Digital, Temperature Compensated Focusser.

Dave,

This sounds like a very impressive project. Just wondering (out loud) if the weight at the end of a refractor pointing at zenith, for example, would be stressing the system. My CCD camera very easily weighs a couple of kilograms and I do not know what kind of limits on weight, if any, there would be.

Hi Anthony,

The only additional weight at the end of a scope will be a single stepper motor. I bought a mini-hybrid motor which weighs a mere 140g.

ie.farnell.com/jsp/search/productdetail.jsp?SKU=8425868

A small aluminium bracket will also be required. I don't see the entire weight on the scope exceeding 200g. The electronics will be inside a small box/handcontroller which can be mounted elsewhere. So I don't see extra weight being a problem. Of course in a refractor the motor will attach to the main body and not the drawtube anyway.

Of course you may need to rebalance slightly.

Hi Dave,

I think I may have misled you! What I meant is how would the motorized focuser be able to handle a CCD camera weighing at least 2 kgs and with the telescope pointing overhead.

Thje other addition I thought of is a small microswitch so that the focusser can set a reference point. That way you could have the focusser return to presaved focus points very handy for visual users who could have presets for various eyepieces. Photographers could set average focus positions and allow software to tweak the focus to perfection.

Hi Dave,

I think I may have misled you! What I meant is how would the motorized focuser be able to handle a CCD camera weighing at least 2 kgs and with the telescope pointing overhead.

This was what I was getting at when I was asking if the motors are always energised or unpowered between focus moves. If the energised motors do NOT introduce any hum or vibration then you can effectively lock the focuser in place by keeping all the stators energised. That way you should be able to safely point the scope at the zenith with tens of pounds hanging off the focuser without having to worry about it slipping or drifting.

Phil.

Thats' a cool projects Dave, I look forward to seeing how it turns out.
I have a JMI-DX1 on my scope and would be interested to see if it could work with it.