Infrared lens for thermal imaging rifle scope

Wavelength Infrared manufactured tens of thousands of infrared lens for Thermal Imaging Rifle Scopes every year, supplied to famous thermal scope brands worldwide.

Thermal scope can detect warm bodies from naturally cooler surroundings with their thermal contrast. Unlike traditional night vision scope, it does not need the support of background light to form a visual. Thermal scope can work day and night, cut through smoke, fog, dust and other environmental obstacles. Which make it special useful on hunting, search and rescue, or tactical operations.

Infrared lens is one of the core components on the thermal scope, integrated with a thermal sensor to convert the infrared image into electronic signals. Then the signals are converted to visible image to be displayed on OLED screen for human eyes. The clarity, distortion, brightness of the final image; the detection, recognition and identification range; the performance at different environment conditions, and even the reliability of the scope are directly affected by infrared lens. It is very important to choose a suitable infrared lens at the beginning of any thermal scope design.

While a suitable infrared lens is so important to a good thermal scope, there are also some core impacts to be focus on.

Focus Length (FL) and F#: The focus length of an infrared lens determines the DRI range of the thermal scope. In the other words, how FAR you can see. 25mm, 35mm, 50mm, 75mm are the most common focus length used on thermal scope. F# is the ratio of the system's focal length to the diameter of the entrance pupil, F# = FL/D. The smaller the F# of a lens is, the larger the entrance pupil is. More light would be collected by the lens while the cost goes up at the same time. Generally lens with F#1.0-1.3 are suitable for thermal scope application.

Sensor Type: Infrared sensor occupies a big share of the total cost of thermal scope. It determines how WIDE you can see with the thermal scope. Make sure the lens would match the resolution and pixel size of the sensor.

MTF and RI: MTF stands for Modulation Transfer Function, and RI stands for Relative Illumination. They are determined during design, which indicate the lens imaging quality. In the other words, how GOOD you can see. If not manufactured and assembled carefully, the real MTF and RI curve would be lower than which was designed. So make sure the MTF and RI of the infrared lens are tested before receiving it.

Coating: In general the outer piece of the lens is made of germanium, which is relatively soft and easy to be scratched. Standard AR (anti-reflection) coating won’t help on that, DLC (Diamond Like Carbon) or HD (High Durable) coating would be recommended to worked under harsh environment. But please notice that the total transmission of the infrared lens would be reduced at the same time. So you need to balance the two factors to achieve an acceptable performance.

Shock Resistance: Don’t like other thermal imaging applications, a thermal scope mounted on a rifle must be able to withstand the huge vibration caused by gun shooting. All the infrared lens for thermal scope we provide can meet >1200g shock resistant.