Crafords and 2 inchers

Chaps,

Seeking to change the foccuser on my 250 newt and would like to know the
differences/opinions on the Craford style and standard rack and pinion
style! From what i can see the Crayford is still a rack and pinion isnt it?

Also when it comes to 2" ep's i seem to only be able to find own to 20mm
before they become divorcingly expensive, are there cheaper smaller ones
availible?

Thanks

Rob

Rob

You may need to scroll down! ;-)

A Crayford focusser relies on a friction drive where a rod is rotated
while pressed hard against the draw tube to produce slow, stepless
linear motion. Normally the draw tube is made of stainless steel to
ensure that friction is high enough to accept the drive from the rod
(or axle) which connects the focussing knobs. The pressure from the rod
is resisted by four rollers or ball bearing races placed on the other
side of the draw tube from the drive rod.

I made a 2" Crayford with a polished brass focussing tube and found the
friction was not high enough unless the rod was covered in soft plastic
tube. But then the plastic tube flattened under the pressure when
static producing a bumpy action. Replacing the brass with stainless
tube solved the problem. Though I still prefer brass for aesthetical
reasons.

Ensure your choice has sufficient travel to focus a variety of
eyepieces including the use of a Barlow lens or camera body.

Regards
Chris.B

"Robert Geake" wrote in message
...
Chaps,

Seeking to change the foccuser on my 250 newt and would like to know the
differences/opinions on the Craford style and standard rack and pinion
style! From what i can see the Crayford is still a rack and pinion isnt
it?

Also when it comes to 2" ep's i seem to only be able to find own to 20mm
before they become divorcingly expensive, are there cheaper smaller ones
availible?

Thanks

Rob

If you are willing to go used you might find a better price. Also, I
have seen some 1.25 " eyepeices advertised that are designed with much
larger than usual
viewing aperture, even for the higher powers, at relatively inexpensive
prices. You may have to do some serious research on the web to find exactly
what you want, though.

Bill.