Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Equipment

Pages: 1 | 2 | 3 | (show all)
rtomw77
Pooh-Bah
*****

Reged: 10/06/04

Loc: Deer Valley, AZ
Astro-Tech Coma Corrector in a 12" f/4.9 Scope
      #3838304 - 05/31/10 07:20 AM

There have been many threads on CN about exactly when does a Paracorr become a necessity. Most posters have felt that this occurs at f/4.5 or faster. They also have indicated that at f/4.9 a coma corrector was nice to have but that it was not a necessity. This has made me reluctant to spend $330 for a Paracorr for my Orion XT12i f/4.9 scope.

The new Astro-Tech coma corrector at the lower price of $135 renewed my interest in a coma corrector. I purchased one from Astronomics a month ago.

The instructions that come with the ATCC state that the optimum spacing from the lens assembly/shoulder to the image plane of the EP is 73.5mm. The distance from the top of the 2" eyepiece holder of the unit is 26.5mm to the image plane of the EP. I used this 26.5mm length as my goal for spacers.

The lack of an adjustable top for the ATCC limits its usefulness. You can add spacers between the bottom lens assembly and the top EP holder of the ATCC, or you can add spacers to the bottom of each eyepiece. I chose to add spacers between the lens assembly and the EP holder.

The two parts of the ATCC are connected by standard 2"/48mm filter threads. The 14mm and 28mm Baadder Hyperion fine tuning rings and a 2" color filter were picked up from OPT. Removing the glass from the filter left me with a 6mm tuning ring.

For 1.25" EP I use the 14mm and 6mm ring between the 2 parts of the ATCC. The 2"/1.25" adapter in the top of the EP holder adds another 6mm for a total of 26mm. For 2" EP I use the 28mm ring.

This 'one size fits all and use it like a barlow' approach works fairly well. Visually judging the amount of coma correction and field flattening from one combination to another is harder than I thought it would be. My subjective and unscientific estimation is that for most of the eyepieces in my collection about 1/2 to 2/3 of the edge coma effects are removed. The area of the flattest portion of the FOV increases as well.

Improvement varies from one EP design to another. Premium EP most clearly showed improvement. The exact position of the focal plane of each EP also has an effect.

2" EP used: 28mm WO UWAN; 30mm AT Titan II ED; Meade 34mm SWA 5000; and Orion 40mm Optiluxe

1.25" EP used: 9 & 11mm t6 Naglers; 15, 19, & 24mm Panoptics: Orion Ultrascopics, UO HD orthoscopics, and BO/TMB 9mm Planetary

Now for the big question: Is it worth it? I have mixed feelings about the ATCC. I think it is great for wide field low to medium magnification views. It needs more testing on a night of good seeing before I will decide to use it for high power viewing. The bottom line is that at f/4.9 the ATCC is nice to have, but it is not a necessity. For the relatively low price of the ATCC compared to a Paracorr I am happy with it.

Random thoughts in no particular order:

This is not intended as a scientific report. Someone else will have to do that. To put it another way, "Dammit Jim! I'm a Pharmacist, not an Optician!"

This thing NEEDS an adjustable top. Are you listening Atro-Tech?

You will need at least 8 to 12mm of in focus (lower focuser tube top). This distance will vary with different spacers and different EP. I ran out of in focus several times with various combinations.

Increased spacer distance has some effects. The barlow effect increases. Eye placement becomes more critical.

The ATCC dims faint objects slightly. Some of this might be due to the weak barlow effect. There is some extra glow around bright objects.

The 10% increase in focal length/barlow effect was usually only noticeable if I specifically looked for it.

At low to medium magnifications I did not notice any image deterioration. Seeing was not good enough for 200x plus testing.

So far I have not found a good combination for a 1.25"/2" Meade 4K 14mm UWA.

The Orion Helical focuser screwed all the way down just barely works in my scope with the 14mm and 28mm spacers.

Changes in spacer length of 6mm or less produced little visual change.

I will be happy and eager to hear if someone has a practical way to improve my setup.

Your mileage may/will vary.

Tom


Post Extras: Print Post   Remind Me!   Notify Moderator  
csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #3838586 - 05/31/10 11:21 AM

Tom, thank you for your thoughts on the AT coma corrector! I love reports such as yours, as I can relate your experience to what I would face with my scope.

Excellent!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Bill Weir
Carpal Tunnel
*****

Reged: 06/01/04

Loc: Metchosin (Victoria), Canada
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: csa/montana]
      #3840895 - 06/01/10 01:29 PM

Perhaps you could add one of these to it.
http://www.televue.com/engine/ProductImagePop.asp?ItemCode=PTT-2002&ItemDesc=Tunable%
It's an addon turntable built for the origional Paracorr. Probably by then you will be up to the cost of just buying a Paracorr in the first place. I think this show that you often get what you pay for.

Bill


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sky Captain
Metal Whisperer
*****

Reged: 11/07/04

Loc: Loc: Loc:
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Bill Weir]
      #3841398 - 06/01/10 06:24 PM

Quote:

Perhaps you could add one of these to it.
http://www.televue.com/engine/ProductImagePop.asp?ItemCode=PTT-2002&ItemDesc=Tunable%
It's an addon turntable built for the origional Paracorr. Probably by then you will be up to the cost of just buying a Paracorr in the first place. I think this show that you often get what you pay for.

Bill





Just happens that I have a Para and ATCC in my hot little hands right now just waiting for the sky to clear.

It so happens that the tunable top from the Para does indeed fit onto the ATCC. Problem is that the screw is a different thread on the Para and the screw on the AT body just above the threads is too big. I could see the screw thing being worked out by an industrious soul though.

I have used my ATCC in the 12" f5 Lightbridge once during a short break in the clouds. The 22 Pan was used and the stars were sharp across the field.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sky Captain
Metal Whisperer
*****

Reged: 11/07/04

Loc: Loc: Loc:
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #3841406 - 06/01/10 06:28 PM

Quote:

The two parts of the ATCC are connected by standard 2"/48mm filter threads. The 14mm and 28mm Baadder Hyperion fine tuning rings and a 2" color filter were picked up from OPT. Removing the glass from the filter left me with a 6mm tuning ring.






Nice report Tom.
Also thanks for mentioning the Baader FT rings fit. As noted in my ATCC thread, there are certain brands that won't thread on or only one end. I'll have to pick up a few for my personal use along with the adjustable top I made.


Post Extras: Print Post   Remind Me!   Notify Moderator  
sailor70623
Post Laureate
*****

Reged: 01/12/08

Loc: Ok.
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Sky Captain]
      #3841551 - 06/01/10 08:08 PM

I have a paracorr and a Baader MPCC, and am still thinking about getting the AT coma corrector. Sky Captain makes a nice top for it. But even at F4.5 I'm finding it hard to justify another coma corrector. Two I can, because on is in Mi. and the other in Ok., but 3??? Only because it might make a better CC than the Baader for visual.

Post Extras: Print Post   Remind Me!   Notify Moderator  
rtomw77
Pooh-Bah
*****

Reged: 10/06/04

Loc: Deer Valley, AZ
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: sailor70623]
      #3842095 - 06/02/10 05:56 AM

Sky Captain:

The Baader rings do fit, but the male threads on the rings are a tight fit into the female threads on the ATCC EP holder top. I get about 2 turns before it stops. This does feel safe to use though. Continued use is improving this. The Baader rings are smooth, and it is difficult to get a firm enough grip to unscrew them if they are on too tight.

The filter ring without the filter is flexible under hand pressure and is tricky to thread on. It is also easier to get stuck and harder to get off. Its male threads are also tight on the ATCC top. It fits the Baader rings and the ATCC bottom better than the ATCC top. It is a close out Antares 2" color filter from OPT. I have since found that Surplus Shed has empty 2" filter rings (M2801D) for $6.50. How well these fit is an unknown.

If you decide to make an adjustable top available to others please let me know. When I ordered the ATCC I asked if AT was planning to make an adjustable top. The salesman said "there has been some talk" about it. What this means is hard to say.

Thanks also for the info on the difficulty of using the Paracorr top.

The Orion helical focuser plus the 14mm ring shows some promise as an adjustable top for 1.25" EP. The main problem is that my scope focuser runs out of in focus quickly with this arrangement. Moving the mirror forward would cause problems with some 2" EP that require almost all of the focuser's out travel. Even with an extension tube I am reluctant to make a major forward movement of the mirror. The Orion mirror cell design has the mirror cell attached to the end ring, not to the optical tube wall.

Tom


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sky Captain
Metal Whisperer
*****

Reged: 11/07/04

Loc: Loc: Loc:
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #3843987 - 06/03/10 03:16 AM

Quote:

Sky Captain:

The Baader rings do fit, but the male threads on the rings are a tight fit into the female threads on the ATCC EP holder top. I get about 2 turns before it stops. This does feel safe to use though.




Good to know Tom, gotta find one that screws on all the way. Would be nice if AT would make some accy's that fit instead of the hit an miss that we have been going through. I still can't tell if its the threads on the CC or the tubes that's the problem.


Post Extras: Print Post   Remind Me!   Notify Moderator  
csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Sky Captain]
      #3844217 - 06/03/10 09:06 AM

Quote:

Would be nice if AT would make some accy's that fit instead of the hit an miss that we have been going through. I still can't tell if its the threads on the CC or the tubes that's the problem.





Kerry, in case Astronomics doesn't see this thread; why not give Mike a call; I'm sure he's very interested in this.


Post Extras: Print Post   Remind Me!   Notify Moderator  
rtomw77
Pooh-Bah
*****

Reged: 10/06/04

Loc: Deer Valley, AZ
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: csa/montana]
      #3846085 - 06/04/10 04:22 AM

Carol

The two parts of the ATCC fit together just fine. I think the problem Kerry is referring to is the mismatch of the 'standard' screw threads on 2" accessories from one supplier to the next. You never know for sure if a new 2" filter or accessory will fit your other 2" items until you try fitting them together. If Astro-Tech would make some tuning rings or an adjustable top for the ATCC this problem would be unlikely to occur with all AT parts.

Sometimes the problem is too much paint in the threads and all you need to do is screw and unscrew the two items until the paint wears off. Sometimes it involves the metal not being machined to standard thread dimensions. I have an Orion 2" moon filter (marked Korea) that would not fit an Orion 40mm Optiluxe 2" EP. I had to use a triangular needle file to open up the male threads on the filter before it would fit.

In my case the best fit is: ATCC lens assembly to Antares filter ring to Baader ring to ATCC EP holder. This arrangement has all the screw joints fully engaged except for the Baader ring to EP holder joint which is on only ~2 revolutions.

Tom


Post Extras: Print Post   Remind Me!   Notify Moderator  
csa/montana
Den Mama
*****

Reged: 05/14/05

Loc: montana
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #3846294 - 06/04/10 09:09 AM

Thanks Tom.

Post Extras: Print Post   Remind Me!   Notify Moderator  
rtomw77
Pooh-Bah
*****

Reged: 10/06/04

Loc: Deer Valley, AZ
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: csa/montana]
      #3888539 - 06/27/10 05:00 AM

Update

I have been trying to improve the performance of the ATCC in my scope. Checking previous coma corrector threads on CN produced an interesting item: Someone stated that a coma corrector helped to reduce the coma to a point to where your eye's own accommodation of focus would help to obtain a sharp focus at the edge of the FOV.

Uh-oh. I am very near sighted and wear trifocals. The only good things about my eyesight is that there is no astigmatism or floaters. I always flip my glasses up onto my forehead to look through an EP.

I tried viewing with a set of single vision eyeglasses that I use for binoculars with my long eye relief 2" eyepieces. Bingo! Edge correction through the ATCC improved to the proverbial "pin point stars from edge to edge" level.

My new plan is to use the ATCC with 2" EP and glasses for low power wide field views. 1.25" EP will continued to be used "bare eyed" with the ATCC since few of the 1.25" EP in my collection have eye relief long enough for use with glasses.

Tom


Post Extras: Print Post   Remind Me!   Notify Moderator  
JayinUT
I'm not Sleepy
*****

Reged: 09/19/08

Loc: Utah
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #3889196 - 06/27/10 01:43 PM

Tom,

Excellent thread. I am about ready to pull the trigger on this but may just wait for a little bit more. My 14" f4.6 may need it (haven't had it out yet) and not sure on the AT or the paracorr (it's the price thing that stops me on the paracorr).


Post Extras: Print Post   Remind Me!   Notify Moderator  
MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: JayinUT]
      #4106134 - 10/10/10 08:16 PM

any updates here? Id like to buy one of these but now am worried Id run out of travel for the focuser

Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: MessiToM]
      #4106629 - 10/10/10 11:52 PM

I pulled the trigger on the AT Coma Corrector last Tuesday. I haven't received a shipping confirmation e-mail. The coma corrector is on back-order. Well, it is an early Christmas present for myself, but I hope it arrives well before Christmas. Halloween would be nice.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
rtomw77
Pooh-Bah
*****

Reged: 10/06/04

Loc: Deer Valley, AZ
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Sarkikos]
      #4107407 - 10/11/10 11:57 AM

The only new thing I have to add is that I had to use a 3mm Allen wrench to increase the tension of my scope's Crayford focuser in order to handle the heavy weight of the ATCC with a 2" EP.

So far my favorite 2" EP in my collection for use with the ATCC is a Meade 5000 34mm SWA. The eye guard all the way down gives plenty of room for use with my glasses.

Tom


Post Extras: Print Post   Remind Me!   Notify Moderator  
MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: rtomw77]
      #4108700 - 10/11/10 08:51 PM

^ Intresting, I plan on using this mostly with my Meade 4000 QX 30mm with a 70* FOV

Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: MessiToM]
      #4108780 - 10/11/10 09:27 PM

I want to use it with my ES 14 100 Degree eyepiece for wide-field views of DSO with my 10" f/4.8 Newt Dob. But I would also like to try it with my binoviewer, ideally so I can have a wide flat coma-free field for observing planets without tracking.

Mike


Post Extras: Print Post   Remind Me!   Notify Moderator  
MessiToM
scholastic sledgehammer
*****

Reged: 12/21/09

Loc: Huntingdon PA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Sarkikos]
      #4109256 - 10/12/10 01:35 AM

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....

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [Re: Sarkikos]
      #4109447 - 10/12/10 06:27 AM

Quote:

I want to use it with my ES 14 100 Degree eyepiece for wide-field views of DSO with my 10" f/4.8 Newt Dob. But I would also like to try it with my binoviewer, ideally so I can have a wide flat coma-free field for observing planets without tracking.

Mike




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...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sarkikos
Postmaster
*****

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
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

Post Extras: Print Post   Remind Me!   Notify Moderator  
Raginar
Postmaster
*****

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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: 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Raginar
Postmaster
*****

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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
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: 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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Raginar
Postmaster
*****

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 .

Post Extras: Print Post   Remind Me!   Notify Moderator  
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!!

Post Extras: Print Post   Remind Me!   Notify Moderator  
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


Post Extras: Print Post   Remind Me!   Notify Moderator  
kwjohnson
super member
*****

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
kwjohnson
super member
*****

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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
rtomw77
Pooh-Bah
*****

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
kwjohnson
super member
*****

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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

Post Extras: Print Post   Remind Me!   Notify Moderator  
kwjohnson
super member
*****

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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!!!

Post Extras: Print Post   Remind Me!   Notify Moderator  
Metalmanstan
super member


Reged: 07/02/12

Loc: Oneonta, NY
Re: Astro-Tech Coma Corrector in a 12" f/4.9 Scope new [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)


Post Extras: Print Post   Remind Me!   Notify Moderator  
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: 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Raginar
Postmaster
*****

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!


Post Extras: Print Post   Remind Me!   Notify Moderator  
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?

Post Extras: Print Post   Remind Me!   Notify Moderator  
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: 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?


Post Extras: Print Post   Remind Me!   Notify Moderator  
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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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?

Post Extras: Print Post   Remind Me!   Notify Moderator  
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: 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
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 :-(

Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
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 :-(

Post Extras: Print Post   Remind Me!   Notify Moderator  
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!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mirzam
Post Laureate
*****

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


Post Extras: Print Post   Remind Me!   Notify Moderator  
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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
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: 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
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!!

Post Extras: Print Post   Remind Me!   Notify Moderator  
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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
12 registered and 26 anonymous users are browsing this forum.

Moderator:  tecmage, rflinn68 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 8476
Calendar Event: 05/31/10

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics