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Double Helical Focusers

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4 replies to this topic

#1 jkevn

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Posted 23 January 2021 - 06:53 PM

Many helical focusers are referred to as "double". Does this mean an add-on to the existing focuser?



#2 SeattleScott

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Posted 23 January 2021 - 07:34 PM

Do you have an example? Not familiar with this.

Do you mean dual speed helical focuser? In which case the main focuser is rack and pinion, or possibly crayford. Then you use the helical focuser for fine focus.

Scott

#3 izar187

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Posted 23 January 2021 - 09:16 PM

If I'm remembering correctly, it is an outer barrel coarse threaded for faster movement of the ep, with an inner barrel that the ep goes in, which is finer threaded for fine tuning the focus. Outer barrel could also be helical crayford type with a fine thread insert.

I think. 


Edited by izar187, 23 January 2021 - 09:17 PM.


#4 Ulmer Spatz

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Posted 24 January 2021 - 09:05 AM

With focusing mechanisms for other optical instruments, there are "double helicoid" designs. This means that you can rotate the focusing ring with the glass remaining stationary in its own (second) ring. If "double" stands for "double helicoid," it could indicate a so-called non-rotating helical focuser. The eyepiece (or whatever else you stick into or attach to the focuser) does not rotate when you rotate the focusing ring.

 

But there is no standardization in astronomy gear terminology. And with unedited ad copy and machine translations nowadays, "double"  could mean all sorts of other things, like coarse / fine, rotating / push-pull, and who knows what else.


Edited by Ulmer Spatz, 24 January 2021 - 11:13 AM.

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#5 izar187

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Posted 24 January 2021 - 03:59 PM

Wow, sure does.

I was going from memory from when I was in the market for one.

Like this:

https://astromart.co...helical-focuser

 

 

But a search yields these:

https://www.google.c...iw=1309&bih=810




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