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

Setting up the GSO coma corrector

  • Please log in to reply
190 replies to this topic

#176 StarCurious

StarCurious

    Viking 1

  • *****
  • Posts: 568
  • Joined: 24 Dec 2012
  • Loc: York Region, Ontario

Posted 23 September 2019 - 11:19 AM


Yes, the extenders I used all had standard 48mm threads.

John,

 

Good.

 

What is the length of the GSO CC 2" eyepiece holder, broken down as the leftmost section in the picture on Post #3?

 

EDIT: I used the picture in Post #3, I measured on screen the 19mm is 70mm long, the GSO CC 2" eyepiece holder is 175mm long. Therefore, approximately the GSO 2" eyepiece holder may be (19*175/71=) 48mm.  How far off am I?

 

MORE EDIT: Your GSO CC 2" to 1.25" adapter is 10mm high (?), With that added, the 1.25" eyepiece holder is now (10=48=) 58mm above the focuser 2" draw tube.  My set up needs to be 61mm above.  That means I need 3mm more focuser inward travel than standard set up?

Thanks,

Joseph


Edited by StarCurious, 23 September 2019 - 11:38 AM.


#177 precaud

precaud

    Fly Me to the Moon

  • *****
  • topic starter
  • Posts: 5,010
  • Joined: 05 Dec 2012
  • Loc: north central New Mexico

Posted 23 September 2019 - 11:37 AM

Joseph,

 

I don't know, I no longer have one of these CC's, mine was stolen a couple years ago. If the lens is properly placed, then what you do above it is totally up to you, as long as the spacing dimensions are satisfied, and it comes to focus.



#178 StarCurious

StarCurious

    Viking 1

  • *****
  • Posts: 568
  • Joined: 24 Dec 2012
  • Loc: York Region, Ontario

Posted 23 September 2019 - 12:04 PM

John,

 

Thank you for your excellent presentations and illustrations throughout this thread.

 

Joseph



#179 Baatar

Baatar

    Mariner 2

  • -----
  • Posts: 292
  • Joined: 26 Mar 2019
  • Loc: Geneva, Switzerland

Posted 25 October 2019 - 05:43 AM

I thought it would be useful if I include a link here to a recent thread that I started in relation to the GSO coma corrector.

 

https://www.cloudyni...extension-47mm/

 

 

Please note that this worked for me with SW 10" collapsible dob, and also for Dave with Z10 dob.


Edited by Baatar, 25 October 2019 - 05:44 AM.


#180 shubham_chandravanshi

shubham_chandravanshi

    Lift Off

  • ****-
  • Posts: 12
  • Joined: 25 Oct 2020

Posted 26 October 2020 - 02:03 PM

Hey guys, I have just ordered a GSO 8" F/4 as my first scope with an Explore Scientific Exos-2 PMC-8 WiFi Goto Mount. I am thinking to buy the GSO 2" CC with proper spacers. I read this whole thread today and I want to sincerely thank all of you guys for taking me from zero knowledge on how to use CC (I thought it was just like a barlow) to letting me feel a lot more confident about buying it and being able to use it. I will be using it for visuals as well as for AP.

I will be going the path to add the proper spacers to reach the 75mm backfocus distance and parfocalize all my 1.25" eyepieces. My main concern is with using barlows with this CC. Where do I need to put a barlow in this configuration? It would be a great help if you could help me figure this out for both 1.25" and 2" barlows.

And while I was reading this thread, near the end, I read someone addressing not to buy this CC for AP at all! Is this really true? I live in India and this is the only eyepiece at my disposal.

Thanks in advance for your help!
Clear Skies!

Edited by shubham_chandravanshi, 26 October 2020 - 02:05 PM.


#181 MellonLake

MellonLake

    Apollo

  • *****
  • Posts: 1,414
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted 06 November 2020 - 07:29 PM

Precaud

 

Thank you for this thread.  I just set up my new GSO coma corrector with the 19mm spacer and it went very nicely thanks to you, the XT10 telescope would not have reached focus without this spacer (even though I have a great deal of infocus). 

 

The coma corrector leads to very refractor like views (with diffraction spikes on bright stars).   It works well to clean up the coma in my F/4.7  no more comets in the outer field of view. 

 

I set up my 2" APM UFF 30mm with a parfocal ring.  The balance of my eyepieces are very close to parfocal so I don't think I have to adjust them at all (even though I have a bunch of parfocal rings on the way).

 

Thanks Again!  


  • precaud likes this

#182 Adam Long

Adam Long

    Mariner 2

  • -----
  • Posts: 258
  • Joined: 19 Sep 2019
  • Loc: Sheffield, UK

Posted 17 February 2021 - 05:01 AM

Does anyone have a value for the focuser in-travel required for the GSO CC?

 

Have read this thread and several others but can't see it stated anywhere, just that it is somewhere between the 14mm of the Paracorr 2 and 32mm of the Explore Scientific...



#183 Adam Long

Adam Long

    Mariner 2

  • -----
  • Posts: 258
  • Joined: 19 Sep 2019
  • Loc: Sheffield, UK

Posted 09 March 2021 - 04:25 AM

Measured the GSO last night - focuses at around 12mm in-travel with the CC vs prime focus.

The CC shoulder sits 43mm high so corrected prime focus is about 32mm (43-12) further out than originally.

 

I'm using a Baader 28mm spacer (the 19mm seems unavailable in Europe) which gives about 76mm from CC unit to top of the GSO 2" EP holder. My lowest 1.25" adapter adds another 7mm, but I need a better night to assess spacing vs correction.



#184 belliott4488

belliott4488

    Vostok 1

  • *****
  • Posts: 171
  • Joined: 05 Oct 2020
  • Loc: MD, US

Posted 09 March 2021 - 07:44 AM

Measured the GSO last night - focuses at around 12mm in-travel with the CC vs prime focus.

The CC shoulder sits 43mm high so corrected prime focus is about 32mm (43-12) further out than originally.

 

I'm using a Baader 28mm spacer (the 19mm seems unavailable in Europe) which gives about 76mm from CC unit to top of the GSO 2" EP holder. My lowest 1.25" adapter adds another 7mm, but I need a better night to assess spacing vs correction.

By "12mm in-travel" do you mean that you rack the focuser in by 12mm compared to where it reaches focus without the CC?



#185 Adam Long

Adam Long

    Mariner 2

  • -----
  • Posts: 258
  • Joined: 19 Sep 2019
  • Loc: Sheffield, UK

Posted 09 March 2021 - 12:17 PM

Exactly that.


  • belliott4488 likes this

#186 Adam Long

Adam Long

    Mariner 2

  • -----
  • Posts: 258
  • Joined: 19 Sep 2019
  • Loc: Sheffield, UK

Posted 23 March 2021 - 12:53 PM

I'm using a Baader 28mm spacer (the 19mm seems unavailable in Europe) which gives about 76mm from CC unit to top of the GSO 2" EP holder. My lowest 1.25" adapter adds another 7mm, but I need a better night to assess spacing vs correction.

Drilled/ filed a groove in the top of the CC 2" holder so the low-profile Moonlite sits nicely flush and only adds 2.5mm to the stack.



#187 Adam Long

Adam Long

    Mariner 2

  • -----
  • Posts: 258
  • Joined: 19 Sep 2019
  • Loc: Sheffield, UK

Posted 26 March 2021 - 09:58 AM

I wouldn't advise the Baader spacer, it's pushing the limit of the spacing but mainly the threads just won't mate properly (which adds to the length). I got a set of Svbony M48 extension tubes (5, 10, 15, 30mm) which mate perfectly and mean you can set up spacing correctly for both visual and photo use.



#188 belliott4488

belliott4488

    Vostok 1

  • *****
  • Posts: 171
  • Joined: 05 Oct 2020
  • Loc: MD, US

Posted 26 March 2021 - 12:55 PM

I wouldn't advise the Baader spacer, it's pushing the limit of the spacing but mainly the threads just won't mate properly (which adds to the length). I got a set of Svbony M48 extension tubes (5, 10, 15, 30mm) which mate perfectly and mean you can set up spacing correctly for both visual and photo use.

I got a set of 2" filter threaded spacers from Astromania that work very well with the GSO CC (mine is branded High Point, but I believe it's the same). The threads match all the 2" threaded adapters I have with the exception of a 2" barrel to 42mm T2 adapter from Antares.

 

I haven't yet had a chance to determine the optimal combination of spacers, but if I can do that, I'll post my results here.



#189 Waynosworld

Waynosworld

    Viking 1

  • *****
  • Posts: 785
  • Joined: 22 Oct 2020
  • Loc: Vancouver Washington

Posted Yesterday, 11:00 PM

It took me 6 pages of reading this thread before I figured out what the spacer on the Coma Corrector was for, I guess I am slow as when installed on the Coma Corrector it moves the CC lens closer to the secondary mirror, such a simple concept but I guess I am slow.

 

I did not read every reply, I just recently in the last month bought A GSO Coma Corrector, I did not have enough inward/in-travel focus on my 14.5" F4.5 dob and my 12 dob, I was short by just a little that the spacer might fix, but recently I bought a Feather touch low profile focuser for my 16" F/4.42 dob, now when I put the GSO CC in and use my 2" Meade 32mm SWA 4000 series eyepiece in it without the required 75mm space between the CC lens and the lip of the eyepiece it came into focus in the middle of travel, I have not tried it with the 75mm(I actually have 80mm right now without the extra spacer in the CC), so from what I read put my 2" Meade 32mm SWA 4000 series eyepiece in the extended CC using the 35mm extension I have which works out to 80mm, then put the whole thing in my scope, find where it comes into focus and lock the focus assembly in place, then using a 2"/1.25" adapter I can put my 1.25" eyepieces and pull them out the amount needed to come into focus, if they need to go inward then I will need to either find a shorter extension for the CC or maybe use my TV 2"/1.25" in-travel

adapter which might get me inward a couple mm maybe only 1mm(78/79mm), but I do have the Feather touch 2'/1.25" adapter that does get me to 76/77/78mm depending how I use it.

 

I have not tried it this way with the 75mm between the CC lens and the shoulder of the eyepiece yet as it worked with about 45mm between them but nothing improved the view so I do not know anything yet, I posted what I had to say so if you know I am doing it wrong please enlighten me.

 

I do listen when it sometimes don't appear that I am listening as I don't always understand yet, but eventually I will get it as I am only slow, faster than some, slower than others, it only took me 6 pages to figure out what the spacer was for included in the GSO Coma Corrector box lol.gif


Edited by Waynosworld, Yesterday, 11:04 PM.

  • belliott4488 likes this

#190 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 50,395
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted Today, 06:04 PM

The spacer in the GSO is to enable you to place the focal plane of the eyepiece at the requisite distance of 75mm from the CC lens.

It is at this position where, when you focus the scope, the CC will be at the correct place in the light cone from the primary to correct coma properly.

 

If you use the CC at a different distance, and focus the scope, the CC will not be at the optimum distance from the primary and coma correction will

not be optimized.  You might get less coma correction at the edge of the field.

 

Since you bought the coma corrector to correct coma, you might as well use it correctly.

 

And there is a side benefit:

Once one eyepiece is optimized and the CC is in the right place in the light cone, all other eyepieces can simply be pulled out relative to the CC lens until in focus, and that will keep the CC

in the correct place in the light cone from the primary and result in all of your eyepieces focusing at the same place in the focuser's travel.

 

Since the GSO does not have a helical top like the Explore Scientific HRCC or the TeleVue Paracorr, the way to accomplish that with the GSO is to start with your eyepiece that requires

the most in-focus without the CC and optimize that eyepiece first.  Every other eyepiece will need to be pulled out of the CC top to achieve focus and it really helps to add parfocalizing rings to the eyepieces

so that when they are reinserted they are already almost perfectly focused.  Following that, you only will need a mm of travel in the focuser.  AND, you can optimize any new eyepiece you buy simply by pulling it out of the CC top until it is in focus.

 

The focal plane in many brands have known positions, so if you are uncertain and you own a TeleVue, Baader, Pentax, or Explore Scientific eyepiece, we can tell you the necessary distance from the CC lens to the shoulder of the eyepiece

that is needed to optimize it.


Edited by Starman1, Today, 06:06 PM.


#191 Tom62e

Tom62e

    Mariner 2

  • *****
  • Posts: 248
  • Joined: 25 May 2014
  • Loc: Scottsdale, AZ

Posted Today, 06:27 PM

The spacer in the GSO is to enable you to place the focal plane of the eyepiece at the requisite distance of 75mm from the CC lens.

It is at this position where, when you focus the scope, the CC will be at the correct place in the light cone from the primary to correct coma properly.

 

If you use the CC at a different distance, and focus the scope, the CC will not be at the optimum distance from the primary and coma correction will

not be optimized.  You might get less coma correction at the edge of the field.

 

Since you bought the coma corrector to correct coma, you might as well use it correctly.

 

And there is a side benefit:

Once one eyepiece is optimized and the CC is in the right place in the light cone, all other eyepieces can simply be pulled out relative to the CC lens until in focus, and that will keep the CC

in the correct place in the light cone from the primary and result in all of your eyepieces focusing at the same place in the focuser's travel.

 

Since the GSO does not have a helical top like the Explore Scientific HRCC or the TeleVue Paracorr, the way to accomplish that with the GSO is to start with your eyepiece that requires

the most in-focus without the CC and optimize that eyepiece first.  Every other eyepiece will need to be pulled out of the CC top to achieve focus and it really helps to add parfocalizing rings to the eyepieces

so that when they are reinserted they are already almost perfectly focused.  Following that, you only will need a mm of travel in the focuser.  AND, you can optimize any new eyepiece you buy simply by pulling it out of the CC top until it is in focus.

 

The focal plane in many brands have known positions, so if you are uncertain and you own a TeleVue, Baader, Pentax, or Explore Scientific eyepiece, we can tell you the necessary distance from the CC lens to the shoulder of the eyepiece

that is needed to optimize it.

Hi.  Not to hijack this thread from the OP, but I use a GSO Coma Corrector with a GSO 6" F/4 Imaging Newt.  How do I know if the Coma Corrector is in the best optimal distance from the camera's sensor?  Do I just take a 10-second exposure and analyze the image for oval stars?  Is there a more precise way of doing this? 

 

I'm buying some fine tuning spacer rings and perhaps a variable spacer so that I can dial it in perfectly.  Because from what I was told by AgenaAstro, the recommended 20mm spacer is just a rough starting point based on user feedback - and that fine tuning is almost always required.

 

Do I just keep taking images between the installation/removal of spacers until I see the image with the roundest stars around the perimeter - or is there a more precise way to dial it in?

 

Thanks.




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






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics