Why you can’t get a sharp image

Most discussions of machine vision optics tend to focus (groan now please!) on lens focal length, working distance and depth of field. These are all important – critical even – in setting up a vision application, but often an engineer will zoom in on a region of the image and become instantly depressed. What looks sharp in the compressed monitor view often has a slightly fuzzy quality that no amount of focus ring adjustment can dial out.

The issue is diffraction. Ask an optics guru to explain and you’ll get a sermon on Modulation Transfer Function and a headache. So let me offer a different tack: grab a coffee and settle down with “Using Optics to Optimize Your Machine Vision Application,” (Vision & Sensors, December 2012.)

Frustratingly, Quality Magazine now expects you to register to read their articles, which I suspect is going to lose them some readers, but trust me, it’s worth it. Written by John Lewis of Cognex, this is an excellent article that will improve your understanding of how to get the sharpest possible image, and without all the equations Edmund Optics finds so necessary to explain depth-of-field, or DoF for short.

Now I’m going in the Edmund Optics site to get me one of those DoF targets. Or, now I’ve seen the price, I might just make one.