I experimented with IR focus and the results were interesting. The circuit published in my previous post could detect IR from the gun at about 50m without a lens to focus it. My plan was to get as far away from the test circuit as I could until it failed to detect a transmission, then adjust the focus until the sensor saw the IR pulse again, then move further away.
Unfortunately, I was unable to get far enough away from the sensor in my test environment! I resorted to the IR camera and got a satisfactory beam focus by visually examining the size of the beam on my monitor.
I haven't built the IR sensors yet, but I decided to build the milestag gun up fully. It went together well. I also fitted a picatinny rail to the top of the gun and fitted a cheap red dot sight I got from ebay.
It looks pretty good. Trouble is, I now need to paint 60% of it bright orange to conform with UK imitation gun laws. Ah well.....