Re: ATM Must...avoid...helical...focuser..must...make...crayford

[andydtg@phoenix.net]

Tom Stock wrote:

>     I recieved my helical focuser finally...after using it for about 30 
>     seconds I realized I should have made a crayford type out of wood and 
>     PVC (or aluminum).  Even on a 6" F4 it took too long to get an 
>     eyepiece in focus.  Adding a barlow was nothing less than frustrating.
>     

I built a '2-speed' helical focuser once for an RFT, it had shallow
grooves with a circular profile on the eyepiece holder tube rather
than the usual v threads. The threads were about 4 or 5 per inch,
about 1/16" deep.

The ID of the focuser body was not threaded, there was a spring loaded
ball bearing the same dia as the thread profile (1/4"). Coarse
focusing was done by sliding the barrel in or out, the ball would
allow it to skip over the threads. Rotating the barrel caused it to
work like a regular helical.

(apologies to Tom, intended to send this to the list..)



Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net