9.25 SCT focuser issues

My 9.25 SCT came new with a slight defect in the focuser shaft. It rubs while turning and always in the same spot. Not a big deal but it does make fine focus a problem.

So instead of fixing it, I figured maybe I'd get the feathertouch micro focuser. Then I found the JMI motor focuser for a little less money. I thought maybe the motor focus would be nice for hands off and maybe if I do astrophotography I'd be a step ahead.

So I'm leaning toward the motor focus. Thing is, I don't know if I'd like it. Always having to use the controller and no ability to move the focus by hand, I think, may not be something I'd care for.

Also, I don't know if the motor focus can be adapted to a computer for control.

Any comments would be appreciated. Any other options would be great as well. I've enclosed a picture of the JMI unit I'm looking at. Joe Conway

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Lots of things to say, here, Joe.

The motofocus is a step forward, but will not get you all the way you want to go. The Motofocus attaches to your regular focuser knob, and just replaces your hand. This is great because you no longer have to get up and touch your scope when focusing (and thus shake it). But it is a DC motor and controller. It is hard to get an exact focuser position by the very nature of dc electronics. Also, you stil get mirror shift, and backlash problems. On the other hand, it is easy to use, and you will find you do not really need to remove it (in short they work well enough that you do not need "manual" focusing). But if you choose to remove it, it is fairly simple. It can be controlled from a computer, and interfaces with various automated focusing programs.

An additional focuser on the back of your SCT would help with fine focusing and astrophotography. You would do a rough focus with the C9.25 existing focuser, then refine it with the fine focuser. Therefore, you would not have to worry about the flat spot in the current focuser. This arrangement also overcomes much of the mirror shift and much of the backlash issues one gets when using a standard SCT focuser. (Not all of them!)

And of course, you could put a motor on your auxiliary focuser. Therefore you could use your main SCT focuser to do a rough focus, and your auxiliary focuser with the motor do do the fine, hands-free focusing (again, interfacing to computer automation).

One other thing to think about. There are two general types of motors running focusers. One is dc, the other stepper. Both are very good, but the stepper generally moves in very specific amounts with each pulse. Therefore, your focus position is more precise.

Hope this helps.

Alex

Joe,

Sometimes the problem you describe can be fixed by simply loosening all three screws on the focuser shaft and retightening by torgueing each screw evenly. If the shaft is bent, this won't work, but it may be that the screws were tightened one at a time at the factory causing this problem. I have seen it several times before.