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Tuning up the stock focuser

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#1 jmer1234

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Posted 12 January 2018 - 03:11 PM

I have purchased my first telescope, a Meade Polaris 130, after lurking on this site for a number of years. I had a few sessions practicing setting it up and finding objects in the night sky with it, while I waited for a collimation eyepiece I ordered to show up. When it finally arrived, I started working on checking the collimation and was horrified as I realized how much the stock focuser rocked back and forth as it ran through its full travel.

 

Are there tips I can employ to tune up the stock focuser to help steady the tube as it travels? Are there any upgrade focusers that could be recommended for a 5" newtonian? The only focusers I have been able to find are for 6" tubes and greater.



#2 Jon Isaacs

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Posted 13 January 2018 - 03:18 AM

Jmer:

 

Hello and welcome.gif to Cloudy nights. 

 

I am not familiar with the Polaris focuser,  is it plastic?  Photos of the focuser top and bottom would be helpful. 

 

Many focusers have two small recessed screws opposite the focuser shaft that can adjust the slop in the tube.  Removing the pinion staft,  removing the drawtube and cleaning the thick grease and then reassembling it and adjusting it can make a big improvement.  If there are no adjustments,  it can be shimmed. 

 

As far as a replacement focuser, small washers between the focuser and the tube can be used to make a focuser meant for 6 inch scope fit a 5 inch. 

 

https://agenaastro.c...ngle-speed.html

 

Jon



#3 jmer1234

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Posted 14 January 2018 - 09:07 AM

Thanks for the response, Jon Isaacs. The focuser is plastic, and I don't see any screws like you mention; just the pinion cover screws. I may try shimming next. Are there any suggestions for what works best as a shim?

 

I have looked at that focuser, and may consider it if I really find the wiggle to be a problem. But, in reality, for a cheap, beginner scope, I may hold off on that upgrade until I get a more substantial telescope.

 

gallery_222543_8758_2173658.jpg

Edited by jmer1234, 14 January 2018 - 09:16 AM.


#4 Jon Isaacs

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Posted 14 January 2018 - 10:47 AM

Jmer:

 

If there are screws,  they'd be in the part of the focuser not visible in your photo,  same view but taken from the other side. 

 

Cleaning and "de-gooing" will make it easier to turn. 

 

As far as a shim,  a thin piece of Teflon is ideal but you probably don't have any.  Any sort of slick plastic should work.  It has the be the right thickness.  I'd just experiment.  A milk jug is probably too thick.  It needs to be reasonably strong. 

 

What I've done in the past is cut a strip of the plastic about 3/4"-1" wide by maybe 4 inches long.  

 

I try to slip it between the drawtube and the body on the side opposite the pinion shaft,  the side not visible in the photo.  I try to slip enough in so it covers the length of the focuser body. 

 

To secure it,  I bend the remaining plastic over so it lies along the outside of the focuser body and put a couple of wraps of tapes around the focuser body , taping the plastic down against the body. 

 

Hopefully my directions make sense,  otherwise I'll try to take a photo or two. 

 

Jon



#5 MrJones

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Posted 14 January 2018 - 11:03 AM

"horrified as I realized how much the stock focuser rocked back and forth as it ran through its full travel"

 

I had a similar problem with my Meade 102mm Infinity focuser. After going through other focuser improvement articles and threads and shimming not improving much, I managed to get mine working pretty well by putting 2 felt furniture pads (1/2" round) in the focuser housing to support the drawtube. I should have taken a photo but maybe the description can help.



#6 jmer1234

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Posted 17 January 2018 - 07:28 AM

Thanks for the responses, everybody.

 

I may try the felt pad option, MrJones. Depending on how thick it is, it may also help with the fact that accidentally bumping the eyepiece with my head/brow will change the focus.  

 

The focuser already has a piece of plastic tape of some kind, opposite the pinion shaft, so if I use teflon tape, or pieces of plastic, they will probably be on the sides (the direction of the rocking).



#7 JohnnyBGood

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Posted 05 February 2018 - 12:25 PM

I have the same scope and love it. The focuser came with the plastic strip of tape at the 12:00 position so I added some very thin felt strips at the 4:00 and 8:00 positions and lubed the felt and focuser tube with some white lithium grease and that solved the problem. If the felt is too thick the focuser becomes stiff and difficult to turn, so it may take some trial and error getting it the way you want it. With some felt you can sort of peel off layers to make it thinner.

 

After that I didn't have trouble with slop in the focuser anymore, but focus at high power was still touchy since the "sweet spot" is so small. I'm in the process of figuring out how to add a helical microfocuser to make that easier, and while I've managed to jury rig it into functioning (it's soooooo much nicer to use now) I'm still figuring out how to optimize it.




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