Quote Originally Posted by devmonkey View Post
Hi John,

Do you have a picture of the 'polygon' prism from the laser printer? Is it a penta-prism? If so then this would be suitable, if it is just a 90 degree mirror then we wouldn't be able to align it accurately enough. I have been looking for a penta prism, we would need an accurate one, most are specified in arcminute accuracy but the super precision ones are around a few arcseconds. I'm guessing this means is that over 1 meter the error in height measurement due to the prism would be:

1 arcminute: 290um (a massive 0.29mm)
1 arcsecond: 5um

So this begs the question, how accurate are these super expensive industrial machine levelling metrology systems that use lasers? What I have now with the cheap laser and camera sensor is within say 50um per meter, given there is a limit on the precision of the prism are the industrial products really much better than this?

Cheers, Joe
To answer my own question, this system:
https://www.hamarlaser.com/systems/l...th-plumb-beam/

Has a stated accuracy of 0.5 arc seconds (2.5um per meter):
Laser plane flat to 0.5 arc second (.00003 in/ft or 0.0025 mm/m).

No idea about price but can't imagine it is cheap!