[Makers Mashup] shows in a video how to use an adjustable IR filter to cut out all the light bleed to get a sharp image to make focusing simpler. The filter he shows adjusts from 530nm to 750nm ...

(He notes that you might need to pull the IR filter from your camera to get a decent signal.) The pen is the usual IR LED with a power supply. To do the actual work, he wrote a custom application ...