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!!
Last edited by ballaratdragons; 26-09-2005 at 09:18 PM.
l would think any crayford style focuser will be an improvement over rack and pinion, every one l have had has always worked well, in the recent past l've had the Orion ED80, the W.O Zenithstar and the W.O 2" for my Meade and they are all very very smooth.
While we are discussing Crayford Focusers, I found a site that gives step by step instruction on modifying the focuser used on the Orion 80/100ED scopes. The basic mod is to improve the finish of the flat on the Orion ED Crayford on the 80/100ED. This mod will allow the focuser to hold a real load of at least 5lbs. If you are interested just follow the link; http://finefocuser.com/orionedcrayfordm.html
The only thing going against Crayfords vs good R&Ps is that they are so smooth they need a lot of tension to hold focus in a refractor with a 2" diagonal + eyepiece when pointing about 45 degrees above the horizon. (It just slides all the way out.) Under so much tension it requires quite a lot of torque to move the focuser in (lift focuser + diag + EP), no more feather touch. Worst at zenith of course.
I'd hate to think what of heavy prism diag + 31mm Nagler hanging off it at zenith would handle like.
I'd still prefer Crayford any day though. And for the Dob it would be perfect.
The only thing going against Crayfords vs good R&Ps is that they are so smooth they need a lot of tension to hold focus in a refractor with a 2" diagonal + eyepiece when pointing about 45 degrees above the horizon.
Thats probably why the seconds screw is for locking the focuser once you get it nailed.
I have a R&P on my smaller dob and a crayford on my bigger - no comparison, the crayford kicks the snot out of the R&P in every way!!!
I've also used friend's dobs with upgraded R&P's with all sorts of doodads added to them to help with fine focusing and such. The inexpensive (not cheap) GSO crayford kicks the snot out of them too
I'm too scared to do the mod... Plus it works anyway. It just works a lot better when level, with a beautiful feather touch & no tension is required (the weight of the focuser resting on the roller is enough then).
Where can one buy a GSO Crayford Focuser and how much are they?
I have the R&P on my GS0 10" and am wondering if this is a simple switch or needs some drilling hacking etc.
Where can one buy a GSO Crayford Focuser and how much are they?
I have the R&P on my GS0 10" and am wondering if this is a simple switch or needs some drilling hacking etc.
Crayford Focuser - the facts
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Enough said.
