Theory behind the practical use
As follow you can find all information about the thermal imaging technology, frequently asked questions and the most important terms and perfomance indicators.
Thermal Imgaging Theory
In the past, optics with light intensifiers were primarily used in the night vision technology field. Now thermal imaging optics are taking over the market. But how do they work?
There are a few decisive performance features that need to be taken into account when describing and classifying imaging devices.
Non-cooled imaging devices detect long-wavelength infrared light, i.e. wavelengths between 8 and 13µm, and therefore use the temperature radiation of bodies. Each body with a temperature of >0 Kelvin = -273°C generates this infrared radiation. For instance, an ice cube also has a heat radiation that can be measured. This radiation, also known as electromagnetic waves, is made visible using the thermal imaging detector. Today, these imaging devices are also able to measure temperature differences of under 0.05°C. They therefore display energy beams of the infrared light on the screen. The function is completely independent of visible light conditions. The warmer a body, the better it can be detected and made visible. Heat sources are recognised quickly with these optics and ‘shine’ clearly in the dark. Additional IR light sources, like for instance in light intensifiers, are no longer necessary. 150 years ago, the two scientists Stefan and Boltzmann discovered the law of nature that all bodies emit energy in the shape of light waves. Only a few animals, for instance some snakes and insects (mosquitos), can perceive this radiation directly. The brightness of the radiated infrared light depends heavily on the temperature.
What are the benefits of a thermal imaging camera compared to a light intensifier?
Frequently asked questions
This grahic shows the working-lightwavelength relation of the specific detector type.
- NVG (Night Vision Googles)
- CMOS (Complementary Metal Oxide Semiconductor)
- CCD (Charged Coupled Device)
- SWIR (Short Wave Infrared)
- MWIR (Medium Wave Infrared)
- LWIR (Long Wave Infrared)
More details can be found in our blog.
Ensure that the lens has an image frequency of at least 25 Hz. Think about the field of vision you require because the size of the lens has a huge impact on the price. If possible, try out the lenses on your shortlist in practice, because just comparing the performance data and the cheaper price can be very disappointing. The guarantee time should be at least 3 years.
160x120 pixels are sufficient for close-range, up to 100m with a low sharpness of detail. 320x240 pixels are recommended for a medium distance up to 600m with good detail recognition. You will require a resolution of 640x480 pixels for good detail recognition and greater distances up to 1,200m. Don’t forget the zoom aspect when selecting the resolution you require. A 4x zoom only makes sense from a resolution of 640x480 pixels upwards.
A digital zoom enlarges the image by increasing the number of pixels. This means that with a 4x zoom and a detector resolution of 384x240 pixels the detail only has an effective presentation of 96x72 pixels. A 4x zoom only makes sense when the resolution is 640x480 pixels or higher.
The size of the lens, stated by the f-number, should be selected based on the main application purpose. The larger the lens, the better the image quality, the higher the range, but the field of vision is smaller.
9 Hz is adequate for a pure tripod-based or static viewing. We recommend at least 25 Hz for hunting. You will only notice the difference between 30 Hz and 50 Hz if the optics are moved quickly.
At least an image frequency of 25 Hz, a resolution of 320x240 pixels and a 19mm lens.
Absolutely. State-of-the-art in the non-cooled imaging devices are VOx detectors with a detector cell size of 12 micrometre squared. The advantages are obvious: Smaller design, smaller lenses with the same field of vision compared to detectors with a larger pitch, lighter, less power consumption and in particular, sharper and more detailed image presentation thanks to the use of modern image optimisation software.
Binocular lenses allow stereoscopic viewing; i.e. images are given depth. Binocular lenses are more suitable for viewing over long distances.
Black/white is sufficient, because heat sources can be recognised more easily and quickly.
- is a thermal sensor used to detect electromagnetic radia-tion, and medium and long-wave infrared. As a two-dimensional Focal Plane Array (detector cells arranged in a grid of cells), it represents the image sensor of the thermal imaging cameras.
- Spectral Response
- The spectral range states the wavelength that the light needs to have so that the detector can detect the light. The larger the range, the more clear and differentiated the image.
- Number of detector cells. A detector with a resolution of 640x480 pixels has 640 image points in the horizontal direction times 480 picture points in the vertical direction. This corresponds to a detector number of 307,200 image points, i.e. 0.3 megapixels. The higher the number, the sharper the image; a higher zoom factor is more beneficial.
- Detector cell size in micrometres squared (µm); in the case of detectors with a resolution of 320x240 pixels this usually 25µm or 17µm. The state of the art for a resolution of 640x480 pixels is usually 12µm. The smaller the pitch number, the smaller the devices and objectives can be built.
- Hertz (Hz)
- Image repetition frequency in Hertz. The higher the Hz number, the smoother moving images are.
- stands for Field of View and is usually stated in width x height at 100m or an angle value (angle starting from the lens). The smaller the FOV, the more restricted the FOV close up.
- stands for Noise Equivalent Temperature Difference and describes a performance indicator for measuring temperature stability and is the decisive performance indicator for assessing the performance capability of a detector. It is stated in milli-Kelvin (mK). The smaller this performance indicator, the greater the contrast of the image.
- The f-number states the ratio of the focal length (lens clearance to the detector) to the diameter of the effective entrance pupil. The smaller the f-number, the larger the diameter of the lens, the more light incidence, the greater the contrast and sharpness of the image.
- stands for the detector carrier material amorphous silicon. It has a high electromagnetic wave absorption capacity in the optical and near-infrared spectral range. It is less expensive to manufacture, but has a few disadvantages in terms of image quality compared to VOx detectors.
- stands for the detector carrier material vanadium oxide and is a chemical compound with high electrical conductivity and is a better technical variant than ASi detectors.
- stands for Liquid Crystal on Silicon and describes a display with liquid crystals for presentation of images.
- OLED / AMOLED
- stands for Organic Light Emitting Diode or Active Matrix Organic Light Emitting Diode and describes display with light diodes for presentation of images. Compared to LCoS displays, they have a higher contrast and faster response time when presenting images.
- Stands for Video Graphics Array and describes a computer graphic standard. A VGA-typical image resolution is 640x480 pixels.
- NUC Calibration
- Stands for Non Uniformity Correction and describes the calibration of the sensitivity of the individual pixels, so that points with the same temperature in the picture appear equally bright. Calibration is automatic by means of a shutter and a click can usually be heard in most devices. In some devices, calibration can/must be carried out manually. Instead of a shutter, the lens can also be covered manually.
- Most lenses allow presentation of the image sources in white, black, red or rainbow colours.