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N.I.N.A. and autofocus after meridian flip

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#1 fmazzanti

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Posted 24 January 2022 - 03:20 AM

Hi folks,

 

I'm a beginner N.I.N.A. user who is anyway enjoying it a lot, using it with my TEC140 on a Paramount MX mount.
Everything works nicely but I have found a weird behaviour... I have it configured in the (simple) sequencer so as to autofocus right after meridian cross, and that systematically fails for no apparent reason :(
I'm using an Optec FocusLynx with a Handy Stepper motor on the TEC140. This has been working very well for the last years without problems.
In my regular workflow I start imaging an object that is about 30 to 40 degrees high East, so that I can take advantage of almost all night imaging it. When the object is East of the meridian, I can successfuly autofocus every 5 images or so, no problem. But when the meridian flip occurs, it can not focus anymore, it says:

 

"Error: determined focus point position is outside of the overall measurement points of the curve. Fitting is incorrect and autofocus settings most likely incorrect."

 

Now the statement is clear about my settings, though I followed this link to adjust them

 

https://www.youtube....h?v=lHrfaR7A0L0

 

and systematically get an R^2 value of 0.98 or 0.99 when I try to autofocus East of the meridian (not in a sequence, but testing it).

What could be the cause for that? DO you have any suggestion here about what parameters to change?
 

Thanks a lot in advance,

 

Ferran.



#2 happylimpet

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Posted 24 January 2022 - 06:26 AM

What does the autofocus curve look like, and is it finding plenty of stars in the focus frames? I think you really need to watch it focusing to find out whats wrong.



#3 fmazzanti

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Posted 24 January 2022 - 08:31 AM

Hi,
it just looks like a nice V-shaped curve when I llok at it before meridian flip. After the flip I don't know, I'll have to check.
But once again, if it works well Eaat, why not after meridian flip?
What can be going wrong here?
Beat,
Ferran

#4 unimatrix0

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Posted 24 January 2022 - 10:56 AM

There are many possibilities 
Did you give enough time for the mount settle?  I had given short time before (4-5 seconds) and turned out the mount was still in motion when it tried to plate solve and/or do an autofocus routine. 

Your mount is set up somehow incorrectly , maybe the local coordinate is put in wrong (happened to me) and the telescope maybe pointing to the ground or an object , because it slewed to the wrong location? 

 

Your focuser unable to turn in/out the focuser tube  (ie: cable snag), or the focuser tube has a lot of play and slips , which only gets more apparent after the telescope is in a different position? 
Change in temperature (colder) the focuser got sluggish/and or the focuser isn't receiving enough voltage and it's not turning enough on the focuser rotor and not making enough difference between focusing points? 


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#5 Dean

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Posted 24 January 2022 - 11:18 AM

My guess would be the focuser slipped significantly during the flip somehow.

 

The FocusLynx attaches to the TEC140's focuser shaft with a tiny 1/16" allen screw - maybe check that is tight enough as well as the screw that tightens onto the focuser housing. Also make sure the FocusLynx motor cover is turned enough that the motor is fully engaged.

 

I have the same combo (FocusLynx on a TEC140) and found that it's pretty picky about how well the manual knob is centered in the housing. If it doesn't have the correct centering, the focuser motor will stall and totally mess up any autofocusing. I had a problem where the motor would stall with the scope pointed in one direction but not when pointed in another. Near as I could tell that was because the motor had to exert more torque in some orientations which caused more flex and binding. After carefully adjusting the centering and making sure both screws were tight the problem went away. I'm not sure this is your problem as I would have expected you to have seen the problem before.


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