A little bit more experimentation, some good news and some irritation. Firstly I stripped the sensor out of the microscope and used it without a lens, to my surprise this works very well. Effectively we are using the cmos sensor as a very high density light detector, it seem undamaged with direct exposure to the laser beam. This also means I can repackage it in a nice compact unit.

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The new issue that has appeared having removed the optics entirely is that this Dewalt laser level is crudely modulating its beam. I presume this is some sort of vendor lock in mechanism so that if you buy a Dewalt detector it will only work with Dewalt laser, or maybe i'm being unfair and it is to discriminate the laser source from other light ;-) Anyway this screws up the rolling shutter on the cmos image sensor, you can see the banding in the left hand frame grab below, not present in the next frame.

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So either I need to detect and discard frames that contain this banding, open the laser level and disable the modulation or buy a laser line generator from amazon for a couple of quid, although this wouldn't be a self levelling pendulum, which will make setting it up more of a hassle. On the last point although the dewalt unit is self levelling this isn't useful as a repeatable (between measuring sessions) reference plane, it just means the reference plane generated between switching the laser on and off after the session is roughly (~0.3mm per meter) level with earth.