1. Lens

The lens is a plastic or glass focussing device, biconvex in shape. It is used to focus the infrared light from the infrared LED (12) into a tight beam to give long range. It is a very important component for achieving long range.

Generally the larger the lens the better the range, but it is also important that the lens is matched to the LED, so that it catches all or most of the Infrared light emitted. The matching is acheived by using a lens of the correct diameter and "focal length", the point at which the lens focuses at.

The focal length of a lens:


A typical lens assembly, taken from Dave Bodger's document here:


We recommend further reading of Dave Bodger's document here to learn about the lens calculations.


Lens Sizes

Different sized lenses can be used in a tag gun. As a general rule the larger the lens the longer the range, but the downside is that it then requires more accuracy to hit a target. Smaller lenses have shorter range and a greater spread allowing easier hitting of targets. This works fairly well in the laser tag context, in that guns like an SMG can have a smallish lens and be nicely suited to the usual tasks that a real SMG is used for, and a sniper rifle can have a larger lens that needs good marksmanship skills to land hits at long range.

Recommended lens sizes for different gun styles:

Gun Type Recommended Lens Diameter
Pistol 25 mm
Sub-machine gun 32 to 50 mm
Assault Rifle 40 to 50 mm
Heavy Machine gun 40 to 50 mm
Sniper Rifle 40 to 50mm


Focusing a Lens

The lens assembly must be focused correctly for best operation. The best range occurs when the led is sitting exactly at the lenses focal point. We suggest the following procedure to determine the best position for the LED:

  • Drive the led on continuously with low enough current not to damage it. This can be done by conecting the LED to a power supply or battery, along with a series resistor to limit the current. We suggest a 7.2 volt DC supply and a 100 ohm series resistor.
  • Setup a white peice of paper at a distance from the lens output, at least a few metres or more if possible
  • Setup an infrared-sensitive video camera (like a HandyCam with a "Nighshot" mode, or a security camera) to view the paper, and output the picture on a TV/monitor pointing back to the gun
  • Place the infrared LED near the lens, in a straight alignment with it, and adjust the LED closer or further from the lens until you get a bright clear focused image of the LED's own circular lens. Its possible also to focus on the LED's actual wafer, which results in a smaller, brighter but fuzzier spot however we've found greater range occurs when you focus the LED's lens itself. Look for a clear edged circle:


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