Recalibration of guiding routine with ASIAIR Plus - how often?

[Steve143]

Hi all,

I'm currently autoguiding with the Plus and noticed last night that my guiding wasn't as good as previous sessions. It could be that my mount needs a bit of TLC as the guiding got worse when I was shooting near the zenith. Once I did the meridian flip it seemed to improve and then I went for another target lower in the sky and the guiding was better. Should I be running the calibration routine before every session or can a single calibration be used for multiple sessions? I usually don't break down my set up after a session as I normally just lift the whole thing in and out of the house whenever I get some clear skies, which isn't often at the moment. 

Thanks for any advice on running the guiding calibration routine in the ASIAIR app. 

Steve 

[scotty38]

If you're moving the rig then I assume you will do a new polar align when you set back up and so, in theory, should also recalibrate too

[Ouroboros]

I polar align every time I set up - that’s a given. I then re-calibrate every time I image a fresh target and after doing a meridian flip. Recalibration is so quick and easy to do on the ASIair it doesn’t seem worth starting an imaging session only to find it’s not guiding  very well. But what I’m doing may not be strictly necessary. 

I do notice that guiding performance varies between different sessions. That is often reflected in the amount of time it takes for the guiding to recover after dithering. Rightly or wrongly I have put that down to how well my mount is balanced. As with my previous skywatcher mount, it’s so stiff that finding the right balance point is a matter of guess work. If the dither recovery is too bad I stop imaging and shift the counter weight either way a few centimetres until I find guiding performance improves.  

[Steve143]

1 hour ago, scotty38 said:

If you're moving the rig then I assume you will do a new polar align when you set back up and so, in theory, should also recalibrate too

Yes, I always run the polar alignment routine before every session, check focus and then start guiding once on target. 

Edited November 29, 2022 by Steve143

[Steve143]

31 minutes ago, Ouroboros said:

As with my previous skywatcher mount, it’s so stiff that finding the right balance point is a matter of guess work.

My EQM-35 is stiff too so I'm hoping the balance is correct. There is also some minor backlash in both RA and DEC so it would probably improve if I could remove that.  

[scotty38]

49 minutes ago, Steve143 said:

Yes, I always run the polar alignment routine before every session, check focus and then start guiding once on target. 

Ok, well moving the rig means you should recalibrate and also, even if the rig did not move, a new Polar Align should necessitate recalibration too.

[Steve143]

18 minutes ago, scotty38 said:

Ok, well moving the rig means you should recalibrate and also, even if the rig did not move, a new Polar Align should necessitate recalibration too.

Thanks. I'll run a new calibration next time I'm out and see if that makes a difference. 

[Elp]

I think you need to do it if you're going to be changing targets or moving somewhere different in the sky. If you think about it, if you're pointing near the zenith the star field will hardly appear to move, if you point near the celestial equator the stars will appear to move a lot more. Unless the calibration accounts for this you'd have to recalibrate, or at least try adjusting the sidereal rate. To be safe I recalibrate every session on each target.

[The Lazy Astronomer]

1 hour ago, Elp said:

I think you need to do it if you're going to be changing targets or moving somewhere different in the sky. If you think about it, if you're pointing near the zenith the star field will hardly appear to move, if you point near the celestial equator the stars will appear to move a lot more. Unless the calibration accounts for this you'd have to recalibrate, or at least try adjusting the sidereal rate. To be safe I recalibrate every session on each target.

As per the phd instructions (https://openphdguiding.org/man-dev/Basic_use.htm#Automatic_Calibration) 

Because this is a measurement process that is subject to various kinds of mount and atmospheric effects, the most accurate results will be gotten when the scope is pointing within 20 degrees of Dec = 0 (near the celestial equator) and at least 60 degrees above the nearest east/west horizon (i.e. within 2 hours of the celestial meridian).  Calibrations can be done in other pointing positions if required by conditions at your site but they will be subject to somewhat more measurement uncertainty.  You cannot do calibrations pointing very close to the north or south celestial poles, and the mount must be tracking at the sidereal rate.

Edited November 29, 2022 by The Lazy Astronomer

[Steve143]

Thanks everyone for your advice and comments. I'll look to recalibrate for each session to make sure the guiding is as optimal as possible.  

[Phillyo]

I rarely do a re-calibration. Unless the orthogonal angle has changed, or unless I've moved my mount then there's no point. It doesn't matter where you're pointing in the sky, once you have a good calibration it won't change (except for orthogonal or mount position change).

Guiding varies night to night. Sometimes around 0.5"RMS, sometimes closer to 1"RMS. The seeing is a larger determining factor for me.