Why not helical focusers?

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pakarinen United States of America
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Why not helical focusers?

#1

Post by pakarinen »


I'm curious why almost all scopes come with R&P or Crayford-style focusers as opposed to helical. Helical are much lighter, less complex and therefore more robust, and probably much cheaper to manufacture.

Just a random thought rolling around my brain like a pea in an empty coffee can...
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OzEclipse Australia
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Re: Why not helical focusers?

#2

Post by OzEclipse »


True helical only focusers have limited travel. The micro-focusers only have 10mm travel. If they did have long travel, they'd take forever to do a long travel unless combined with a draw tube slide.

My old telescope has a home made twist and slide friction focuser. Having used it for 44 years, I really like it and I am used to it.

Friends of mine using it for the first time have commented that once I explained how to use it, they really like it.

The brass tubes are a smooth twist friction slide. You twist as you pull or push, the resulting inward outward movement is very very smooth and fine, as precise as the Feather Touch on my 18" dob.
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Joe
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Amateur astronomer since 1978...................Web site : http://joe-cali.com/
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JayTee United States of America
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Re: Why not helical focusers?

#3

Post by JayTee »


The Telescopics focuser installed on my 8" Newt (circa 1972) is an R & P but the Rack portion is setup up to also function as a helical focuser for fine focus. Don't know why these aren't produced anymore, they work like a dream!
Newt Focuser.jpg
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
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∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°

Searching the skies since 1966. "I never met a scope I didn't want to keep."

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