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Pointing model or MLPT?


lukepower

Question

Hi dudes,

 

the results I got after last night got me thinking about the pointing models we all seem to use here with our mounts. The last days I routinely was able to get longer exposures (10 minutes) of most objects (example: the Veil nebula), no matter which filter I was using. But last night something happened, the stars were trailing and the images are unusable. But: I made no changes to the setup (other than rebooting the computer and powering on the motors again, with their autofind). 

 

Look here:

bad.jpggood.jpg

So, now I am considering if either:

  • a) The Autofind somehow messed with the ability of the mount to track (sounds stupid to me)
  • B) Sequence did something wrong during the various MLPT runs (but it solved 4/4 and 3/4, so looks good to me)
  • c) something else changed (alright, the tube touched the roof as it closed down, but nothing strong)

I am a bit out of ideas right now. I know that my tube - or better, my main mirror - is moving a bit so that I have quite a bit of hysteresis, so that I simply cannot rely only on a complex pointing model, so i use MLPT and got really good results with it. I am using the GSC 1.1 (corrected) star catalog with Sequence, and it should work well (even if USNO A2.0 should be more precise). Hrm... I really dunno.

 

All ideas are welcome :)

 

Thanks

Edited by lukepower
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This could be almost anything!  If the scope dinged the dome, it could have just jarred something slightly loose in the set-up.  Recheck all bolts, tube rings, etc. for tightness.  With the mount switched on (and in control) I'd gently get a hold of the tube and try moving it/restraining it slightly in all directions to see if there was any play, and if there is to identify that and eliminate it.

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Hi Roger,

 

thanks for your info. I actually checked everything from the main mirror towards the secondary, and everything felt right. I only added a little more pressure on the lateral mirror holding screws (there was quite a bit of play between the main mirror and its side support). As soon as the wether permits, I'll try to get a more decent testing on the stars. I actually did a new pointing file three days ago, and - at least on the east side - it was very consistent.

 

But, just to know, are you imaging with the normal pointing file only, or using MLPT?

 

Thanks

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My mount is on order - so my advice at present is generic!  My present set-up is various 'scopes and 'scope-pairs on a home-designed plate, in turn on a Vixen Atlux.

 

If everything within your OTA is normal, this might be where the OTA attaches to the plate - or even plate-to-mount.

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