pain to get this coma corrector working...

If the coma corrector and extensions are fully sunk into the drawer tube to the shoulder of the supplied visual adapter then I would only expect focus to move in by 10mm or so. It would be worth checking to see how far the focus has actually moved, by trying to focus on closer objects. This will given some idea of how much adjustment you need and what approach to take.

Good luck!




This sounds like the scope is a SkyWatcher dob. SkyWatcher dobs sold in the US have a focuser which has a drawtube larger in inside diameter than 2" and uses separate adapters for 1.25" or 2" eyepieces.
Unfortunately, the 2" adapter has a 1-15/16" opening in the bottom and while that's fine for 2" eyepieces, 2" accessories longer than eyepiece barrels (barlows, coma correctors) will not insert all the way until they rest on the adapter.

This prevents the accessories from working and requires a significant inward focuser movement. It's a bad design.

If it is a Sky-Watcher (aka Synta) dob, you should sand out the bottom of the 2" adapter so 2" accessories will slide through. The bottom hole doesn't even have to be round as long as 2" accessories pass through. This can easily be done with sandpaper while you're watching TV. This alone would probably allow the coma corrector to reach focus.


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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: Starman1]
      #5612041 - 01/08/13 02:18 PM

Alright guys, I solved the problem. I took out the primary mirror and placed felt pads below it to give it a little more push to the secondary. Then I Did Don's suggestion and I shimmed down the adapter to get even a little bit more. After that I could focus in on the mountain miles away and I even did it with a barlow attached to a 10mm to see if I could get even closer. Problem solved. I thank everyone for the suggestions, couldn't of done it with out this awesome community!!

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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: Metalmanstan]
      #5612551 - 01/08/13 07:13 PM

Well done! I look forward to your report on the difference it makes.

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