DIY Laser levelling using webcam and laser level

[AndyUK]

Ah, so you're worried about the wobble in the horizontal projection. The thing is, because of the way the laser leaves the slit, it's going to be quite smoothed out.

If you just swoop left to right with the pipe and it stays within the meniscus, you're laughing. A 4m projection distance and a 2mm meniscus means that you'd be within 0.05mm (back of the envelope..), which is on par with a ~£100 precision straight edge. To know if it's better than that, just increase the distance further and further - if you can extend it to 10m you're down to <0.03mm for example.

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[devmonkey]

Ah, so you're worried about the wobble in the horizontal projection. The thing is, because of the way the laser leaves the slit, it's going to be quite smoothed out.

If you just swoop left to right with the pipe and it stays within the meniscus, you're laughing. A 4m projection distance and a 2mm meniscus means that you'd be within 0.05mm (back of the envelope..), which is on par with a ~£100 precision straight edge. To know if it's better than that, just increase the distance further and further - if you can extend it to 10m you're down to <0.03mm for example.

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Thanks for persevering with me Andy. This is what I mean imagine the laser line generator is aimed at a wall and we are looking at that wall:

So given we know that the 'self levelling' laser is going not going to be perfectly level to earth, we want to check the error between the generated line (red) and a true straight line (blue) to determine how straight our generated line is.

These lasers generate lines by firing through a cylinder of glass mounted vertically in front of it, when the light leaves the curved surface it refracts in one dimension causing it to fan out, therefore projecting a horizontal line. The glass cylinder cannot be perfect so there must be some imperfection in this projection. Any idea how much before I bother trying to measure it?

Or am I missing some fundamental understanding and that the physics implies the line generated will always be perfectly straight?