what to do about hysteresis and flexure

[prefetch]

so the other night i ran a hysteresis test using sequence 0.2.0.3 and found what i suspected - my setup is not the most stable.

 

flexure error: 33.3 arcseconds

hysteresis error: 52.9 arcseconds

 

these seem kind of bad.  mounting my gear onto my permanent observatory is a step in the right direction, but in the interim i have to deal with a tripod resting on a rolling platform (with wheel locks.)

 

just curious what other people are getting for their measurements, how they are mounted and what solutions people have used.

[LucMurphy]

The hysterisis will affect the pointing accuracy while the flex will affect your MLPT performance. Both error cannot be modeled.

I saw hysterisis error from 30 arc sec to 60 arc sec (DDM60 + Celestron 11in.) depending on the season (I get from +20 degC to -20degC). Personnaly, i can live with a pointing error of a few minutes. Not great but it is workable.
I was initially getting a time flex error of 10 arc sec / 20 min. that is definititely not good for long un-guided exposure. After a 6 months investigation, my time flex when down to less than 2 arc sec / 20 min!

That's one of the beauty of this mount/sotfware: you have tools to do a diagnosis of the mount performance...

Regards

Luc

[prefetch]

yeah, i guess pointing accuracy isn't that big of a deal.  i wasn't aware that hysteresis only effected pointing.

 

so could you explain more about how you got your flex time down to less than 2 arcsecs??  that's sounds really awesome.

[LucMurphy]

hysterisis also affects MLPT but it is partially "removed" when the MLTP run starts. So, in my experience with my setup, time flex is sometime I needed to control more closely than hysterisis. Other may have other experiences.

 

To make a long story short (remember, it took me 6 months of trials and errors to fix the problem), I made my setup more rigid by adding a second dovetail on top of the C11, made my rotable focuser non-rotable, added provisions to prevent main mirror flop and other minor stuff. All that allow the flex to go down to about 5-6 arc sec / 20 min. And then, it started to creep up again! I did noticed this time however that the power cable of my FLI camera was getting very stiff when temperature was sub-zero (I have the non-pro DDM60). I re-arrange the cables (for the 4th time), and I finally got a descent time flex 1.6 arc sec /19 min. I made a couple more flex measure and they all had similar results of less than 2 arc sec / 20 min.

 

Regards

Luc