The basic equipment of each camera is the lens. It is it, that thanks to its complex design, makes the camera records the actual picture. Therefore, the selection of right lens has a significant impact on the effects of image recorded by a camera. As already mentioned, the camera viewing angle depends in fact on the lens and its parameters, and above all on lens focal length . This is a distance between the optical center of lens, in which light is focused, and the converter on which light is incident; assuming that the focus is set to infinity (Fig. 1). This value is given in millimetres.
1 - Lens
2 - Image focus (sensor)
3 - Light beam
4 - Focal length
A beam of light passing through the lens fall on the light-sensitive element, called a sensor. The beam falling on opposite sides of the sensor set the lines that form a viewing angle of the camera (fig. 2). In contrast to photographic technique, where the viewing angle of a camera is defined between the opposite image corners, in industrial television a viewing angle is understood in relation to the width of visual field.
1 - Recorded image. Dotted line represents the camera's visual field.
2 - Camera viewing angle (horizontal)
3 - Lens
4 - Focal length
5 - Sensor's diagonal
Thus, as shown on picture, viewing angle (2) in industrial camera depends not only on the distance of lens from the sensor, i.e. focal length (4), but also on the size of a sensor itself (5) on which light is incident. In case of a focal length the greater it is, the smaller is camera's viewing angle. As regards the converter, the bigger light-sensitive element is used, the higher viewing angle will be. One should note, however, that each lens is designed for the specific size of the sensor. Therefore, the same lens in different cameras may have a different viewing angle.
Below, for comparison, an image from APTI-27V2-2812 camera with a viewing angle of 94° (Fig. 3), and the image from M5-V1 camera with a viewing angle up to 150° (Fig. 4).
Fig. 3. Screenshot of APTI-27V2-2812 camera
Fig. 4. Screenshot of M5-V1 camera
The first image is a screenshot of a camera of frequently met viewing angle. One can see a curvature on both the upper beam and on the floor boards, which of course are even. The image is close to natural. A screenshot of the second camera shows an image that is admittedly unnatural (fisheye effect), however, it gives a wide viewing angle, going beyond the scale of the test room. The cameras with a wide viewing angle are a good alternative to rotating cameras, due to a wide visual field.
As it can be seen, there is a close relationship between a viewing angle and a focal length of the lens, sensor size and other not described parameters. When choosing a CCTV camera one should determine: at what height it will be installed and how wide range of vision it should have. There are formulas, tables and calculators, which are helpful in selecting the proper camera. However, to facilitate, in Delta's offer all the cameras and lenses have been tested and their parameters posted on the website of a given product. In addition, our employees based on the basic data such as the place of installation of the camera and width of vision, are willing to help in selecting the equipment.