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Great Declination, mediocre RA

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8 replies to this topic

#1 nateman_doo

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Posted 18 September 2019 - 10:45 PM

I wonder if anyone else has this problem.  Even with the polemaster.  I mean yea I shouldn't be complaining, but I wonder if there is something I can do to help with the RA.  I have the Belt mod for the EQ6.

 

Good Declination.PNG



#2 17.5Dob

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Posted 18 September 2019 - 11:07 PM

In an "Ideal Situation" that should be the case. If you nail your PA with a PoleMaster, Dec is just along for the ride. Your main drive train is only moving in RA, and any piece of grit, not to mention the overwhelming affects of PE, accounts for 90% of drive corrections


Edited by 17.5Dob, 18 September 2019 - 11:09 PM.


#3 rgsalinger

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Posted 18 September 2019 - 11:27 PM

If you are using the 8" RC and the QHY174 camera then you have something wrong with your configuration in PHD. Some quick math shows your reported image scale at around 3 arc seconds per pixel which is way off what it should be. The camera has 5.86 micron pixels and the focal length is 1600 mm. So, un-binned the guider image scale is .76 arc seconds. You'd have to bin it way up to get the numbers that you are showing. In turn that makes the RA guiding much better. On the other hand, perhaps on this night you were not using the OAG.  Then, I'd wager that with a guide scope this is as good as it gets with that mount.

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#4 Der_Pit

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Posted 19 September 2019 - 07:52 AM

Have you played with the aggressiveness settings?  Zig-Zag curves usually suggest too rigid corrections, lowering it might help.

If it really is the mount that can 'just' be tamed, lower the exposure time and make sure you use subframe readout.  A too long delay between measurement (exposure) and application of the correction can enhance small intrinsic oscillations....



#5 nateman_doo

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Posted 19 September 2019 - 10:39 AM

If you are using the 8" RC and the QHY174 camera then you have something wrong with your configuration in PHD. Some quick math shows your reported image scale at around 3 arc seconds per pixel which is way off what it should be. The camera has 5.86 micron pixels and the focal length is 1600 mm. So, un-binned the guider image scale is .76 arc seconds. You'd have to bin it way up to get the numbers that you are showing. In turn that makes the RA guiding much better. On the other hand, perhaps on this night you were not using the OAG.  Then, I'd wager that with a guide scope this is as good as it gets with that mount.

Rgrds-Ross

Apologies, ED 102 (700mm focal length)  And its the QHY 163C, but the camera being used for the OAG is the ASI 174mini



#6 nateman_doo

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Posted 19 September 2019 - 10:43 AM

Have you played with the aggressiveness settings?  Zig-Zag curves usually suggest too rigid corrections, lowering it might help.

If it really is the mount that can 'just' be tamed, lower the exposure time and make sure you use subframe readout.  A too long delay between measurement (exposure) and application of the correction can enhance small intrinsic oscillations....

I will turn the RA aggressiveness down to 50 from the default of 70.


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#7 View2

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Posted 19 September 2019 - 10:43 AM

Try the RA aggressive setting? Also the hysterisis function can smooth things out. Personally my aggression usually works best around 80

Edited by View2, 19 September 2019 - 10:44 AM.


#8 rgsalinger

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Posted 19 September 2019 - 11:27 AM

Thanks. The other thing to try is to increase the exposure time to more like 4 seconds. I've not used PHD for a while but what I do is to use a delay between exposures and then short actual exposures. That way bright guide stars are not saturating but the guiding cadence is not less than 3 seconds ever. I would not increase aggressiveness because that will make each correction larger. Having said that, I do think that the hysteresis setting might improve things. As always, if the stars are round, then stop fiddling wink.gif and be happy.

Rgrds-Ross



#9 Mert

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Posted 21 September 2019 - 06:54 AM

The comment of Grit in the RA-worm-wormwheel sounds familiar

to me.

Likely I will dismantle my EQ6 and clean the thing out again with

an Ultrasonic cleaner and regrease. ( must have been > 5 years

since the last time I did thatblush.gif  )




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