OK, I'm going to expose my ignorance here. I know that crayfords are good, but what exactly are they? What makes them so good?

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

They use friction alone, rather than a rack and pinon like most other focusers.

So the good ones move smoothly, with no slop or jerkiness. Good ones also have multiple speeds, with a fast and a slow control.

I absolutely love the one I put on my home built Dob.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

The Starlight Instruments dual speed Feather Touch is one of the best focusers available.

http://www.starlightinstruments.com/

MoonLite makes some very fine Crayford focusers that aren't quite as expensive.

http://www.focuser.com/storefront.php

Dave Mitsky

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Very nice Dave...but I'm not looking to buy one right now. I was just curious as to how they work!

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

See this link for the design info.
http://www.astronomics.com/main/cate...24W1JD4/Page/1

Rick

try this if you need more detail and are thinking diy.....
http://www.atmsite.org/contrib/Sapp/.../CrayFocus.htm

Highly recommended I have one on my WO scope with a 10:1 ratio on the fine focus.

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But you're sure the astronauts are lying; you just don't seem to know what they're lying about. jayutah