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

Sanity check with new telescope setup

  • Please log in to reply
4 replies to this topic

#1 aacc66

aacc66

    Apollo

  • -----
  • topic starter
  • Posts: 1,135
  • Joined: 27 Mar 2013

Posted 02 August 2021 - 10:53 PM

I am saving to buy a Takahashi Epsilon 130 or hopefully a 160. I want to put it in tandem with the edge 9.25.  I am planning to use the 9.25 for guiding with an OAG.  Also planning to replace my guiding camera to an ASI 174mm mini.

 

Will this idea of having the Takahashi Epsilon in tandem with the Edge 9.25 insane? E.g. Balancing the mount.

 

Am I missing something here? Any suggestions on the setup/geometry? Any better idea for another telescope than the Takahashi Epsilon?  

 

I assume it should be obvious that the Epsilon will be used for imaging.

 

Thanks

 

Alvaro


Edited by aacc66, 02 August 2021 - 10:54 PM.


#2 drd715

drd715

    Viking 1

  • *****
  • Posts: 937
  • Joined: 07 Jan 2015
  • Loc: Fort Lauderdale

Posted 03 August 2021 - 12:08 AM

The 9.25 using an off axis guider will keep the 9.25 main image tracking well in relation to the OAG image, but the stability of the mirror system will not keep the 130 scope tracking very well. The mirror system has the potential to shift relative to the 130mm. While using off axis guiding on a mirror system such as the 9.25 if the mirror shifts both the off axis image and the on axis image shift the same together so tracking guide commands to the mount keep the 9.25 system guided. The guiding image on the 9.25 is not tightly locked to the 130 as the optical image from the two different scopes are generated from separate optical trains where one might shift in relation to the other.


  • bobzeq25 and premk19 like this

#3 aacc66

aacc66

    Apollo

  • -----
  • topic starter
  • Posts: 1,135
  • Joined: 27 Mar 2013

Posted 03 August 2021 - 08:11 AM

Good point.

 

Given that, would that effect be ameliorated by the at least 4 to 1 ratio between the two focal lengths (2300 mm to 500 mm) and that the nd 9.25 will have clutch in place to lock the mirror?

 

If not, how does people guide when they have multiple telescopes in a mount?  Following that logic, the short focal length imaging refractors usually use a guiding telescope, which will be the case for the edge 9.25.

 

I mean, that is that I would had done if I did not have the edge 9.25: but a guiding telescope and attach it to the setup.

 

Alvaro



#4 drd715

drd715

    Viking 1

  • *****
  • Posts: 937
  • Joined: 07 Jan 2015
  • Loc: Fort Lauderdale

Posted 03 August 2021 - 09:34 AM

If you were to use a mirror system like the 9.25 with a separate guide scope you have the potential for a small shift between the optical paths. This may be so minor that it is not a factor 99% of the time.  It is not a major concern if you are using a wider angle (shorter fl) scope.  The Off Axis guider is most helpful for long focal length scopes and narrower fields of view where the slightest differential between guiding image and camera image becomes more of a factor. Using a  off axis guider can be more challenging than a separate guiding scope, mainly due to the narrower field of view and positioning to find a good guide star.  There is much debate about a guide scope focal length as even a short guide scope works fairly well. But I prefer to keep the guide scope Focal length no shorter than 1/3 of the imaging scope Focal length  - 1/2 is what I am using most of the time. In Off axis guiding the guide focal length is the same as the imaging focal length or 1/1. 

 

The  best way to find out if your guiding system choice will work for your needs is to assemble it as you envision the different possibilities and see how they work out.  Learning by doing is the best teacher. 

 

You may find trying different settings in the guiding software parameters can "tweek" the guiding to a tighter level. Also some people have found that setting the dec slightly (very very slightly) off in polar alignment and running the dec correction in only one direction only can avoid dec backlash problems in some mounts.  The dec axis shouldn't be making many corrections anyway and they should be small. Backlash in the dec motor/ gears can cause more trouble than a perfect polar alignment combined with leaving dec corrections turned off. You have to do your own experiments here.



#5 aacc66

aacc66

    Apollo

  • -----
  • topic starter
  • Posts: 1,135
  • Joined: 27 Mar 2013

Posted 03 August 2021 - 11:38 PM

So, I had been imaging with the Edge 9.25 for about 5 years in its prime mode.  I think I had the Celestron OAG for 3 and a half years, and my MESU mount for 3 years.  The process has been  tedious to get for what I think my error is about 1 to 1.5 arcsecond peak to peak most of the time.  There are nights that the wind and/ or the seeing just don't collaborate.

 

My original intent for my question was thinking on the mount balancing by having a fast Newtonian sitting side by side with Schmidt - Cassegrain.  And maybe there was something clumsy of having the two there.  The other question was: did I miss anything?

 

Your mentioning that the mirror will flop is a possibility that I can't dismiss even if the mirror is maintained in place by the clutch. But I was under the impression that people did not wanted to use a small guiding telescope, usually 150 to 200 mm, in a long focal length imaging setup.  And I can understand that part.

 

The opposite: using a long focal length telescope as a guider seems appropriate to me.  Any small shift in the guiding should be barely noticeable in a small focal length imaging setup like the epsilon 130 or 160.

 

Did I miss anything in the guiding part?

 

Alvaro




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