Flexure Compensation


#1

I’m going back to a guide scope from an OAG for simplicity and it got me thinking… What if you could have SGpro do a plate solve say every thirty minutes (have an option for time) and restart the auto guider?

I know flexure can be an issue. It was one of the main reasons I started using an OAG. I know this would be useless if you were doing extremely long exposures but in 2-5 minutes, flexure causes no noticeable star trailing. At least for me. I only noticed it when stacking my images there was drift between images and I had to crop large portions off because of the lack of overlap.

Just a thought!


#2

I would guess that it is the reduced focal length from the guide scope and maybe the same dither magnitude that is causing the issue rather than flexure. If your guide scope has a much reduced focal length you’ll want to use a smaller dither value. If you’re using the same dither value you’re now moving the scope more as compared to before with the OAG.

Thanks,
Jared


#3

I’m not having issues anymore. I was just saying if you could have SGpro do a plate solve and center every so often you could minimize the drift from flexure over time.

Regards,


#4

Wow, if there is that much drift I would doubt that flexure is the cause - and if it is there would have to be a very large amount of flexure. That would be better addressed by a more rigid system.

Personally, I hate guidescopes and 26 years of imaging have taught me that they are almost always more trouble than they are worth. OAG and/or AO for longer focal lengths and something like Pro-Track or equivalent for shorter focal lengths are a much better solution. I have found that with a well tweaked and well modeled high quality mount, I can go for 20-30 minutes at 530 mm with no drift.


#5

Ya’ll completely missed the point but thanks for the input.


#6

Not really. If you are getting enough drift so that it causes issues with image alignment and stacking in 30 minutes, and it is indeed due to flexure, then I fail to see how you could have round stars in 2-5 minute exposures. Just not possible. I think Jared is correct as to the cause and it is not likely flexure.

Having said that, I still stand by my statement that guidescopes are more trouble than they are worth. In light of my recent experiences with well tweaked systems that do not require guiding, I try never to miss the opportunity to preach the gospel of “Guiding Sucks!”. I have found that by far the best method is no guiding at all if the system can be made to do that well. Now that systems like 10-Micron and Pro-Track are available, any of their users will tell you that they are nothing but delighted to be done with guiding altogether.


#7

Again you are misunderstanding. I’m talking about a small drift over the course of the entire night. And again I had it when I started this hobby. I no longer have this problem with a guide scope. It’s just a request that would help mitigate the issue if you Had the option to re center every 30minutes or so just like auto focus.


#8

But in your first post you said

Which is it? Small or large?

in any case the solution is obvious, split your long sequence into a series of shorter ones, then the software will do the centering at the start of each sub sequence.


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