The above is to illustrate the autofocus capability of a modded 20D in the Near IR. Canon 20D, clear glass with anti-reflection coatings over the sensor, plus a Wratten 89B gel used as a pop-in Front Filter. I.e. the camera sees only IR from about 720nm and longer. Since there's nothing visible in the viewfinder it's somewhat difficult to put the central focus spot where you want it, but with trial and error I managed to put it on one of the eyes. The plastic doggie's head is about 9cm in diameter and the camera was about 50cm away. Canon 100/2.8macro USM lens at f2.8. If you click on "original" below, you should be able to see the eye crop at 1:1. The thinnest lines are well under a mm wide. For other lenses see next slide.