The mirror arm has to stop at exactly the same angle/place every time for this idea to work.  

I've tried to plan for this:

• The mirror arm and servo linkage are designed so the servo arm approaches the apex of it's travel when the mirrors are deployed.  This results in the mirror arm extending rapidly, but then slowing down just before seating on the hard stop.  It also gives me a huge range on the servo for fine tuning the pressure applied to the stop.
• I have the option of making the linkage spring loaded, or just using a digital servo as well.  I'm seeing how well the cheap servos work first.
• A large area, hard stop is included for the extended position.
• I used press fit real bearings with a little preload.
• Stainless pins anchor the arm, also press fit.
• The optics were aligned and then UV cure glued into place.

This seems to have worked.  For the video I was swinging the arm itself by hand from one side and driving the servo unpowered in the process to a random angle.  If you look carefully at the video, I was still looking right down the bore of my 2mmx50mm shaft straight enough nearly every time to see the circle of light from the other end.  

EDIT: I noticed the circle of light wasn't quite a circle.  Turns out I still had flashing from cutting the tubing on the end inside the brass bit.  Now.. it's a circle...  :)