pic: Game hint

[Alan Anderson]

Originally Posted by Daniel_LaFleur

The problem with using a lens is that it has a focal length. The further away from that length you are (both closer or farther) the more defocused you get. Any single lens that gives you IR visability across the field will be out of focus up close (and may not be detectable). A zoom lens coupled with an PID circuit could allow you to focus at any length.

This isn't a camera. Being "in focus" is irrelevant. What an extra lens can provide here is a combination of directivity and light-collecting power. For this application, non-imaging optics are fine. It's the size of the lens that matters most, and the focal length is (to a point) unimportant.