>
>
> Seriously, anyone doing this kind of contactless distance  
> measurement is
> using optical interferometry. A laser diode, a beam splitter, a corner
> reflector and a pair of phototransistors with a quadrature decoder  
> to count
> fringes.
>
> Now, the OP did say "resolution" and not "accuracy", so maybe there  
> isn't
> a requirement for measuring the total span accurately, just changes in
> distance.
>
> -- Dave Tweed

Dave
Could you tell me more about practical optical interferometry ?  Have  
you built such a device ?  Are there parts or kits to do this that  
cost less than $100 / $200 / $500 / ??? to do this ?  Are there any  
diagrams showing this setup ?
Best
Gus
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