"Bump guiding" question - FU question from Roland's experience


 

For our AP1600AE with a large APCC tracking model installed, can we experiment adding bump guiding using a much smaller attached guidescope? (the 'guide every 10 seconds' approach we were discussing)


the image scale on the main CDK17 is 0.63" 
the image scale on the piggyback scope (SVX80) is approx 1.7"

Right now we can get pretty good results on 600sec exposures, but not sure if the issues we're seeing (minor issues) are seeing or tracking related. 


The reason i'm asking this is because the telescope is in Chile, so buying a compatible OAG, shipping it there, installing it, etc. is quite expensive. We already have the piggyback scope there and available so we can at least try it out if you think it would be a valid test.



--
Brian 



Brian Valente


Roland Christen
 


can we experiment adding bump guiding using a much smaller attached guidescope?
My inclination is NO, the separate guide scope will be guiding along quite nicely and show no guide errors, but after a few minutes the large scope will slowly point in a different direction than the guide scope, due to differential flexure. That slow motion will be captured on your imaging camera as a slow migration and the stars will eventually be non-round.

How long it takes for the two scopes to point in different directions depends on how much flex the large scope has. It will flex for sure, there is no doubt. If it exceeds 1 arc sec differential, you will probably see out-of round stars. Depends on the seeing of course, but Chile has great seeing and every tiny error will show immediately.

Personally I would never build up a major system like that with a 17" scope and not inherently include an off axis guider. Big Cassegrains are notorious for having flex, especially if the main mirror is heavy and supported by flotation system. It will certainly move sideways as it moves around in the sky. The secondary support will flex for sure. It's a bad system for a separate guide scope.

Rolando


-----Original Message-----
From: Brian Valente <bvalente@...>
To: main@ap-gto.groups.io
Sent: Thu, Oct 15, 2020 3:06 pm
Subject: [ap-gto] "Bump guiding" question - FU question from Roland's experience

For our AP1600AE with a large APCC tracking model installed, can we experiment adding bump guiding using a much smaller attached guidescope? (the 'guide every 10 seconds' approach we were discussing)


the image scale on the main CDK17 is 0.63" 
the image scale on the piggyback scope (SVX80) is approx 1.7"

Right now we can get pretty good results on 600sec exposures, but not sure if the issues we're seeing (minor issues) are seeing or tracking related. 


The reason i'm asking this is because the telescope is in Chile, so buying a compatible OAG, shipping it there, installing it, etc. is quite expensive. We already have the piggyback scope there and available so we can at least try it out if you think it would be a valid test.



--
Brian 



Brian Valente