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C9.25 fine focus issues

Started by peterjtw, 05/31/2003 02:58AM
Posted 05/31/2003 02:58AM Opening Post
I love my C9.25, but the stock focus knob (the new black rubber type) binds on the sides of the hole in the focuser cover. Plus it just isn't precise enough for fine focusing at even moderate magnification. I don't want to add a whole new crayford style focuser. What I want is a new focus knob, possible a two stage design with gross/fine focus options. Anyone have any suggestions or experiences to relate? Thanks!
Posted 05/31/2003 04:00AM #1
You can replace the little nubbin' with a larger focus knob from focusknobs.com which will give you finer control for about $16. It is a direct friction fit over the stock knob and completely reversible. There is a photo of one on the scope over at the C9.25 Yahoo Group.
Posted 05/31/2003 05:45AM #2
I have seen people who have made dual speed focus knobs for their SCT's using commercially available vernier reduction drives and a little machining handiwork. Good luck finding the reduction drive, though! My guess is that if someone has made it for themselves, then it's commercially available. Unfortunately I have not seen any such product for sale.

I think the add on SCT focuser would be best though. Maybe try to find one used.
Posted 05/31/2003 12:42PM #3
I had a similar problem with my LX-90. I replaced the focus knob with a 2.5" diameter knob from EZ-Telescopes - which helped a lot with the fine focus. I tried the Meade electronic focuser - ditched it - tried the JMI NGF focuser - wouldn't clear the swing through at zenith - ditched it.

My problem after the bigger diameter focus knob was still very fine focusing and mirror shift - I found a helical focuser for about $100 solves the problem - and there's no clearance problem. Borg - and others have them.