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Image Shift with new micro pinion on older Tak FC100

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#1 amys

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Posted 16 March 2020 - 12:54 PM

I hope someone has a solution to this problem.  I bought a beautiful older Tak FC100 several weeks ago and wasn't terribly happy with the stiff single speed focuser.  So I ordered the Starlight Instruments 2.7" micro pinion focuser.  It's really beautifully made but I'm having an annoying issue.  When I adjust focus, there is significant image shift.  I've tried tightening it down with the two Philips screws and I'm pretty sure the leveling screws are adjusted properly.  I don't recall any image shift was using the original focuser but I only tried it out once before installing the micro pinion.  Any thoughts on how I can eliminate the image shift?  I'd really like to be able to continue using it because having the fine focus is such an improvement.

 

Thanks



#2 Kunama

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Posted 16 March 2020 - 02:05 PM

Amy, image shift happens with Tak focusers if the draw tube glide strip pressure is either insufficient or uneven.

Along the top of Tak focusers there are small set screws in front and behind the lock knob. These are covered with a lacquer to stop them moving unintentionally. 

To adjust the glide strip pressure you remove the pinion assembly, then soften the lacquer with a drop of nail varnish remover (acetone) then using an Allen key tighten these set screws so that the drawtube moves smoothly but without any sideways play through its full travel distance.

Once that is done you can reinstall the micro pinion assembly.....

 

From memory the required Allen hex key is 1.3mm.  You can buy a cheap set of mini Allen keys of 0.9mm to 2.5mm at hardware stores or electronics stores.


Edited by Kunama, 16 March 2020 - 02:11 PM.

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#3 amys

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Posted 17 March 2020 - 08:27 AM

Thanks very much for posting this suggestion.  I will examine the scope today and see if I can find the two screws.  I'm not sure what you mean by gide strip pressure.  I do notice that the rack position seems to change when I pull the draw tube out.  I'll try to post some photos to get an opinion as to whether this is what's causing the shift.  I don't recall seeing any image shift before I installed the micro pinion but I only used it once.



#4 Jon Isaacs

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Posted 17 March 2020 - 09:53 AM

Amy:

 

If you haven't called Starlight Instruments, I recommend doing that.  They are very knowledgeable and very helpful.  

 

Jon


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#5 Carl N

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Posted 17 March 2020 - 10:18 AM

Also, SI has a pdf on their website for the take focuser setup adjustments. After your adding the SI parts you will definitely need to check the adjustments of the leveling screws not just the Phillip's attachment screws.

#6 amys

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Posted 17 March 2020 - 11:58 AM

Yes, I've been in communication with Wayne at Starlight Instruments and I've been working on adjusting the leveling screws.  Will post those photos of the rack later today.  Thanks


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#7 amys

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Posted 17 March 2020 - 12:50 PM

I removed the micro pinion and watched the rack as I pulled out and pushed in the draw tube.  There does not seem to be any wobble as it moves in and at and no side to side movement of the rack as I move the draw tube in and out.  Before fiddling with those 2 adjustment screws in front of and behind the brake, I decided to reinstall the original parts to see if there is any image shift.  I might be able to try it out tonight and will post back.


Edited by amys, 17 March 2020 - 12:51 PM.


#8 Kunama

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Posted 17 March 2020 - 05:21 PM

The reason you get image shift is that the teeth on the rack and on the pinion are angled so there is a tendency for some unwanted lateral movement with the desired longitudinal movements.

 

Takahashi focusers like many others have Teflon glide strips, the difference being that on Taks there is access to the set screws to apply pressure to the glide strips and thereby to the draw tube.

 

The two screws that put pressure on the pinion should not be used to try to do the job of those set screws pressing on the glide strip. The pinion pressure screws are used to set the ideal meshing to control backlash.

 

I have done these adjustments to fine tune many of my 19 Takahashi scopes, I have also had at least 10 FT micro pinion assemblies.


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#9 amys

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Posted 17 March 2020 - 07:29 PM

I think I get what you’re saying.  Just tighten the 2 screws over the pinion enough to prevent backlash and tighten the 2 screws near the brake to adjust tension.  I’ll see how it works with the original parts and then try again with the micro pinion.  Thanks again for your help. 



#10 Kunama

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Posted 17 March 2020 - 09:38 PM

I think I get what you’re saying.  Just tighten the 2 screws over the pinion enough to prevent backlash and tighten the 2 screws near the brake to adjust tension.  I’ll see how it works with the original parts and then try again with the micro pinion.  Thanks again for your help. 

 

Just remember that the rack&pinion backlash adjustment is done after the drawtube glide pressure.


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#11 amys

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Posted 18 March 2020 - 06:29 AM

Got it. Will work on it today.

#12 Ihtegla Sar

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Posted 18 March 2020 - 09:37 AM

Amy:

If you haven't called Starlight Instruments, I recommend doing that. They are very knowledgeable and very helpful.

Jon


I will second Jon's suggestion. I recently had the need to call Starlight on two different matters and both times they were very friendly and helpful. Starlight has excellent customer service.

#13 Carl N

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Posted 18 March 2020 - 10:07 AM

I will second Jon's suggestion. I recently had the need to call Starlight on two different matters and both times they were very friendly and helpful. Starlight has excellent customer service.


Wayne is a gem and role model of small business

#14 amys

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Posted 18 March 2020 - 10:16 AM

Yes, Wayne has been very responsive.

#15 amys

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Posted 19 March 2020 - 06:57 PM

Amy, image shift happens with Tak focusers if the draw tube glide strip pressure is either insufficient or uneven.

Along the top of Tak focusers there are small set screws in front and behind the lock knob. These are covered with a lacquer to stop them moving unintentionally. 

To adjust the glide strip pressure you remove the pinion assembly, then soften the lacquer with a drop of nail varnish remover (acetone) then using an Allen key tighten these set screws so that the drawtube moves smoothly but without any sideways play through its full travel distance.

Once that is done you can reinstall the micro pinion assembly.....

 

From memory the required Allen hex key is 1.3mm.  You can buy a cheap set of mini Allen keys of 0.9mm to 2.5mm at hardware stores or electronics stores.

Matt:

 

I was able to adjust the glide pressure using the screw in front of the brake.  The set screw behind the brake wasn't moving and I didn't want to force it.  The movement of the draw tube seems smooth and I don't feel or see any sideways play but how do I know how much pressure is enough to prevent image shift?  Just trial and error?  I've made the adjustment with the original focuser parts reinstalled and should be able to try it out on Saturday.  If I don't see any image shift, will reinstalling the micro pinion affect that?  Will I have to readjust that set screw? 

 

Sorry for these bonehead questions.



#16 Scott in NC

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Posted 19 March 2020 - 07:43 PM

Amy, just like you, I've noticed a tiny amount of image shift from my FS-102's focuser after adding the FT MPA.  I had never noticed that issue with the stock focuser alone.  The degree of image shift has never been enough for me to want to make any further adjustments, but at some point I'll probably try the recommendations above.  So thanks for posting your question!



#17 Kunama

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Posted 19 March 2020 - 08:01 PM

Matt:

 

I was able to adjust the glide pressure using the screw in front of the brake.  The set screw behind the brake wasn't moving and I didn't want to force it.  The movement of the draw tube seems smooth and I don't feel or see any sideways play but how do I know how much pressure is enough to prevent image shift?  Just trial and error?  I've made the adjustment with the original focuser parts reinstalled and should be able to try it out on Saturday.  If I don't see any image shift, will reinstalling the micro pinion affect that?  Will I have to readjust that set screw? 

 

Sorry for these bonehead questions.

Amy, the MPA installation should not induce any change.  Install the MPA, setting for minimal backlash without binding.

It means getting the two ‘pull’ screws and the 4 ‘push’ set screws tightened so that the MPA to focuser gap is even all round and the backlash disappears but not too much pressure is transferred onto the pinion.... might take a few goes to get it perfect..


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#18 amys

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Posted 20 March 2020 - 07:08 PM

Ok.  I reinstalled the micro pinion after adjusting the glide pressure.  It feels pretty good as I rack the focuser in and out except for the backlash.  Wayne had told me to tighten the screw on the collar to reduce backlash.  I've tightened it as much as I feel I should because the instructions say not to over-tightened.  There just seems to be too much slack when I reverse direction.  Suggestions?

 

Thanks again.


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#19 Kunama

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Posted 20 March 2020 - 09:53 PM

Ok.  I reinstalled the micro pinion after adjusting the glide pressure.  It feels pretty good as I rack the focuser in and out except for the backlash.  Wayne had told me to tighten the screw on the collar to reduce backlash.  I've tightened it as much as I feel I should because the instructions say not to over-tightened.  There just seems to be too much slack when I reverse direction.  Suggestions?

 

Thanks again.

Using the Allen keys that came with the MPA turn each of the four corner set screws on the MPA counterclockwise 1/8 turn and tighten the two pull screws slightly, then test backlash.... if needed, repeat till the feel is right.

 

P.S.  they would only be ‘bonehead’ questions if you thought them but didn’t ask them.... flowerred.gif


Edited by Kunama, 20 March 2020 - 09:57 PM.


#20 rkelley8493

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Posted 21 March 2020 - 01:14 AM

I had to return the 2.7-MPA and exchange it for the 2.5 because I was having similar issues. I mistakingly ordered the 2.7 because the specs listed the Tak-100DF as having a 2.7" focuser. However, the 2.7-MPA was just a bit too large for the focuser to move smoothly. You can see in these photos that the 2.5 was a better fit, and it has been working very well since I installed it. Wayne was pretty helpful throughout the whole process. The exchange only took a few days.

Forgot to mention, Wayne also helped me with outfitting the MPA with a silver fine focus knob. It looks really good on the FC-100  laugh.gif

 

MPA 2.7 :

 

mpa2.7 2.jpg

mpa2.7 (1).jpg

mpa2.7 3.jpg


Edited by rkelley8493, 21 March 2020 - 01:26 AM.

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#21 rkelley8493

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Posted 21 March 2020 - 01:16 AM

MPA 2.5 :

 

feather 2.5.jpg

feather. 2.5.jpg

feather.2.5.jpg


Edited by rkelley8493, 21 March 2020 - 01:21 AM.

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#22 amys

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Posted 21 March 2020 - 05:12 AM

Using the Allen keys that came with the MPA turn each of the four corner set screws on the MPA counterclockwise 1/8 turn and tighten the two pull screws slightly, then test backlash.... if needed, repeat till the feel is right.

 

P.S.  they would only be ‘bonehead’ questions if you thought them but didn’t ask them.... flowerred.gif

bow.gif yes, I’ve been adjusting the 4 push screws and 2 pull screws but can’t eliminate the backlash.  The instructions do say that there should be a small amount of backlash and if the image shift is gone, I’ll not complain.  I guess I’m just not clear about what I’m aiming for when adjusting the screws other than leveling, which is not easy to see on the back side.  I should be able to test it tonight if the wind dies down. 



#23 amys

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Posted 21 March 2020 - 05:14 AM

Thanks for posting those photos.  My Tak is from the mid-90’s and the 2.7” is supposed to be the right one.  Wayne asked the same question.  The fit looks perfect.


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#24 rkelley8493

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Posted 21 March 2020 - 01:03 PM

Thanks for posting those photos.  My Tak is from the mid-90’s and the 2.7” is supposed to be the right one.  Wayne asked the same question.  The fit looks perfect.

Oh, I gotcha! My mistake smile.gif I haven't had any experience with those. Matt [Kunama] knows what he's talking about waytogo.gif



#25 amys

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Posted 21 March 2020 - 02:44 PM

I did a little more fiddling today.  I removed the micro pinion and loosened the screw on the collar, which I thought I had over tightened yesterday.  When I reinstalled the micro pinion, I adjusted the 4 leveling screws so they just touched the scope and then tightened down the 2 "pull" screws.  Those adjustments eliminated the backlash.  smile.gif So tonight I will find out if this had all improved the image shift.  fingerscrossed.gif Will report back.

 

Thanks again.
 


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