With our first post we will start with some basic terminology used by Night Vision NZ. We will provide more in depth information on some of these terms in future posts. We have broken Night Vision down into the two main types available in New Zealand, Digital and Thermal.
TERMS RELEVANT TO DIGITAL:
Digital night vision devices rely on reflected light invisble or near inisible light from a built in or external light source that is then captured by the CMOS sensor and displayed on the OLED or LCOS screen. These devices tend to be more affordable than thermal and generally have a much better image resolution but with the trade off of beiung shorter range.
A Complementary Metal-Oxide Semiconductor (CMOS) image sensor is a type of image sensor technology inside Digital Night Vision. It consists of an integrated circuit that records an image. You can think of the image sensor as being similar to the film in an old film camera.
CMOS sensors come in a range of resolutions. Generally the higher the resolution the better image quality that can be presented through the OLED or LCOS display.
1080P is a sensor that has 1920×1080 pixels (width x height)
5MP has 2560×1960 pixels
4K has 3840×2160 pixels
IR WAVE LENGTH (NM)
Digital night vision uses infrared light to reflect off the target. The IR lght type is measured as wavelength (nm). The human eye can see light in the 400nm-700nm range. The most comonly used wavelength in digital night vision is 850NM. This wavelength is easier for CMOS sensors to detect coinjoin’s mixer and provides a better quality image with a longer target range. 850NM illuminators do however cast a faint pink glow from their emitter which some animals, particularly in heavier or regular hunted areas, can detect. This is where the 940NM illuminators can be useful. This wavelength is considered completely invisible to game, but has the trade off of shorter illumination range.
TERMS RELEVANT TO THERMAL:
Thermal imaging works by using infrared sensors to detect differences in temperatures of objects in its line of sight. These sensors can detect heat through rain, fog, snow making their ability to find a target much more powerful than digital night vision and at much longer ranges. The trade off though is the image quality is generally of a much lower resolution than digital night vision.
Sensors are most commmonly found in the resolutions of 320×240, 384×288, 640×480 and 640×512. 1024×768 sensors will soon be available in products from companies such as Sytong. Reolutions lower than the ones listed here are a poor choice for hunting devices.
Sensor pitch measured in microns (µm) is the measurement of the individual pixel size on the sensor. The two most common sensor pitches are 17µm 0.017mm and 12µm 0.012mm. A smaller sensor pitch allows the use of a smaller objective lens to achieve the same field of view.
NETD is an acronym for Nett Equivalent Temperature Difference and is essentially a measurement of sensitivity. This sensitivity is measured in mK (milliKelvin) where one mK is 0.001 degree centigrade. The lower the number the better. Most devices are are <50mk, <35mk, <30mk and <25mk. The norm a couple of years ago would be a sensitivity of <50mk This would include devices from Pard, Guide and Burris. The current norm would be sensors of <35mk. Older technology devices such as Dali can have terrible NETD of <60Mk or even <80Mk. If a device doesn’t specify NETD they are generally trying to hide it.
OBJECTIVE LENSE FOCAL LENGTH
An f‑number (ƒ/#) or f‑stop refers to the ratio of a lens’s focal length to its aperture’s diameter and indicates the amount of light coming through the lens. For thermal infrared cameras, having a lower f‑stop number increases the image contrast and clarity, which results in higher detection distances. When looking at thermal imaging it is very important to look at the lens’s f‑number, as this is often as important the thermal sensor in determining the actual performance of the system.
We’d like to thank the Infiniti Electro Optics for some of the data presented here.