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Image Shift with new micro pinion on older Tak FC100

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#26 amys

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Posted 21 March 2020 - 07:08 PM

Well, it didn't go as well as I had hoped but this is what I'm seeing.  With the scope pointed nearly south at Sirius, the star would shift to the west when I initially racked the focuser in a little.  But if I continued to rack it in, it didn't shift anymore.  Similarly, when I turned the fine focus knob in the other direction, the star would move to the east when I changed direction but would then stay put if I continued to rack the focuser out.  Is this a backlash issue?  



#27 Kunama

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Posted 22 March 2020 - 03:03 PM

Without seeing the focuser myself my guess is that the draw tube glide strip on top needs a little more tension.

A purely backlash issue shows up only as a small rotation of the focuser knob before the draw tube moves longitudinally when changing rotation direction of the knob.


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#28 amys

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Posted 22 March 2020 - 03:08 PM

Thanks for the feedback. I’ll continue to work on it.

#29 rkelley8493

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Posted 22 March 2020 - 10:09 PM

Try this. Mount your scope to your mount as your would if you were observing, and rotate the optical tube so the focuser is face up and parallel to the ground. This will put gravity on your side when installing the MPA. Apply pressure with your fingers [you may need to loosely tighten the set screws to hold the assembly in place], and rotate the focus knob so you can see how the rack looks when it's moving outward. You should be able to see if the rack has a "corkscrew" type of motion when it moves in and out of. Try to adjust the location of the pinion inside the MPA and/or the leveling screws until the corkscrew effect is minimal and the tension of the pinion allows the rack to move smoothly in and out of the draw tube.

This helped me with getting the MPA installed properly on a similar scope. 



#30 amys

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Posted 31 March 2020 - 02:33 PM

Update:  I was able to get out with the scope a few nights ago.  I think the image shift issue with the focuser is resolved.  I still see movement when I touch the focuser but the star goes back to center when I let go so I think this is now a stability issue rather than a focuser issue.  I found that lighter glide pressure is better so I need to find the lightest glide pressure that is sufficient to prevent drift when pointed at zenith.  Thanks very much for your help!


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#31 DeanS

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Posted 31 March 2020 - 04:35 PM

Glad you got it adjusted properly. 

 

I just installed one on my FS60C with PosiDrive and it works great.  Have been wanting to upgrade focuser on this scope for some time and Starlight finally made a micro focuser to fit this smaller scope.   Very satisfied with the performance now, particularly over the stock tak unit with robofocus.

 

Dean


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