DIY Laser levelling using webcam and laser level

[AndyUK]

The more I think about it, the harder it becomes! I'm not sure there is a good way to measure it without a precision straight edge as reference.

Essentially, I don't think it's worth worrying about - I say this because of how that lens is working - if the laser was a single point source then each bit along the horizontal line comes from a different part of the lens, and you'd be right to worry about lens defects causing wobble - but the laser isn't a point source, it has some width. This means that the contribution to any position along the horizontal is an average of a few positions on the lens, so any minor defects are smoothed out. Furthermore, the signal you detect is an average of the laser speckle, which is interference at the detector from a lot of different path lengths.

Not convinced? Okay, what happens if you move the laser slightly and repeat the measurement? If there isn't any systematic variation in the laser, you should get the same result. So my advice is average a few measurements with your system after moving the laser a few times; the standard deviation will be a combination of all your errors, including the wobble in the profile.

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