Hi all – I am after some advice for a focuser for a C8-SCT.
I am interested in both visual and astrophotography.
I like the look of the JMI focuser as they have a SCT threaded output adapter (so I can use my other SCT accessories) and they appear to have some good reviews on this and other astro sites.
I am not sure which model would be most suitable?
Should I go with a motorised version?
Are there other “better” focusers available?
Any comments and suggestions would be appreciated.
I have the motorised version Ian and I find its adjustment not really fine enough for imaging. It takes pretty big steps even when on it's slowest speed. I'm trying to work out a way to slow it down atm. Apart from that it is a fine focuser.
Mechanically, the JMI focusers are good value for money. As Paul indicates, out of the box the motorised version isn't designed for astrophotography. If you want something to get you started, buy a JMI focuser with no motor and adapt a Robofocus to it. This will provide very fine focuser movements (0.005" steps) so you'll easily reach the critical focus zone of the SCT. RoboFocus can be a pain to use for visual use as its typically slow, so you'll use your course focus knob more.
Slight catch though. If you calibrate the robofocus, you need to leave the course focus knob alone as any shifts using course focus with through out the RoboFocus calibration measurements if you are automating focusing. At this stage I don't think you need to worry about this.
Thank you Paul and Jase for your replies. Great information and gives me something to think about.
As another question - Can the JMI focusers be used manually for astrophotography? I was looking at the NGF-C or the EV-3c and these don't have a 10:1 fine focus. Is this needed? (I have seen that the GSO/Bintel and the WO focusers have this 10:1 fine focus.)
What would you suggest is better for astrophotography if you just went with a manual focus knob - do you need 10:1 fine focus?
Last edited by browndog; 27-08-2007 at 06:30 PM.
Reason: spelling errors....
The 10:1 is much preferred if going for a manual focuser (I refuse to say 10 times better ) as it makes focusing so much easier when you have to make VERY small adjustments, often fractions of a mm. Look around though as the are 10:1 focusers and then there are the other 10:1 focusers. ie they don't all come out of the same mould
![[1ponders]'s Avatar](../vbiis/customavatars/avatar45_9.gif){kind=avatar}
) as it makes focusing so much easier when you have to make VERY small adjustments, often fractions of a mm. Look around though as the are 10:1 focusers and then there are the other 10:1 focusers. ie they don't all come out of the same mould 
