Vertical Field of View (VFOV)

The vertical field of view (VFOV) describes the height of the area of a scene that can be observed by the camera. A sensor in rectangular format is most commonly used. For this reason, the height of the sensor together with the focal length of the lens defines the vertical FOV. The horizontal and vertical image angles (width and height of the sensor) determine the total image angle of the camera. These two values result in the diagonal field of view (DFOV). In most cases, the larger side of the rectangular camera is aligned with the horizon, while the vertical FOV is oriented perpendicular to the earth’s surface.

In general, the field of view (FOV) of an instrument is usually described by the angle at which the device is sensitive and can detect the target object. For pyrometers, it is often defined as the measurement spot size of the thermometer. In the field of thermography, the FOV of a camera determines the observable area of a scene that can be imaged by the camera.

The camera FOV is typically expressed in degrees and depends on the configuration of optics and detector size of the thermal imaging camera. The FOV is defined by the ratio of the sensor size and the focal length 𝑓 of the camera optics:

FOV=2∙arctan (sensor size/2f) ≈ sensor size/f

Related to the sensor format, the FOV can be expressed by a horizontal field of view (HFOV) and a vertical field of view (VFOV).

In most cases, the object distance determines the choice of the FOV. For long-range applications, a narrow FOV (TeleOptics) can be selected, which enables the detection of small objects even at long distances. The use of a narrow FOV at a short distance is also possible. The short distance in combination with the narrow FOV leads to a high magnification of the target. For advanced applications, microscope optics are required to enable the detection of small objects with a size of a few micrometers, even when using the 8 µm – 14 µm waveband.

With a wide FOV, the thermal imaging camera can capture a larger area, which can be beneficial for general surveillance and rapid assessment of temperature distribution over wide areas. When inspecting electrical installations such as control cabinets, for example, a wide FOV enables the identification of electrical defects when only confined space is available. Wide-angle optics can also be used for large-scale environmental monitoring, such as fire detection. To detect temperature anomalies, the thermographic image can be analyzed with a hotspot detection algorithm to generate inspection reports or directly trigger a process alarm.

Field of view and optical resolution:

In addition to these FOV definitions, the spatial resolution, the so-called instantaneous field of view (IFOV), must be taken into account to clarify the temperature measurement of small objects. The IFOV represents one pixel of the sensor array and determines the smallest resolvable object size. For accurate temperature measurements, the target size must be larger than the IFOV. The typical size of objects must be at least 3×3 pixels, which defines the measurement field of view (MFOV).

Often the user is interested in a specific distance and wants to know the FOV in mm or m. The FOV calculator allows the user to enter the used camera/optics and displays all necessary FOV data like HFOV, VFOV, IFOV, and MFOV.

The selection of the FOV in thermography cameras is closely linked to the camera’s optical resolution, which refers to its ability to distinguish small details. A camera with high optical resolution (or spatial resolution) can resolve finer details, which is critical when examining small or distant objects. This optical resolution is typically higher in cameras with narrower fields of view. Therefore, the trade-off between FOV and optical resolution is a key consideration in thermography, affecting both the quality and usability of the thermal imaging results produced.