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.