mahmood Elnasser wrote:
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Steve:
controlling the mirror is a very good idea and is worth me looking into it.
Thanks. It will depend on the lens of the cmaera to some extent too.

What you are doing is effectively an Adaptive optics problem and you are correcting for the 0th and 1st order abberations of the Zernike polynomial. I can't remember the exact URl, but look around opt.phys.ic.ac.uk for some good stuff.
A Zernike polynomial is a mathmatical method of describing the shape of an optical wavefront.
The 0th and 1st terms of the Zernike polynomial are simply tilt in the X and Y planes, Tip and Tilt exactly those you would want to correct for objects >>>2 x focal length of the lens. They can't handle translation of the image, just rotation.

Correcting 0 and 1 only require a "copy" of the image on a sensor. A half-silvered mirror is placed between the tip/tilt actuator and the camera. The sensor servos the centroid of the image onto itself.For sensor think webcam perhaps ? FPGA to pull the data out of the sensor CCD ?

Where can I get a voice coil from to start experimenting?
A reasonably big woofer ? The power rating of the woofer is the power handling of the coil.

would a standard hi-fi speaker do the trick?

For a hacky little try out, easily. You might, if you can scale it all use voice coil motors from hard disk drives.

Would the dc voltage damage the voice coil or not?
No, Bear in mind that Current controls the displacement of the coil, not voltage. We usually drive with constant voltage because there is then a "damping term" which stops the coil oscillating when it is excited, which without feedback for a hi-fi is what we want. To speed things up, you use voltage controller current sources. But your feedback needs to be REAL good !!


kunal:
What i will be doing here is having a closed loop control system, that means i will be having feedback and all the inertias of the components taken care of.

Subject to the power needed to wank the mirror about......


Mahmood, when you get it working, can I have a small one for my telescopes !


Steve