Would collimated light help?

Well it might, but only if you know what it is, so go read “Measure Precisely with Machine Vision” by Ben Dawson of Dalsa and published on the Vision & Sensors web site (November 30th, 2009. Yes it’s an oldie, but it’s a goodie too.)

Don’t have the time or energy to click on the link I provided? OK, well let me summarize. You know how a telecentric lens improves the performance of a machine vision gauging system? (If not, search my blog for “telecentric.”) Well a collimated light complements the telecentric lens. Collimated means that all the light rays are travelling in the same direction, so you don’t get stray reflections off surfaces that are not facing the camera.

A good example would be when you want to backlight a shiny metal cylinder – when light rays are not aligned it makes the edge less sharp. Collimated light avoids this problem.

You can achieve nearly the same thing by placing the backlight at a distance from the object you’re gauging – the distance should be 2x or 3x more than the diagonal of the backlight so it becomes more of a point source – but it still won’t be quite as good. For ultimate precision you will need a collimated backlight.