I make a lens assembly that can offer a range of about 800+ ft. and here is how I do it.

First of all, the lens: I use a two inch dia. lens that I buy from All Electronics. The part number for this lens is MGN-1. It looks like a little magnifying glass with a black handle, but the handle can be removed. You can order these lenses from All Electronics by calling 1-800-826-5432.

They cost $1 each.

Okay, the infrared focal length for these lenses is exactly 4.5 inches, in other words, the tip of the LED should be exactly 4.5 inches from the back of the lens. I suggest using a Siemens sfh484-2 infrared LED since it has a 10 degree spread and works perfectly with the focal length and diameter of the lens.

Now, the tube: I generally make mine out of central vacuum tubing. It comes in 10 ft lengths at Eagle Hardware. I cut these to exactly 4.5 inches long and that works well. This type of tubing is a good choice because it is the right diameter, very thin walled and therefore lightweight. There are also fittings (used to connect long sections of 10 ft tubes) for the ends of the tube that can be used to hold in the lens and to hold a plate in the back where the LED goes.

I generally cut a 2" dia disc out of plastic for mounting the LED holder into for the back of the tube. Drill a hole in the center of the plastic and mount an LED holder to hold the LED. You can get these LED Holder bezels from Radio Shack.

I just put the lens at the front of the 4.5 tube and the plastic disk in the back and add the fitting to hold everything together. I have pictures of the lens assemblies that I sell on my web page and you can take a look at them for a better idea of what they look like.