Choosing lenses

There are two aspects to selecting a lens: figuring the focal length to suit both your camera’s sensor and the required field of view, and picking a good quality lens. The former can be done with the aid of a good machine vision lens calculator. (See “Updating the lens calculator link” or just use the search box to the left.) The latter requires an understanding of things like line pairs, MTF, and lens distortion.

I’ve already covered line pairs and MTF: “More on evaluating lenses” is a good start point. However I’ve never spent much time on lens distortion.

And I don’t need to, because over at Vision Systems Design magazine Andy Wilson has already done an excellent job.

“Understanding distortion in machine vision lenses” (also in the July/August 2013 edition of the magazine) explains terms likes “barrel distortion” and “spherical aberration.” It also has a handy set of links for “Further reading” on the subject of MTF.

Good though the article is, two things are left out. These are:

• How to pick a lens that performs well.
• What to do about distortion

If you’re looking for the answers to those, check back in a day or so.