Thermal imaging technology in a nutshell

The ABCs of thermal imaging – everything you need to know.

Whether for locating a downed target, fawn rescue, or reliable game identification – a thermal imaging camera has become an indispensable piece of hunting equipment. Do you know what you should look out for when making a purchase, or can’t really figure it out from the technical data sheet? Learn everything you need to know about thermal imaging cameras and clip-ons here – from how they work, to the most important components, to practical tips on how to find the perfect thermal imaging device for you. 

How does a thermal
imaging camera work?

How does a thermal
imaging camera work?

Even in complete darkness, all objects emit thermal radiation. Thermal radiation is light in the long-wave infrared range, which is invisible to the human eye. It is precisely this long-wave infrared radiation that a thermal imaging camera uses to generate an image.

How does a thermal imaging camera work?

  • Thermal radiation travels through high-quality germanium lenses onto the sensor
    Thermal imaging devices capture long-wave infrared light in the mid-infrared range between 8 and 13 µm wavelength. This long-wave infrared radiation cannot be transmitted through normal glass. For this reason, thermal imaging cameras require lenses made of special material, such as germanium, which allows long-wave thermal radiation to pass through..
  • The sensor (microbolometer) converts the thermal radiation into electrical signals
    In the process, a value is assigned to each pixel.
  • The processor creates a colored representation of the temperature of the object
    To do this, the processor uses an image processing algorithm – at ZEISS we have ZSIP Pro for this purpose, which reproduces the temperature of the object as a high-contrast image on the display based on the signals from the individual pixels. The greater the temperature differences between the body and the environment, the higher the contrast of the image..
  • The image shown on the viewfinder display can be viewed through the eyepiece
    In this process, each temperature value is assigned to a specific color and shown on the display.

What are the components of
a thermal imaging camera?

What are the components of
a thermal imaging camera?

When looking for the right thermal imaging device, it is important to pay attention to the components’ various characteristics and properties. Simply comparing individual parameters is not a reliable way of assessing the performance of thermal imaging technology. This means it always comes down to how the individual components interact with each other. When evaluating thermal imaging devices, the following components play a particularly important role:

1. Front lens and internal lens

High-quality germanium lenses enable long-wave thermal radiation to be projected onto an image sensor. When using a thermal imaging camera to look through a window or at a person wearing glasses, it becomes apparent that conventional glass does not transmit long-wave thermal radiation.

Depending on how and where you plan to use the thermal imaging device, larger or smaller focal lengths may be more suitable. Thermal imaging devices with smaller focal lengths usually have a shorter range, but a larger field of view and a greater depth of field, i.e., a larger distance that is sharply imaged. They are particularly suitable for hunting in forested areas and provide a good overview. A thermal imaging device with a long focal length stands out due to its long range and is suitable for hunting in the open field, making it possible to accurately identify small details at long distances.

Depending on the intended use case, you need to either decide on a focal length or choose a thermal imaging camera that features an interchangeable lens.

2. Pixel pitch and sensor size

How does a microbolometer (sensor) work?
The microbolometer is the heart of the thermal imaging camera, so to speak. The thermal sensor converts heat radiation into electrical signals.

1. Heat radiation strikes an individual pixel.
2. It is absorbed by a specially manufactured, extremely thin membrane
3. This membrane heats up due to the heat radiation
4. When the temperature of the absorber changes, its electrical resistance also changes
5. The resistivity is measured and used to generate the image.


What does pixel pitch mean?
The number of pixels corresponds to the number of detector cells. If, for example, a device is indicated as having a pixel resolution of 640 x 480, as is the case with the ZEISS DTI 6, this means that the detector has 640 pixels along the horizontal axis and 480 pixels along the vertical axis. The higher the number, the sharper the image and the better the zoom quality you can expect.

Pixel pitch refers to the distance between the centers of two pixels on a microbolometer.
A smaller pixel pitch means that each pixel is smaller. A small pixel pitch is not always a benefit, however. To achieve ideal imaging results, the optical components need to be adapted to the pixel pitch. Reducing the pixel pitch, for example, results in a smaller field of view, provided all other components remain the same. Increasing the number of pixels results in a higher resolution while maintaining the large field of view. If the optical components aren’t modified, the image quality may be worse even with a smaller pixel pitch. So it all comes down to ensuring that the components are perfectly compatible.

3. Image processing

The image processing algorithm analyzes and processes the thermal images from the microbolometer.

For this purpose, the algorithm breaks down the image into individual pixels and optimizes the image in terms of brightness, contrast, noise, and edge sharpness. In this context, precision and speed play the decisive role when it comes to processing images quickly and without artifacts.

ZEISS’s proprietary ZSIP Pro algorithm precisely optimizes these images in three stages:

  1. Unwanted noise is removed from the sensor’s output signal.
  2. The image is divided into sections that are individually optimized with respect to contrast and then adjusted to match each other.
  3. The sharpness of the image areas with heat sources is optimized in order to obtain an optimal image with clearly defined boundaries between the game and its surroundings..

This optimization also compensates for the temperature difference between the cold sky and the relatively warm forest when observing game. This results in detailed images that make it possible to accurately identify targets.

4. Display

In an LCoS (liquid crystal on silicon) display, light is reflected off of a thin layer of liquid crystals. This results in a particularly uniform image. An AMOLED (active-matrix organic light-emitting diode) display forms the image thanks to its light-emitting diodes and, compared to an LCoS display, offers a fluid and particularly high-contrast viewing experience thanks to its extremely low latency, even during rapid panning movements. However, the same applies in this case: the perfect compatibility of the components makes all the difference. An extremely high-resolution display with a small sensor size wouldn’t make sense.

5. Eyepiece

To create an immersive viewing experience, even for people who wear glasses, the eyepiece must be perfectly tailored to the display resolution.

What other technical
data is relevant?

What other technical
data is relevant?

In addition to the sensor size, pixel pitch, and display resolution, the technical data sheet also lists other important specifications. Do you know which ones to pay attention to and how to tell them apart? Learn about all the key specs here. That way, you’ll know exactly what to look for when purchasing your next thermal imaging camera.

Field of view (FoV)

What is the field of view?
The field of view of a thermal imaging device (often abbreviated FoV) describes the size of the visible angle when looking through the device. In most cases, the field of view is expressed in meters per 100 meters. The larger the field of view, the wider the image, but the smaller the details. Conversely, the smaller the field of view, the narrower the image, but the greater the magnification of the details. As such, the field of view also determines the thermal imaging camera’s ideal use case – devices with a larger FOV provide a perfect overview when hunting in forested areas or while searching for previously downed game. A smaller FOV offers more range and is ideal for hunting in the open field, as it allows game to be reliably identified over longer distances. Our range of thermal imaging products includes devices with both large and small fields of view.

Optical magnification (digital zoom)

What level of zoom makes sense?
In the case of digital zoom, unlike zoom via the focal length, the image is enlarged by multiplying the pixels. The larger the sensor, the more detailed the image, and the better the zoom. This means that it all depends on the relationship between the resolution and the sensor. The DTI 3, for example, has four zoom levels that are perfectly matched to the resolution and the 17-micron pixel pitch sensor to deliver detailed images. With its higher resolution of 640 x 480 and a pixel pitch of 12 microns, the DTI 6 even offers a 10-step digital zoom that makes specific details visible even at the highest level of magnification.

Frame rate

What does frame rate mean?
The frame rate is indicated in Hertz (Hz) and describes how often the thermal imaging camera processes, optimizes, and updates an image per second. The higher the frame rate, the better the image when viewed in motion. To ensure a smooth image, the frame rate shouldn’t be lower than 25 Hz. All of our thermal imaging devices feature a frame rate of 50 Hz, delivering a high-contrast, wobble-free, optimal image with no lag for reliable game identification during night hunting.

NETD

What is NETD?
The detector sensitivity, also referred to as noise equivalent temperature difference (NETD), describes the temperature sensitivity of a thermal imaging camera. It is expressed in millikelvin (mK) and represents the smallest temperature difference that a thermal imaging device can detect. The lower the NETD value, the higher the sensitivity. The following scale can be used to classify NETD values:

  • <40 mK (Excellent)
  • <50 mK (Good)
  • <60 mK (Acceptable)
  • <80 mK (Satisfactory)
The ZEISS thermal imaging devices all have a NETD value <40mK and can therefore be rated as excellent. However, for the overall evaluation of the imaging performance of a thermal imaging device, the interaction of all components is crucial. At ZEISS, this is ensured by the ZSIP, which guarantees a particularly detailed image. While the NETD value is thus an important value when it comes to evaluating the quality of a thermal imaging device, it shouldn’t be viewed as a sole and isolated criterion when selecting a thermal imaging camera.

Aperture (f-number)

What is the aperture?
The aperture value or f-number indicates the ratio of the focal length to the diameter of a thermal imaging camera’s entrance pupil. The smaller this number, the larger the diameter of the lens, the more infrared radiation enters the device, and the higher the contrast and sharpness of the image.
Further questions about thermal imaging:

Why do you need a thermal imaging camera?

Thermal imaging camera to locate a target after a shot
A thermal imaging camera obviously can’t replace a bloodhound, but it can usually be used to detect the still warm body of a downed target extremely well, even if the animal slipped into a thicket. In this way, you can search large areas for the game you’ve downed in the shortest possible time. In some cases, a thermal imaging camera even detects the still-warm sweat marks directly after the shot, making it easier to find the direction of escape.

Thermal imaging camera for fawn rescue
The first mowing of the meadows puts many fawns and young hares at risk of dying from being mowed over. With the help of thermal imaging devices, large areas can be scanned for heat sources in a very short time. In this context, even the slightest gaps in the tall grass are enough to spot the game. The most effective way of searching is from the air using a thermal imaging camera attached to a drone.

Thermal imaging devices for game monitoring
Due to being disturbed by humans during daytime, many game species shift their activities to the evening or night hours. When using a thermal imaging camera for the first time, hunters are often surprised at how much game is actually in their hunting ground. With the help of thermal imaging cameras, it is possible to gather valuable information about the respective game species, for example when counting hares.

Thermal imaging devices to combat ASF and damage caused by game
Due to the increasing wild boar population, the agricultural landscape is struggling to deal with massive amounts of damage caused by game. The monthly full moon phases are no longer sufficient to contain the population and the damage. In addition, the spread of African swine fever (ASF) requires the increased management of the wild boar population in the event of an epidemic. This is where thermal imaging cameras can help hunters hunt more effectively regardless of the time of day, as the game can be quickly located and reliably identified.

Thermal imaging devices for detection and precise identification
Unambiguously identifying game at dusk or at night poses significant challenges to hunters. A thermal imaging camera can help in this regard. With its detailed images, it makes it possible to reliably identify the animal, i.e., whether it is a boar or a sow. ZEISS thermal imaging devices can be used to localize game over long distances, for example when hunting sows at night, so that hunters can come down from their raised hides early enough to stalk the herd.

What role does ergonomics play when it comes to thermal imaging devices?

ZEISS thermal imaging cameras and clip-ons were developed by hunters for hunters. It is important to be particularly quiet when hunting, especially at night. This is precisely what the intuitive and ergonomic ErgoControl operating concept makes possible, which all ZEISS thermal imagers have in common – the optimally shaped buttons can be operated silently, even in cold conditions and with gloves on. Thanks to their intelligent positioning, each button can be controlled quickly, quietly, and precisely – whether with the left or the right hand.

When does thermal imaging make sense and when is night vision more appropriate? 

 

 Thermal imaging technology
 Night vision technology

Funktionsweise

A thermal imaging camera uses an infrared sensor to convert thermal radiation from bodies or objects into images. In this case, the image reproduces the outlines, but not the original colors. It does not require residual light to display an image. The higher the temperature difference between body and the surroundings, the clearer the image.

In contrast to thermal imaging devices, night-vision devices work by amplifying the residual light. To do this, they use a photocathode that captures light consisting of photons, converts it into electrons, and amplifies it through electronic and chemical processes. The electrons are converted into visible light on the phosphor screen, which the hunters then perceive in green-tinted or black and white images. Night-vision devices only work when residual light is available. Otherwise, they require external light sources that either scare away game if the wrong wavelength is selected, or are often prohibited in conjunction with night-vision clip-ons (infrared emitters).

Advantages
  • Rapid localization
  • Long range
  • Can be used during the day and night
  • Do not require additional light sources
  • Largely unaffected by weather conditions
  • Very low power consumption
  • Produce extremely detailed images at short distances

Disadvantages
  • Distances are difficult to estimate
  • Can't be used through car windows
  • Limited range and localization remains difficult
  • Limited lifetime due to design
  • Can only be used at night and with residual light
  • Heavy weight

Which color mode for which application?
Black-Hot

In Black-Hot mode, the warm areas are displayed in black and the colder areas in white. This makes the outlines of the game more visible, which is why this mode is suitable for detecting and identifying.

White-Hot

In White-Hot mode, warm areas are displayed in white and the colder areas in black or gray. Due to the strong contrast, the game can be located more quickly and reliably identified in this mode.

Red-Hot

In Red-Hot mode, heat sources are displayed in shades of red, making it possible to quickly detect game, especially on warmer days or in densely overgrown forest areas.

Rainbow

In Rainbow mode, heat sources are displayed in the colors of the rainbow. This makes it possible to clearly detect even the smallest temperature differences. The ZEISS DTI 6 thermal imaging cameras also feature the Universal, Fog, Detect, and Identify image modes, which allow hunters to quickly and perfectly adjust the image to the situation at hand.

Developed by hunters for hunters – the stories behind ZEISS thermal imaging devices
Marc's story

Why a reliable app is important

Stefan's story

Which tests our products have to withstand

Tammo's story

Why ergonomics matters so much

louhunting's story

Why she relies on ZEISS products

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