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
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.
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:
||Recommended Lens Diameter
||32 to 50 mm
||40 to 50 mm
|Heavy Machine gun
||40 to 50 mm
||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
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: