What is a "Crayford" focuser?

[yagon]

Can someone please explain what a "Crayford" focuser is, and how it is different from a "Rack and Pinion" focuser?

[Dennis]

Have a look here for Crayford.
http://www.astronomics.com/main/category.asp/catalog_name/Astronomics/category_name/GPPM30TX16PT8MEGHTP24W1JD4/Page/1

Here is another nice Crayford site too:
http://www.aqua.co.za/assa_jhb/new/Crayford.htm

Nice animation of a R&P here:
http://en.wikipedia.org/wiki/Rack_and_pinion

Cheers

Dennis

[yagon]

Thanks for the links: I understand now.

[Dennis]

No worries. In terms of user tests, I have a R&P focuser on my Vixen 4 inch refractor which is well made and doesn’t suffer from any noticeable looseness or play. However, sometimes it can be a little difficult making a tiny tweak to the focuser position as the resolution between the turns is too coarse.

A Crayford has a continuous, smooth movement and I have a JMI NGF Crayford focuser which I find is much easier to make tiny movements.

Some newer models, such as the WO dual focus Crayford models, have a coarse focus and a 10:1 fine focus, although I have never used one of these.

Cheers

Dennis

[ving]

while sorta on topic...

anyone know the weight diff between the gso cray and r n' p?