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Accessory of possible interest for refractor users

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#1 Mirzam

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Posted 15 November 2020 - 03:36 PM

I have a late-1980s AstroPhysics refractor with great optics, but a not so great focuser.  Joe LaCour of KineOptics came up with an accessory that provides a very smooth fine focus capability without requiring any modifications to the scope itself.  The accessory uses a KineOptics HC-1A focuser with a 3D-printed “snout” that plugs into a 2” diagonal.  Now I use the old focuser for rough focus and the accessory for rapid fine focus adjustment.  For those who may not be familiar with the HC (Helical Crayford) focusers, they are extremely smooth and backlash free.  Unlike the more typical threaded helical focusers, the Crayford adjusts very quickly.  I added the extra long nylon bolt to give even more leverage and feel.

 

There are a couple important considerations.  First, the focuser adds about 1 3/8” of length to the existing focuser plus diagonal.  Therefore it is essential to have at least this amount of available inward travel on the main focuser to compensate for this extra length.  You can see in my photo that there is not very much inward range left for this particular eyepiece.  Newer scopes commonly are designed to accommodate binoviewers and imaging trains, and so are likely to have plenty of inward travel range.  For older scopes, first find the focal position for each eyepiece without the accessory and note whether there is sufficient remaining inward focusing range.

 

A second consideration is that very tall heavy eyepieces are not well suited for the HC focuser as the extra weight will require the friction adjustment screw to be tightened excessively, loosing some of the adjustment feel that is the whole point of the exercise.  Because my Lunar and planetary eyepieces are all quite compact, there are no issues for my application. Of course, one can also go back to relying on the original focuser as needed.

 

KineOptics charges a little over $100 for the HC-1A.  I don’t know the price for the custom “snout”, but it will certainly be quite affordable. 

 

JimC

 

 

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#2 BinoGuy

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Posted 20 November 2020 - 08:40 PM

Thanks, interesting idea.  I am confused about the installation.  In a straight through application would the spacers be needed? 

 

  http://www.kineoptic...C-1install.html

 

Thanks, BG. {°¿°}



#3 Mirzam

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Posted 20 November 2020 - 09:37 PM

The focuser is attached to the “snout” via 3 short bolts that pass through small tabs that protrude slightly from the snout inner wall.  The bolts screw into threaded holes on the red anodized ring.  I don’t think any spacers are involved.  When Joe made this unit for me he sent everything already assembled.

 

The air was a little turbulent this evening but the nice smooth focusing action helped to get the most out of the view.

 

JimC



#4 Jon Isaacs

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Posted 21 November 2020 - 05:42 AM

In a similar vein, there are non-rotating 1.25 inch helical focusers available that probably have finer control than the HC. 

 

https://www.cloudyni...-speed-focuser/

 

Jon




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