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Helical focuser as fine tuner on Astroscan?

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#1 Tom Cunningham

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Posted 26 February 2021 - 04:25 PM

OK, don't laugh, but is it even feasible to drop a helical focuser into an Astroscan drawtube to smooth out the otherwise somewhat jerky stock focusing?  I've tried larger knobs but that doesn't quite cut it.  I realize I'll be adding a couple inches of extension which may be too much, but that's why I'm posting this in beginners, I haven't a clue.  BTW, I don't really want to cut into the scope or otherwise alter it, this is just an "I wonder" project.  Also, I do have a better scope, a Sky Watcher Evostar 80ED, so no worries there. laugh.gif



#2 jeffreym

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Posted 26 February 2021 - 05:30 PM

Good question.  I don't think anyone has probably tried that.  However, if you (or anyone here) use the distance provided in this image you can test the thought without actually having the focuser.  Rack the focuser all the way in, then rack it out 1/4".  Point the Astroscan at a good star field and hold an eyepiece about the distance approximate to where it would be held in the HF.  Estimate the midpoint of the HF range. you might be able to simulate this by using an inexpensive barlow, just remove the barlow lens from the unit so it's just a spacer.  The unit in the picture has 1cm of focus travel.

 

Not counting the silver 1.25" barrel section, the HF is Minimum length: 43mm - Longest length: 53mm

 

My son has my Astroscan or I would try it myself.

 

Post what you find.

 

Have fun,

Jeff

Attached Thumbnails

  • Helical Focuser crop sm.png

Edited by jeffreym, 26 February 2021 - 05:40 PM.


#3 izar187

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Posted 27 February 2021 - 07:54 PM

I do not _know_ first hand, but I suspect weight could be an issue, with a helical add in.
'Scan sold early on with some of the lightest ever production ep's, not by coincidence.
During dew/frost, any heavy combo in the focused could cause balance problems.
IME

#4 davidmcgo

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Posted 28 February 2021 - 12:54 PM

The best trick with an Astroscan focuser is the get a roll of thin Teflon adhesive tape and put a small strip on the rail opposite the roller and a little up and over the lip of the focuser body.  Really smooths it out.  Also if you adjust the little spring notches you can rotate the eyepiece a bit while putting in or out a bit to fine tune, assuming the eyepiece doesn’t have undercuts.

 

There won’t be enough travel for those helical focusers.

 

Here is a link to the type of tape I used on mine.

 

https://www.mcmaster...Box=teflon tape

 

Dave


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#5 Tom Cunningham

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Posted 02 March 2021 - 11:48 AM

There won’t be enough travel for those helical focusers.

Thanks for the tip, Dave!  Are you talking inward travel or outward travel?  Also, would the tube slip with the teflon tape if any extra weight was applied?



#6 davidmcgo

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Posted 02 March 2021 - 09:30 PM

The helical focuser would not let you get the eyepiece in far enough.  The scope isn’t suited for heavy eyepieces but haven’t had any slipping with normal Plossls or orthos

 

Dave


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