Jump to content


Photo

Question - Piggyback AT72ED on 8SE OTA

  • Please log in to reply
5 replies to this topic

#1 ben2112

ben2112

    Cloud Magnet

  • *****
  • Posts: 1149
  • Joined: 12 Jul 2012
  • Loc: North Charleston SC

Posted 05 October 2013 - 04:33 PM

As part of my AP equipment which includes the VX mount, I want to get the AT72ED for capturing images of galaxies and other DSOs. But I also want to use an autoguider. So, I have thought about doing a piggyback mounting of the AT72ED to my 8SE OTA. When using the AT72ED to capture, I would use the 8SE OTA as a guide scope, and vise a versa for using the 8SE OTA. Couldn't get my head around how to do it. Then I ran into this post. Click Here It's for the ST80 but wondering if it would work for the AT72ED.

#2 nodalpoint

nodalpoint

    Apollo

  • *****
  • Posts: 1168
  • Joined: 03 Jun 2013
  • Loc: FEMA camp

Posted 05 October 2013 - 06:44 PM

Way too much weight for the mount. Get a 50mm guide scope for the refractor and forget the idea of putting the refractor on the SCT.

#3 ben2112

ben2112

    Cloud Magnet

  • *****
  • Posts: 1149
  • Joined: 12 Jul 2012
  • Loc: North Charleston SC

Posted 05 October 2013 - 06:56 PM

But from my understanding, a 50mm guide scope is limited to 1500mm focal length. The 8SE OTA is 2032mm. That is why I was thinking of doing the piggyback of the AT72ED. And just use one scope as a guide scope and the other as the imaging scope. The ST80 is 3lbs while the AT72ED is 5lbs. 8SE OTA is 12lbs + 5lbs + 2lbs for the camera has a total weight of 19lbs. Just add 2lbs for various stuff and you are still under 30lbs. And close to the 2/3 limit for AP use. It might not be perfect, but it should work.

But my question has to do with stability of mounting the AT72ED to the 8SE OTA using the method in the post I linked to in the first post.

#4 RTLR 12

RTLR 12

    Aurora

  • *****
  • Posts: 4559
  • Joined: 04 Dec 2008
  • Loc: The Great Pacific NorthWest

Posted 05 October 2013 - 07:52 PM

I used the ADM MDS (Mini Guide Scope Kit) shown here to mount my Onyx 80mm scope on top of my C8 OTA mounted on one of my CG-5 mounts.

Attached Files



#5 ben2112

ben2112

    Cloud Magnet

  • *****
  • Posts: 1149
  • Joined: 12 Jul 2012
  • Loc: North Charleston SC

Posted 05 October 2013 - 08:41 PM

Cool. Thanks RTLR 12. That is exactly what I was looking for. That is the route I am going to go then.

#6 mclewis1

mclewis1

    Thread Killer

  • ****-
  • Posts: 10892
  • Joined: 25 Feb 2006
  • Loc: New Brunswick, Canada

Posted 06 October 2013 - 09:55 AM

The 1500mm comment about the 50mm guidescopes is just a suggestion, not a hard and fast rule. It's not like the autoguider suddenly doesn't work, it's more about the accuracy which if you are working with a CG-5/AVX class of mount isn't going to be great anyways (effective yes, but even the 50mm autoguider will generally be more capable than the mount itself).

For the vast majority of imaging there is also no way you should be considering imaging with a C8 at it's native focal length ... that will be waaay too tough (too slow which requires longer exposures, too long a focal length which puts too much pressure on the accuracy of the mount). At minimum I would use an SCT .63x focal reducer to get the focal length down and speed up on your C8.

Another benefit of the smaller 50mm autoguider is that you could use it with a small refractor (which is IMHO a much better option for imaging on an AVX mount). Yes you could use the C8 as an autoguider instead but with it's excessive weight and moving mirror it's not even remotely an optimal solution for autoguiding.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics