Hello 
i ve just started this hobby a few months ago and  i m using EKOS since , A nice piece of work !

i ve got a question on polar alignement.  
in my workflow , i first align with my polar scope then i launch Ekos and made a polar alignment with my main imaging camera (ZWO 533) and my scope (600mm).  The error before the ekos polar alignent is roughfly 2 or 3 minute arc and after ekos aligment procedure i v got around 20sec error , depends if it is before a beer or after. 
I start imaging, guiding without too much problem (except guiding after meridian flip)

At the end of the night , i make a polar alignment measure to check , and each time i m ending with 5 to 8 minute arc error . 

i ve double check the leveling of the mount (EQM35-pro, not on a fix pier),
The alignment of the imaging scope on RA axis doesnt seem too bad and with the ekos procedure it is not a problem if i understand . 

do you have any idea of what i missing? 

Is doing alignement with a 600mm scope is too much ?   when correcting error , it is so sensitve when turning the alt-azm knobs 


thanks

florent
 

Hello, and welcome to the forum.

As you are not using a pier, there are more variables at play. As the scope moves throughout a session, the weight is distributed to different legs of the tripod. You did not mention if your tripod is sitting on ground, pavement, or concrete, but if not a solid substrate, packing can occur as the weight shifts. Tripod leg clamps are also subject to some play, as are the joints in the legs and attachment points from the mount to the tripod. Each of these things by themselves may not be very large, but if you add them up, an arc-minute or two of change is not unexpected. If the night is breezy, that adds to it as well.

What I would say is, if it is not affecting your imaging, I would not worry about that small of a change over a night's time.

Jim

Hi
thanks for your response ,
My mount is on concrete and it is not so windy

At first i suspect the cats running into the tripod but one night i kept them inside house , same thing

I think you are right and during the night the differents slew must move a little bit the tripod . it is so sensible when i making polar alignement
i m going to slew slower may be it will help

As i m struggling with autoguiding calibration , i m looking to check every aspect. i know my mount is not very well tuned and on low end for astrophotography

an other thing, when i m doing polar aligment with ekos i m using my main scope/cam , 600mm.
yesterday at the beginning of imaging i was around 20sec arc polar error
at the end , i was around 5minutes.
I check the polar error using my guide scope , 162mm/ZWO120mm mini , and the error was around 1,5min

Why ekos mesure different polar error when using different focal lenght ?
is doing polar alignement with 600mm is not a good idea ?

thanks

Something you could try would be to align again right away after the first alignment, and see how large the error is that is reported. Make sure you start it from the same position as the first time as well. As mentioned, there any many things at play. Even some droop in the camera or focuser that changes with position of the tube can add to the error.

Maybe flex in the optical train? Focusser?