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Old 12-05-2022, 07:06 PM
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Drac0 (Mark)
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"Acceptable" backlash - AZ-EQ5

Just wondering what would be considered as acceptable DEC backlash for my new mount? Out of the box PHD2 measured a little over 1000ms, I gave it a very slight tweak and it's down to ~750ms. Another little tweak today but can't test it until the skies clear for a few hours.

Is it worth trying to get it down any further, especially with nice round stars in 5 minute subs?

Cheers,
Mark
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Old 12-05-2022, 08:10 PM
Startrek (Martin)
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Mark,
I’ve spent hours and hours on both my EQ6-R mounts re balancing, minimising Dec and Ra backlash via the worm drive carrier and the drive motor belts and the lowest I can get down to according to the PHD2,Guiding Assistant is around 900ms
However this figure changes in different parts of the sky and under varying Sky conditions.
I wouldn’t pay too much attention to the backlash figures in the GA ( unless they are quite high + 2000ms ) I tend to analyse my guiding error numbers over a nights imaging from night to night
2 weeks ago on Thursday night my guiding was 1.25 to 1.50 arc sec see sawing all over the place ( obviously chasing the seeing ) pretty bad , then the next night 0.60 to 0.70 arc sec and really tight and stable. Conditions can change so much.
Since 2020 , I’ve changed from the Hysterisis algorithm to the predictive periodic error correction PPEC in PHD2 and found without any doubt that my overall guiding is not so much tighter, maybe slightly tighter ( as this is mostly dependent on prevailing conditions ) but more stable over a session.
Tuning and rebalancing my mounts has improved guiding by at least 20%
A backlash figure of 750ms is fine for your mount
At the end of the day the proof in the pudding is your images and whether your stars are nice and round and tight
One thing I’ve found again and again small tight stars are a result of excellent seeing and therefore good tight guiding
Bloated or fatter stars , but still round are a result of poor seeing and therefore poor guiding ( see sawing )
If your getting nice round tight stars with 5 min subs , don’t fiddle with your mount, I think it’s telling you I’m Ok.
Cheers
Martin
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Old 13-05-2022, 11:38 AM
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Drac0 (Mark)
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Thanks Martin.
Not really concerned about it, was quite happy with guiding even in the wind last week. Was just wondering if it was worth the effort to look for 'better' results. Will leave it as is at least for now.

Cheers,
Mark
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Old 13-05-2022, 05:40 PM
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The_bluester (Paul)
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My attitude is that as long as your guiding program can correct for the backlash reliably without either sending itself into oscillations or taking too long to get the mount moving when the direction of guiding reverses, why spend the time?

But I am also a tech at heart, "Because I want to" is a valid answer to that question.
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Old 13-05-2022, 07:13 PM
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AstroJunk (Jonathan)
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And ensure the scope is out of balance! The worm screw needs to rest with some, but not kg's of weight against the worm gear to ensure minimal backlash. If the balance is perfect, then you can get rocking in the ota as it compensates too and fro.
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Old 13-05-2022, 10:27 PM
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Drac0 (Mark)
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I have to wonder how long I can keep my hands off it "Because I want to"
Quote:
Originally Posted by The_bluester View Post
My attitude is that as long as your guiding program can correct for the backlash reliably without either sending itself into oscillations or taking too long to get the mount moving when the direction of guiding reverses, why spend the time?

But I am also a tech at heart, "Because I want to" is a valid answer to that question.
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