jonnyastro
Carpal Tunnel
Reged: 02/14/06
Loc: Pittsburgh, PA
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Rack and Pinion focusers
#2151963 - 01/28/08 07:53 PM
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If the crayfords are so much better, why do you suppose high end companies like Tak and TeleVue are continuing to equip there scopes with rack and pinions? 
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1965healey
The Snarkster
Reged: 06/23/07
Loc: San Antonio, TX
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Re: Rack and Pinion focusers
[Re: jonnyastro]
#2152034 - 01/28/08 08:21 PM
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Cause they use REALLY good R&P's! 
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mikey cee
Postmaster
Reged: 01/18/07
Loc: bellevue ne.
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Re: Rack and Pinion focusers
[Re: 1965healey]
#2152108 - 01/28/08 08:43 PM
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  Mike
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jrcrilly
Refractor wienie no more
Reged: 04/30/03
Loc: NE Ohio
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Re: Rack and Pinion focusers
[Re: 1965healey]
#2152226 - 01/28/08 09:21 PM
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Cause they use REALLY good R&P's!
Yup. It's easier to build a good, inexpensive Crayford than a good, inexpensive rack & pinion - but ALL high-end focusers are rack and pinion, including the ones you list plus Astro-Physics and Feathertouch (only the light-duty, entry-level Feathertouch is a Crayford - their high-end models are rack and pinion).
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Rusty
Postmaster
Reged: 08/06/03
Loc: Brooker, FL
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Re: Rack and Pinion focusers
[Re: jrcrilly]
#2152333 - 01/28/08 10:07 PM
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The trick is that the high-end focusers use helical gears, not straight-cut spur gears as do the cheaper versions. Helical (spiral) cuts allow much more precision and little backlash.
Helical-cut gears require machining, whereas straight-cut gears can be made by die-cutting/stamping, much less precise.
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sparrow
Pooh-Bah
Reged: 02/10/06
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Re: Rack and Pinion focusers
[Re: Rusty]
#2152894 - 01/29/08 05:16 AM
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Just as a footnote:
I took a close look at the microscope my wife uses. It's a $12000 Zeiss (used) and everything on it is rack and pinion.
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jonnyastro
Carpal Tunnel
Reged: 02/14/06
Loc: Pittsburgh, PA
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Re: Rack and Pinion focusers
[Re: sparrow]
#2153432 - 01/29/08 12:56 PM
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Wow, i did not know that AP and feathertouch were rack and pinions.
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wprince
professor emeritus
Reged: 02/26/06
Loc: Atlanta, GA
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Re: Rack and Pinion focusers
[Re: jonnyastro]
#4551706 - 04/29/11 02:01 PM
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Old topic, but does anyone know of an manufacturer of higher end rack and pinion focusers for refractors. It seems as if everyone prefers Crayfords (and is only what seems to be readily available) and I'm not sure why...
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Trev
scholastic sledgehammer
Reged: 12/18/05
Loc: Fort McMurray, AB
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Re: Rack and Pinion focusers
[Re: wprince]
#4551762 - 04/29/11 02:23 PM
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Good crayfords are still cheaper to build than a high quality R&P, so for the average user upgrading to a crayford is a logical step.
A Feathtouch 2" R&P starts at $550 most people pay less than that for a very good crayford.
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Scott in NC
Mad Hatter
Reged: 03/05/05
Loc: NC
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Re: Rack and Pinion focusers
[Re: wprince]
#4551773 - 04/29/11 02:32 PM
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Old topic, but does anyone know of an manufacturer of higher end rack and pinion focusers for refractors.
Starlight Instruments, the company which produces the Feathertouch focuser.
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plyscope
Pooh-Bah
Reged: 11/23/06
Loc: Perth, West Australia
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Re: Rack and Pinion focusers
[Re: Scott in NC]
#4552116 - 04/29/11 05:41 PM
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Astro Physics sell their 2.7" rack and pinion focuser for $410. This is an excellent rack and pinion for refractors and is the same model used by D&G. There are many options available for it. Custom tube adaptors are available through Precise Parts.
Astro Physics web page
Andy
Edited by plyscope (04/29/11 05:51 PM)
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Eddgie
Postmaster
Reged: 02/01/06
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Re: Rack and Pinion focusers
[Re: wprince]
#4552156 - 04/29/11 06:05 PM
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I don't think EVERYONE prefers Crayfords.
It is just my opinion and my own experience, but the reason I think that some people prefer Rack and Pinion is because Crayfords don't seem to do as well when the load is very heavy.
When the load is very heavy, and especially if the weight is asymetric (31mm Nagler), I think Crayfords are more inclined to creep when aiming high overhead.
To counteract this, you tighetn the friction knob that holds the driving shaft on to the flat on the focuser tube.
When you do this though (my own experience anyway) the focuser knob can get a very rubbery feel to it.
And when you put a light weight eyepeice back in, the rubbery feeling doesn't go away, and of course the motion feels stiff.
High Quality R&P focusers seem to have a much wider range of holding power. For the heaviest eyepeices, or for camera gear, they hold much more positivly, and never get the rubbery feeling.
I have owned both Moonlight and Feathertouch. For someone using mostly lighter eyepieces and that doesn't hang a camera off the end, I think the Moonlight works fine.
For eyepeices like the 31mm Nagler though, the Rack and Pinion jsut seems to work much better.
No offense against Moonlight, but having owned both, I really do feel that the Starlight Instruments R&P are a more expensive but better option.
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jrbarnett
Eyepiece Hooligan
Reged: 02/28/06
Loc: Petaluma, CA
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Re: Rack and Pinion focusers
[Re: wprince]
#4552251 - 04/29/11 07:12 PM
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Feathertouch.
The best focusers from the best focuser producer are all R&P.
- Jim
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jrbarnett
Eyepiece Hooligan
Reged: 02/28/06
Loc: Petaluma, CA
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Re: Rack and Pinion focusers
[Re: Rusty]
#4552252 - 04/29/11 07:15 PM
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Even cheap, Chinese R&Ps like those sold by Antares, for example, feature helical cut gears. They work pretty well too.
Regards,
Jim
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Doug76
Long Achro Junkie
Reged: 12/05/07
Loc: Refractor Heaven
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Re: Rack and Pinion focusers
[Re: jonnyastro]
#4552463 - 04/29/11 09:37 PM
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Quote:
Quote:
If the crayfords are so much better, why do you suppose high end companies like Tak and TeleVue are continuing to equip there scopes with rack and pinions?
Cause they use REALLY good R&P's!
Indeed, as does Astro-Tech on the AT90EDT.
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Ed D
Carpal Tunnel
Reged: 04/30/10
Loc: Sunny South Florida
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Re: Rack and Pinion focusers
[Re: Doug76]
#4553370 - 04/30/11 11:58 AM
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Jim, sent you a PM about Antares focuser.
Ed D
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SkyscraperJim
scholastic sledgehammer
Reged: 07/29/07
Loc: Providence, RI
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Re: Rack and Pinion focusers
[Re: Ed D]
#4555354 - 05/01/11 03:28 PM
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Astro-Physics makes the best R&P focusers, Starlight is a close second.
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plyscope
Pooh-Bah
Reged: 11/23/06
Loc: Perth, West Australia
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Re: Rack and Pinion focusers
[Re: SkyscraperJim]
#4556117 - 05/01/11 10:39 PM
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For my 6" f15 I use a 2.7" A-P focuser. For my new 5" f15 project I will be using a Starlight FT 2535 because it is lighter than the A-P focuser and better balanced with the lighter lens. It's great to have the choice and Starlight certainly have plenty of choices available.
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: Rack and Pinion focusers
[Re: plyscope]
#4556143 - 05/01/11 10:57 PM
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A couple of random thoughts:
TeleVue also uses Rack and Pinion focusers. The NP-101 with the Feathertouch microfocuser is a very nice focuser and handles heavy eyepieces without sweat.
The Crayford design uses friction to more the drawtube. This makes it relatively easy to build a backlashless focuser but forever ties the load on the pinion to the load required to keep the focuser from slipping, heavy loads means the pinion bearings are heavily loaded which makes for a heavy action...
I wish someone would make a high quality, affordable ($200) rack and pinion with a 2 speed...
Jon
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Jon Isaacs
Postmaster
Reged: 06/16/04
Loc: San Diego and Boulevard, CA
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Re: Rack and Pinion focusers
[Re: plyscope]
#4556146 - 05/01/11 10:58 PM
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A couple of random thoughts:
TeleVue also uses Rack and Pinion focusers. The NP-101 with the Feathertouch microfocuser is a very nice focuser and handles heavy eyepieces without sweat.
The Crayford design uses friction to more the drawtube. This makes it relatively easy to build a backlashless focuser but forever ties the load on the pinion to the load required to keep the focuser from slipping, heavy loads means the pinion bearings are heavily loaded which makes for a heavy action... One of the issues with today's affordable Crayfords is that when preload is cranked up, the two speed microfocuser which are also friction drive tend to slip.
I wish someone would make a high quality, affordable ($200) rack and pinion with a 2 speed...
Jon
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