Mounting a Lens

The choice of a lens depends on the mounting method, and the mounting method depends on the lens chosen.

Requirements

A lens mount must do several things:

Pipe Mounts

Many casings use a length of aluminum or plastic pipe as the foundation of the lens mount. The pipe is chosen to be sturdy enough to hold the lens and IR LED securely, and to protect them from damage. The pipe is mounted to the casing so as to look like a part of the weapon, either as a silencer, an underslung grenade launcher, a part of the grip or barrel, or some other tubular part of the weapon. The sights, either "iron" sights or a scope, are usually attached to the casing separately, but are kept in fixed alignment with the lens mount by rigid casing elements.

A lens can be mounted to a pipe by trapping the lens between two supports inside the pipe, or it can be trapped on the face of the pipe with a fitting.

Inside

Inside lens mount, bracket LED mount

The inside pipe mount places the lens inside a length of pipe. The lens is supported against lateral motion by the walls of the pipe. The lens is prevented from moving longitudinally by putting a cylindrical support on either side. The cylindrical support can often be made by cutting a short length of plastic pipe of the same diameter, removing a small section of it to form a "C" shaped piece, and then sliding the C-shaped piece inside the pipe. Care should be taken to make sure that the face of the C that touches the lens is perpendicular to the axis of the pipe. That way, the lens fits squarely in the pipe rather than at an angle.

Face

Face lens mount, disk LED mount

The face pipe mount places the lens against one end of a length of pipe. The lens is supported on one side by the front of the pipe. A fitting with an interior flange is placed over the end of the pipe, trapping the lens against the interior flange. Care should be taken to ensure that the front face of the pipe is perpendicular to the axis of the pipe. That way, the lens will not be held at an angle.

LED Mount

There are at least two popular methods of holding the IR LED centered in a pipe. The first places the LED inside a bezel, and mounts the bezel to an L-shaped piece of metal, wood, or plastic. The L is then attached to one wall of the pipe, and often made so that it can be moved along the pipe to allow focussing. The second method places the LED inside a bezel, and mounts the bezel to a disk of metal, plastic, or wood. The disk is sized so that it fits snugly inside the pipe, and secured with a screw or pin. Sometimes the disk is attached through a slot, so that the disk can be moved along the pipe to allow focussing. In either case, care should be taken that the IR LED is centered in the pipe, and is facing along the axis of the pipe.

U.S. Pipe Diameters

If the lens is to be mounted inside or in front of a pipe, it's important to match the diameter of the lens to the diameter of the pipe. For an "inside" mount, the lens diameter must be very close to, but not larger than, the pipe inner diameter. For an "in front" mount, the lens diameter must be very close to, but not larger than, the pipe outer diameter.

This table gives the sizes of various standard pipes in the U.S. The official "pipe size" is given in inches, but typically does not match the actual size of the pipe. For a given pipe size, the outer diameter (OD) is constant, and the inner diameter (ID) varies with the wall thickness. The "schedule" gives the wall thickness and inner diameter for a given pipe size; these also vary by pipe size for a given schedule.

Pipe Size Pipe OD Schedule 10 Schedule 40 Schedule 80 Schedule 160
Pipe ID Wall Pipe ID Wall Pipe ID Wall Pipe ID Wall
1/8″ 0.405″
10.29mm
0.307″
7.80mm
0.049″
1.25mm
0.269″
6.83mm
0.068″
1.73mm
0.215″
5.46mm
0.095″
2.41mm
1/4″ 0.540″
13.72mm
0.410″
10.41mm
0.065″
1.65mm
0.364″
9.25mm
0.088″
2.24mm
0.302″
7.67mm
0.119″
3.02mm
3/8″ 0.675″
17.14mm
0.545″
13.84mm
0.083″
2.11mm
0.493″
12.52mm
0.091″
2.31mm
0.423″
10.74mm
0.126″
3.20mm
1/2″ 0.840″
21.34mm
0.674″
17.12mm
0.083″
2.11mm
0.622″
15.80mm
0.109″
2.77mm
0.546″
13.87mm
0.147″
3.73mm
0.466″
11.84mm
0.187″
4.75mm
3/4″ 1.050″
26.67mm
0.884″
22.45mm
0.109″
2.77mm
0.824″
20.93mm
0.113″
2.87mm
0.742″
18.85mm
0.154″
3.91mm
0.614″
15.60mm
0.218″
5.54mm
1″ 1.315″
33.40mm
1.097″
27.86mm
0.109″
2.77mm
1.049″
26.64mm
0.133″
3.38mm
0.957″
24.31mm
0.179″
4.55mm
0.815″
20.70mm
0.250″
6.35mm
1–1/4″ 1.660″
42.16mm
1.442″
36.63mm
0.109″
2.77mm
1.380″
35.05mm
0.140″
3.56mm
1.278″
32.46mm
0.191″
4.85mm
1.160″
29.46mm
0.250″
6.35mm
1–1/2″ 1.900″
48.26mm
1.682″
42.72mm
0.109″
2.77mm
1.610″
40.89mm
0.145″
3.68mm
1.500″
38.10mm
0.200″
5.08mm
1.338″
33.99mm
0.281″
7.14mm
2″ 2.375″
60.32mm
2.157″
54.79mm
0.109″
2.77mm
2.067″
52.50mm
0.154″
3.91mm
1.939″
49.25mm
0.218″
5.54mm
1.689″
42.90mm
0.343″
8.71mm
2–1/2″ 2.875″
73.02mm
2.635″
66.93mm
0.120″
3.05mm
2.469″
62.71mm
0.203″
5.16mm
2.323″
59.00mm
0.276″
7.01mm
2.125″
53.98mm
0.375″
9.52mm
3″ 3.500″
88.90mm
3.260″
82.80mm
0.120″
3.05mm
3.068″
77.93mm
0.216″
5.49mm
2.900″
73.66mm
0.300″
7.62mm
2.626″
66.70mm
0.437″
11.10mm
4″ 4.500″
114.30mm
4.260″
108.20mm
0.120″
3.05mm
4.026″
102.26mm
0.237″
6.02mm
3.826″
97.18mm
0.337″
8.56mm
3.438″
87.33mm
0.531″
13.49mm
5″ 5.563″
141.30mm
5.295″
134.49mm
0.134″
3.40mm
5.047″
128.19mm
0.258″
6.55mm
4.813″
122.25mm
0.375″
9.52mm
4.313″
109.55mm
0.625″
15.88mm
6″ 6.625″
168.28mm
6.357″
161.47mm
0.134″
3.40mm
6.065″
154.05mm
0.280″
7.11mm
5.761″
146.33mm
0.432″
10.97mm
5.189″
131.80mm
0.718″
18.24mm
8″ 8.625″
219.08mm
8.329″
211.56mm
0.148″
3.76mm
7.981″
202.72mm
0.322″
8.18mm
7.625″
193.68mm
0.500″
12.70mm
6.813″
173.05mm
0.906″
23.01mm