Re: Spikes in DEC #guiding #Guiding


HI Sebastian

I suggest you take this up with AP in their forums

encoder mounts like the Mach 2 require some basic correct setup, and i'm not sure yours is there (i'm not suggesting there's anything wrong with the mount at all: you are guiding < 0.50")

 looking at a typical run, your DEC is odd for the following reasons: 
- those excursions are not the result of any PHD type of correction
- all your corrections are in one direction both RA and DEC, and corrections exhibit a clumping 

this is dec showing the large instantaneous jumps and guiding in only one direction 


I suggest you do a guiding assistant run for a few minutes to measure polar misalignment. it could be something is terribly off on polar align, but based on what you're saying i don't know. 

On Sun, May 2, 2021 at 10:29 PM Seb@stro <sebastiendore1@...> wrote:
Hi Brian,

Thanks for your reply.  Logs here:

I should probably have added that my imaging scale is 1.04"/px. So it's probably impacting a bit, maybe not much... But to be honest my concern was also about the working order the mount.  

But don't get me wrong, I'm coming from a low budget asian mount and got the Mach2 about 2 months ago. It performs WAAAAAAAAYYYYYYYYYYYYYYY better, no question there. So there's the fact that I'm not very familiar with AP mounts limits regarding tracking and guiding yet. Had a handful of clear nights only. And I know my system is the challenging kind (mirrors, long FL, reducer backfocus, etc.)... So I just thought I'd ask for educated guess here.

Might also be PA as you pointed out. But I thought I did well since I polar aligned with RAPAS at the beginning of my session and refined with PHD2 polar drift align afterward. When I ran the Guiding assistant, I recall it was saying it was around 2-3 arcmin from the NCP... Do you think it's reasonable for my imaging scale (1"/px) ?


De : <> de la part de Brian Valente <bvalente@...>
Envoyé : 3 mai 2021 00:48
À : <>
Objet : Re: [ap-gto] Spikes in DEC #guiding #guiding
Hi  Sebastien

Please upload your guidelogs for this 

Screen caps aren't enough information, but a quick glance looks like you have pretty bad polar alignment which would dramatically impact your DEC guiding

guidelogs would tell more

I wonder how much of an issue guiding is here - your overall rms is 0.49" and your image scale is 1.7"/pix, i'm guessing even if you addressed this you may not see a difference in your images


On Sun, May 2, 2021 at 9:44 PM Seb@stro <sebastiendore1@...> wrote:
Hello all, 

I'm having some spikes in my DEC guiding at times tonight. The worst ones seem to occur at periodic interval around 20-25 seconds but not all the time. Like about a dozen times in 400s periods. RMS values are good but DEC is about 40% bigger than RA because of these excursions. 

Conditions are fairly good now. No wind at all. Balance was quite accurate (as far as my eye can tell) in both RA and DEC. PA error reported by PHD2 is below 5 arc-min. I have a NUC on top of OTA, so no cable snag possible. Seeing is fair at 3.5-4".

My setup:
-EdgeHD 800 reduced to 1400mm FL
-Guide cam pixel scale : 1.7"/px
-Guiding through OAG at 3-4 seconds interval

Imaging M106 which is about 2hrs past meridian at the time of writing this.

That said, I'm not that familiar with guiding at such focal length... Any thoughts on what might be causing this ?



Brian Valente


Brian Valente

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