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Autoguiding: 0.5x vs 1x guide rate

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#1 CyberianIce

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Posted 25 November 2022 - 06:08 AM

Why do we have theese options with PG at all? Is it vendor heritage from ST4 era? I been throuhg lot of documentation, and read every topic on this forum which is related to autoguiding. The main problem here is that I did not ended up with clear conclusion yet, but more confusion instead. The question seems simple at the first glance, binary choice: should I use 0.5x or 1x guiding rate, given that I can setup any arbitrary value on both sides (controller and guiding software). I tried to rephrase the question like this: what are pros and cons of using 0.5x over 1x and vice versa, but then got confused again, because faster guide response could be considered both as an advantage and disadvantage.


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#2 Mike7Mak

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Posted 25 November 2022 - 08:39 AM

You don't want to use a 1x guide rate because eastward correction pulses would stop the drive motor and introduce backlash problems.



#3 CyberianIce

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Posted 25 November 2022 - 10:22 AM

I understand your concern. That's exactly why i keep this mouth slightly out of balance, eastward heavy, this helps eliminate RA backlash almost entirely, but requires readjusting counterweight after MFs. Because I already have almost no backlash in RA (mount is well adjusted and belt driven), I don't think guide rates would have big impact on that. Any other thoughts?

#4 AstroVagabond

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Posted 25 November 2022 - 10:36 AM

what are pros and cons of using 0.5x over 1x 

I have no idea. I was using 0.8x and then moved to 0.5x while doing some trial and error investigation to improve guiding and found 0.5x produced the best results across several nights of testing.

 

Why that is I personally don't care because I have so many other parameters and things to understand I just left it at I'm happy I stumbled upon a change that helped improve my guiding performance on both my HEQ-5 Pro and EQ6-R Pro.

 

I do understand inquiring minds want to know, smile.gif

 

I look forward to what you determine.



#5 Mike7Mak

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Posted 25 November 2022 - 12:39 PM

Try it and see. It seems to me that at some point between .5 and 1x you're probably going to encounter overshoot and possibly escalating oscillations. Inertia and momentum. Stopping for east and pulsing the drive at twice sidereal speed for westward corrections seems rather drastic compared to simply speeding up or slowing down to keep up with guide errors.



#6 CyberianIce

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Posted 25 November 2022 - 01:18 PM

That's the line of thinking I had in mind when I told faster response may not be just better. Motors can skip steps more easily when moving from and to standstill than when slowing down or speeding up why they still have some inertia.

Also, somewhere I read that slower guide response is like natural low pass filter that can smooth the motion and that can help astrophotography, but I see no how that can help when guiding exposure already slow things down.


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