The meaning of Spot Size of the IIT and the consequences for pricing.

Harder HD-2102A

The Harder HD-2102A intensifier tube is a “GEN-2 Premium” device. GEN-2 night vision typically uses an S-25 (extended red) photocathode and a micro channel plate (MCP) to achieve gain and either electrostatic or fibre-optic inversion. These tubes provide satisfactory performance at low light levels and exhibit low distortion.


Photocathode. The input surface of an image intensifier that absorbs light energy, which in turn, releases electrical energy in the form of an electron image. The type of material used is a distinguishing characteristic of the different generations of image intensifiers.

Micro Channel Plate (MCP) current amplifier. A metal-coated glass disk that multiplies the electrons produced by the photocathode. An MCP is found only in Gen II and Gen III systems. These devices normally have anywhere from 2 to 6 million holes (or channels) in them. Electrons, entering a channel, strike the wall and knock off additional electrons which in turn knock off more electrons producing a cascading effect. MCPs eliminate the distortion characteristic of Gen 0 and Gen I systems.

Automatic Brightness Control (ABC). An electronic feature that automatically reduces voltages to the micro-channel plate (MCP) to keep the image intensifier’s brightness within optimal limits and protect the tube. The effect of this can be seen when rapidly changing from low-light to high-light conditions; the image gets brighter and then, after a momentary delay, suddenly dims to a constant level.

Bright Source Protection (BSP). An electronic function that reduces the voltage to the photocathode when the night vision device is exposed to bright light sources such as room lights or car lights. BSP protects the image tube from damage and enhances its life. However, it also has the effect of lowering the resolution when operational.

Spot Size

In fact, the difference can be found in the amount of so called “black spots”. These are cosmetic blemishes in the image intensifier or can be dirt or debris between the lenses. Black spots that are in the image intensifier do not affect the performance or reliability of a night vision device and some number of varying size are inherent in the manufacturing processes. Spots due to dirt or debris between the lenses should be removed by careful cleaning (if the system is designed for interchanging optics).

Simply put; the Harder “More Expensive” type can be compared with the most expensive GEN-3 tubes. The “Less Expensive” type can be compared with lower-end military grade GEN-3 tubes.

Our Night Vision Product Range

You can find examples of our current product range together with more information on night vision. For a more comprehensive overview of our night vision products visit our catalogue

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