Jump to content


DDM RA axis going bad?

  • Please log in to reply
22 replies to this topic

#21 maxmirot



  • Beta Tester
  • 230 posts

Posted 18 October 2016 - 08:00 PM

I started using Sequence with MLPT imaging the last few nights. ( I still prefer SGP.)


However, I am getting round stars on most 20mins images using MLPT.  A recent 180 star model still shows the same pattern. Much bigger errors spread out along the RA


Everything is rock solid from the foot of the pier, focuser, scope.  The source of hysteresis is not obvious.


The increased RA error should be a clue.



#22 pesa



  • Beta Tester
  • 82 posts
  • LocationEnk√∂ping Sweden

Posted 15 November 2016 - 06:26 PM

Max, what is your mount? if it is DDM60 perhaps those are not as sturdy as DDM85?

Anyone else (then me) have same problem - rec-error much bgger then dec error? In that case, do you have DDM60 or RRM 85?


#23 maxmirot



  • Beta Tester
  • 230 posts

Posted 15 November 2016 - 09:10 PM

It is the DDM85.

It probably is hysteresis as the MLPT does make improvement it unguided error.


If you look at the JPEG I posted , the spread in the residual error  after superfit shows a non random pattern along the RA. 

I wound think this should tell us something .  I have not been able to determine a mechanical source yet.


Btw, I tried the mount with Bisque's Tpoint . I automapped about 44 points. It shows no pattern in residual error.

The pointing is no better also. 

They have a lot extra terms that autoslew does not use. None of these improve the pointing model.


There is always the possible that the pattern is an artifacts on how the autoslew does superfit.


There is so little explained with the autoslew modelling here.

We should be able to manually adjust the model by removing outliers etc and see if the fit statistics improve.

There is a lot in the advance modeling that is undocumented. I wish we knew more.


Perhaps some day Dr. Keller or ASA will spend some time on this.



0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users