"Robert Rolf" wrote
> DC controlled camera lenses are basically milliampmeters.
>
> A mechanism similar to a meter movement opens the iris against
> a closing spring force. The 'drive' is a variable CURRENT to
> make the circuitry simple and not dependent on absolute coil resistance.
> And the magnetic force is a function of CURRENT since the coil is
> quite inductive.
> The 'control' winding is used as velocity feedback to damp the
> coil motion, by reducing the drive current as the iris moves, to
> prevent overshoot.
>
> You can dive the lens using a variable voltage source with a current 
> limiting
> resistor into the 'drive' terminals.
> Hang a scope on the 'control' leads to see the back EMF the moving coil
> generates. If you short out the control winding you get maximum damping,
> which is probably what you want for your basic voltage control.
>
> Robert


That makes sense. I'll do a couple more tests tonight.

So, if I want to make a control circuit that simulates a manual iris and its 
f-stops (supposing that I have a way to calibrate an actual iris aperture to 
an f-stop), I'd have to use the control as feedback right? As you can tell 
I'm a newbie with electronics, so what should I use for that, an opamp?

Thanks a lot!

Padu 

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