DIY Laser levelling using webcam and laser level

[Sasquatch]

My laser finally arrived, and...judge yourself.
camera fitted in precision vice riding on grade 00 18"x 24" granite.
Running across the beam i'm getting 0.04mm deviation from straight line on ~500mm distance
Running away from laser I'm getting 0.02mm deviation on ~500mm distance.
Beam is changing width and apparently this change is not symmetrical.
I was getting same results with pointer laser(runnig away from it), but assumed that irregular dot with surrounding artefacts was to blame.
It's still viable way of checking linearity, but as shadow camera and wire. Cheap(£25, glass lens, 80 MW) lasers are not precise enough. maybe £500 line laser could be used, but for such money there's plenty other options.

[devmonkey]

Do you have any pics of your laser and sensor? I think there is something strange going on with your setup if you see errors moving the sensor along the laser axis. Is the laser spreading? Have you removed all optics and filters from the sensor and bolted the pcb to something solid? We do know that the laser beam is not bending in the air so something else is wrong.