Weird Guiding Issue with OAG/Asiair Plus

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Oamaruastro avatar
I am quite new to the whole astrophotography thing, and have put together a fairly sophisticated system that I am perhaps a little under-skilled to use properly. It's been a few months since I had a chance to use my gear, since our Southern Hemisphere summer meant short nights and clouds. But the conditions were good this past week, so I trotted the gear out again and set to capturing some narrowband images.

All was going well, it seemed, until we had a meridian flip, after which the guiding went all haywire, with the Asiair telling me that it timed out waiting for the guidescope to "settle". I had fairly steady declination but the RA was off the charts and the resulting images were unusable. I paused things, and after trying a few things, I ended up aiming the telescope at a new target and starting with a new plan. These shots were fine, and guiding remained pretty good through the rest of the evening.

The next night, I tried to shoot again, and this time the guiding was fine through the Ha and Oiii filters, but when it came to Sii it again went off the rails. This has not happened before, so I don't know if it's something I'm doing wrong, or if it's something with the latest update to the Asiair (1.9). Anyone have any ideas?

UPDATE: Following the response below, I have checked my imaging train and the OAG is indeed in front of the filter wheel, so there should be no connection between the filter and the guiding.
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kuechlew avatar
Usually you place the OAG behind the filter wheel. The imaging train looks like this: Camera -> Filter wheel -> OAG -> Reducer/Flattener (optional) -> Scope.
From your statement "the guiding was fine through the Ha and Oiii filters, but when it came to Sii it again went off the rails" I would conclude your setup has filter wheel in front of the OAG. Narrowband filters reduce the brightness of the stars because they only let pass a small fraction of the spectrum. The Sii filter may have blocked too much light of your guide stars so that the guiding cam lost them.

Not sure how the Asiair handles the meridian flip. Obviously once the scope/mount performs the meridian flip the guiding loses the guide stars and has to find them again after ending up in its final position. It seems something went wrong at that point - maybe due to your filter wheel in front of the OAG. 

Clear skies
Wolfgang
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Oamaruastro avatar
Wolfgang, thank you very much–of course you're absolutely right, and indeed the OAG is in front of the EFW on my setup, so there is no connection between the filter in use and the guiding. So that makes the situation even more mysterious!
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phscale avatar
Are you using the Plan or Autorun mode?
Oamaruastro avatar
I'm using Plan mode.
phscale avatar
I don't think that you can do a meridian flip in Plan mode. With the Asi Air plus it only works in Autorun (I think!). 
Clear skies,
Paul
Oamaruastro avatar
You can definitely do a meridian flip in Plan mode–I have done so successfully in the past with no issues.
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kuechlew avatar
Ian Dixon avatar
Whenever I ran into guiding problems with my ASIair it was always the battery voltage dropping below a threshold (unknown to me).  I checked my rig for balance, backlash, guide scope problems, flexure etc (all the usual suspects) but when I dedicated a battery to the ASIair, my problem resolved itself.   It may be too simplistic, but have you looked at this aspect as a possible source of problems?

(edit) Caveat - I always shoot in Autorun mode.

CS

Ian
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Oamaruastro avatar
I am fortunate to have mains power supplying my telescope rig, so power should not be an issue. I had not considered doing Autorun–I will give that a try next time I have a clear night.
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Oamaruastro avatar
Ian Dixon avatar
I am fortunate to have mains power supplying my telescope rig, so power should not be an issue. I had not considered doing Autorun--I will give that a try next time I have a clear night.

Ah, ok - got it.  I assume everyone sets up de novo, like me, in the field.   Great that you have AC power.
kuechlew avatar
Hi,

one more: https://astrodymium.com/products/astrodymium-rings-for-samyang-rokinon-135mm-f-2-lens#

Clear skies
Wolfgang

What is this for?

Sorry wrong thread ...
Oamaruastro avatar
Just a follow up to report on what fixed my guiding issues. I had thought I might need to replace my mount's bearings, and even went so far as to get all new bearings and other gear to allow me to do this. However, I kept having to put off the project because of other commitments. The other day I watched a video from Antoine Grelin of Galactic Hunter in which he advises against using both the USB cable and the ST4 cable when connecting guide cameras to mounts, since the two cables can cause confusion. Since I had been doing that, I removed the ST4 cable from the set up and now my guiding is spot-on! What a simple solution to such a vexing problem!
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