Quote:
Originally Posted by cventer
How cirtical is it that the guidescope is aligned to the imaging train OTA ?
With the very wide 50 and 80 mm guidescopes we are now able to use, guidestars can be fairly far off axis from where camera is pointing.
How much of an impact does this typicaly have on guiding ? Is it better to ensure they are pointing at pretty much same part of the sky ?
What are the symptoms of not having them aligned ?
I aks becuase recently when Imaging objects nearer to SCP i am having eratic guiding, whereas objects nearer to dec zero seem to have no guiding issues.
2 nights ago I was imaging an object near scp. I could not seem to get round stars even though PHD was showing straight lines on the graph. Seemed like I was getting image rotation. I then switched to my internal guide chip on the ST-2000XM and guiding was perfect.
I double checked all connections on my external guidescope and camera. All solid so no movement or flex. Is it possible that guding on stars further off axis from imaging plane near SCP impacts guiding more than stars closer to imaging plane ?
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It isn't that critical that the guide scope and imaging scope have parallel axes. If they don't your polar alignment has to be better. I've seen posts elsewhere where they got good results for high declination targets with the guide scope axis 10-15 deg off the imaging scope.
The closer you get to the poles the harder it is to guide because there is less pixel movement in RA, so having the guide scope pointed away means any tracking error is easier to pick up. However it also puts the centre of any field rotation where the guide star is located which may be outside your imaging area, which is why we get back to needing good polar align.
Even then you might have to limit the exposure time.