Field of View (FOV)

The field of view (FOV) of an instrument refers to the angle at which the device can detect the target object. For pyrometers, the FOV is often described as the measurement spot size of the thermometer. In 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. It’s defined by the ratio of the sensor size and the focal length f of the camera optics:

[math]FOV = 2\cdot arctan(\frac{sensor size}{2f}) \approx \frac{sensor size}{f}[/math].

With the sensor format, the FOV can be expressed as a horizontal field of view (HFOV) and a vertical field of view (VFOV). These two values result in the diagonal of the field of view (DFOV).

The choice of the FOV is often determined by the object’s distance. For long-range applications, a narrow FOV (Tele-Optics) can be selected, enabling the detection of small objects even at long distances. The use of a narrow FOV at a short distance is also possible and results in high magnification of the target. For advanced applications, microscope optics are required to detect small objects, even in the 8 µm – 14 µm waveband.

A wide FOV allows the thermal imaging camera to capture a larger area, which can be beneficial for general surveillance and rapid assessment of temperature distribution over wide areas. For inspections of electrical installations or large-scale environmental monitoring, a wide FOV is advantageous.

In addition to FOV, the spatial resolution, or the instantaneous field of view (IFOV), must be considered for accurate temperature measurements 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. Typically, the size of objects must be at least the equivalent of 3×3 pixels, which defines the measurement field of view (MFOV).

The FOV calculator allows users to enter the camera/optics information and displays necessary FOV data such as 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 can resolve finer details, critical when examining small or distant objects. This optical resolution is typically higher in cameras with narrower fields of view, so the trade-off between FOV and optical resolution is an important consideration in thermography, affecting both the quality and usability of the thermal imaging results.