S.A.- I narrowed it by an inch on each side.It seemed to do the trick in testing, but all I have gotten is false triggers in the field(109 degree heat) I put a thermostat on my cam and put it back out this morning, so we'll see how it works now. Scott
Simple - I use a piece of black tape (about 3/4") on each side of the pir on my cams with the entire pir lense exposed. Lately I've been using a 1" hole with the PIR lense mounted flat to the inside of the cover. This has worked well for me here in PA - but it's only around 80 degrees or so.
I had cut out some pices of plastic and used electrical tape to hold them in place. Today I was testing my camera. I was about 20 ft. away. I checked my field of detection using the LED. It was a narrow range considering that there is a delay in the canon owl pf date when you don't refresh it. So I took my shilelds on each side of the ms20 fresnel lens,off. I did not notice much improvement. It might be different closer in or maybe it is the temperature.
S.A. - If you want to shorten the range a little to get it more in tune with the flash, D.V. Shooting posted a picture of his 3rd Edition Trail Cam. That guy sure took some good pictures with it. I tried the same configuration with the bottom roll of the fresnal lens taped off, and it seemed to have less false triggers.