That sort of technique can be made to work but there are many traps for the unwary. Was involved on and off with pixel based position measurement systems for most of may working life as a scientist / R&D engineer for MoD. Usually as the guy doing the grunt lab work to prove why a bright idea didn't work as it should.

Bottom line is that it starts getting very tricky once you go below pixel size. Remembering that the nominal pixel size is the spacing not the actual image sensor. Also remembering that simple gaussian plots to determine the beam centre hide a lot of assumptions concerning pixel sensitivity variations, beam quality and even diffraction effects in the sensor structure. A colour sensor will completely crap things up.

Probably reliable to a thou or three with care and thought but below that you are in for serious work. I tend to agree with the rule that once you go below a thou things get serious. Fast. I've no doubt that it can be done if you throw the processing power of modern desktop / laptop or even smart phone computers at it. But its very easy to be blinded by the data deluge and loose sight of the fundamental physics. Back in the day we never had the luxury of so much computer power so had to think very carefully about the physics.

Correct approach is to micro-scan the beam image over the sensor so everything can be properly defined. Beam needs to be at least 10 pixels wide. Shed loads of data but at least you know what you are dealing with.

In general interferometer methods are much easier as fringes are robust over small errors and easily observed by cameras. Just needs a good way of converting displacement to tilt.

Back in the day when I had to align off axis paraboloids I would set up a small He-Ne gas laser on each axis and zero out the fringes produced by back reflection on the front mirrors on both lasers. Thats four sets of fringes bought coincident at both ends. But I really, really needed a foot diameter diffraction limited beam!

Clive

Edited By Clive Foster on 24/08/2019 12:06:20

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Very interesting project, John

You might see some useful improvement if you use a camera with an actual monochrome sensor.

MichaelG.

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Yes, Frances … that was my point

A monochrome sensor has one pixel per pixel [if you see what I mean]

A typical colour sensor [Bayer pattern] has four sub-pixels per pixel.

Gotta believe that the monochrome sensor will give crisper resolution.

MichaelG.

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For those unfamiliar with the Bayer pattern …

This is why (Red + Green + Blue) = 4

https://en.m.wikipedia.org/wiki/Bayer_filter

Edited By Michael Gilligan on 24/08/2019 16:59:19

Anyone who has seen my posts on autoguiding a telescope won't be surprised!

Neil

Thanks, John … Much appreciated

MichaelG.

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I have sent you a PM, John

MichaelG.

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That's great news, John … Keep up the good work

This looks like being a very effective spin-off from consumer technology !!

MichaelG.