DIY Laser levelling using webcam and laser level

[devmonkey]

John,

Great stuff. The latest version of the software allows you invert the intensity so it should work with a wire (as a shadow camera). You can also input a pixel to um scale (or inches or whatever) so it reads in your calibrated units rather than pixels. There is a preferences option in the menu. Note it leaves the webcam image unchanged performs the inversion on the intensity profile before fitting the gaussian.

FWIW the usb 1000x microscope I took apart to start this project at mid (say 100x) magnification is effectively 1:1 with the sensor area hence why it works so well without the lens. The magnification of these things seems to be defined as the multiplier of the subject size to screen size when displayed, i.e. it fully depends on the pixel pitch of your screen, thus should be largely ignored.

My screen is 1440 pixels tall and has a height of 330mm therefore a vertical pitch of 1440/330 = 4.36 pixels/mm. Given the 640 pixel height we are using this implies a screen height of 147mm, so without the lens a 2mm test subject that appears 147mm tall is equivalent to magnifying 73x using the above very ropey definition of magnification.

The depth of field of the usb microscope lens at the magnification you need is a few mm, should be sufficient. Non-linearity of your lens would have to be measured by focusing on a microscope scale, I have a couple of these that came with the cheepo usb microscopes.

To my mind much easier to think it terms of subject size to sensor pixel pitch, e.g. with no lens and 640 pixel rows over 2mm we get 3um.

Also something you must be aware of if trying to use a camera lens is that none of them are firmly fixed to the camera board meaning they will wobble and generate huge error as you move the camera around. The only solution I came up with for this was to find the focus/magnification you need then super glue the lens assembly in place. Also related is that the camera boards themselves are quite often not firmly fixed into the webcam cases causing the same problem. This is why I built a highly stable cube mount for the sensor (sensor is bolted hard to the delrin cube).


Cheers, Joe