Every now and then new and old members ask about the Crayford Focusers that are on the GS scopes. I had read posts by other members saying they don't quite know the quality compared with other Crayford copies. I am very happy with mine but I am not in a position to compare with others as I have never used any other Crayford styles.
Here is a write up and photo I found which might answer a few questions for anyone contemplating buying the Crayford Focuser that the GS factory use on their scopes. It also explains what those 2 small recessed screws near the base are for and the correct use of the adjusting thumb-screws. I must admit that this write-up makes me feel even happier about my Crayford.
The TS Crayford focuser for Newtonian telescopes was designed to offer many improvements over other existing, similar looking focusers.
Advantages of the Crayford Design:
- ultra-smooth
- finely adjustable
- absolutely zero image shift
Improvements of TS Crayford focuser over similar focusers:
- more focus travel - 35mm instead of under 30mm. This alone solves many focus problems
- friction adjustment is achieved with a thumbscrew, not a slug screw that can only be operated with tools.
Specifications:
Weight: approx. 450 grams
Min. Height above tube: 73mm from base to top of 2" drawtube - extra height with 1.25" adaptor: 10mm
Focus Travel: 41mm - more than in other, similar looking Crayford focusers
Base Radius approx. 165mm. The focuser can of course also be attached to larger tubes, but there will be a small gap between the base radius and the tube.
The base is attached with four screws. Position of the four holes: 70mm x 72mm (parallel to tube axis x radial)
This focuser will directly fit onto your existing GSO, ICS-Galaxy, Hardin Optical Dobsonian as well as older Orion Skyquest Dobsonians.
You can turn the focuser to bring the two focusing knobs into a comfortable position easily - for instance 45 degrees in a Dobsonian telescope. Just loosen the two slug screws in the base, turn the focuser and tighten the slugs again.
Features 2" brass compression ring, adaptor from 2" to 1.25" with brass compression ring and 2" filter thread. The friction can be adjusted with a large thumbscrew. A second thumbscrew can lock the focuser tightly in position.
Locking Screw and Friction Adjustment:
When we compared our focuser with other, much more expensive focusers we were surprised by how smooth the focuser moves. Also, the friction adjustment turns out to be much easier since our focuser utilises a thumbscrew instead of a slug.
There are two large thumbscrews (see big image above). The upper thumbscrew locks the focuser - you can use very heavy accessories without fear of losing focus.
The lower thumbscrew regulates the tension of the focuser - at the easiest setting the focuser moves ultra-smooth like no other focuser we have seen so far. At tighter settings you can use heavy accessories without sacrificing much of the incredible smoothness of motion.
Customer Feedback
"I write regarding my recent purchase of a Crayford Focuser. It arrived very promptly and I am very impressed with its quality. I have not used it yet for astronomy (I am currently re-engineering a 10" Dobsonian into an equatorially mounted telescope for astrophotography), but I have no doubt that it will suit my requirements. I have two JMI Crayfords and have also used an Astrosystems Crayford recently. I believe yours is superior to all of these in build quality." - Paul
Hope that helps!!
