Which lens to choose for a surveillance camera?
It all depends on the goals that the camera installs, if you need to see a distant or well-enlarged object, it is better to use the lens with the greatest focal length (detailed examination of faces, consideration of the face value of banknotes), if you need to cover the largest possible area, then you need to use the lens with the smallest focal length. Keep in mind that the larger the focal length of the lens, the smaller the camera’s viewing angle and the wider the camera’s viewing angle, the less detailed the image.
Usually, the best option is to use varifocal lenses (with variable focus), so you can adjust the image to your needs directly at the installation site. This will allow you to change focus from 2.8 to 50 mm.
Many of our customers ask for cameras with a standard fixed wide-angle lens with a focal length of 3.6 mm. Cameras with such a lens are designed for installation in a corner and provide a viewing angle of 72 degrees, as well as provide effective surveillance in the area of 10x10 meters. If you need to adjust the viewing angle and you are not sure whether a camera with a fixed lens will allow you to cover all the necessary area or give an image with the required detail, we recommend using cameras with a variable focal (varifocal) lens.
| Focal length | Field of view | |||||||||||
| Distance 1.5 м. | Distance 3 м. | Distance 5 м. | Distance 7.5 м. | Distance 15 м. | Distance 30 м. | |||||||
| mm | H | W | H | W | H | W | H | W | H | W | H | W |
| 3.6 | 2.5 | 1.5 | 4.5 | 3 | 7 | 4.5 | 11.5 | 8 | 23 | 16 | 46 | 31.5 |
| 6.0 | 1.3 | 1 | 2.5 | 2 | 3.5 | 2.8 | 5.8 | 4.5 | 12 | 9 | 23.5 | 17.5 |
| 8.0 | 1 | 0.5 | 2 | 1.2 | 3 | 2 | 4.5 | 3.4 | 9 | 6.5 | 17.5 | 13 |
| 12.0 | 0.5 | 0.5 | 1.2 | 1 | 2 | 1.3 | 3 | 2.2 | 6 | 4.5 | 12 | 9 |
The viewing angle of cameras depending on the lens, in meters in height and width.
Lux gradation depending on the light, Lux table.
| Condition | Illumination in Lux | |
| Direct sunlight | 100,000 | Daylight |
| Sunny day | 10,000 | |
| Cloudy day | 1,000 | |
| Very cloudy day | 100 | |
| Twilight | 10 | |
| Deeptwilight | 1 | |
| Full moon | 0.1 | Low illumination |
| A quarter of a moon | 0.01 | |
| Starlight | 0.0011 | |
| Clear night | 0.000 | |
During the day, the image produced by the camcorder may vary depending on the atmospheric conditions of the day and the general level of lighting. Direct sunlight increases the contrast level of the image, which makes the image clearer, but due to different levels of illumination, for example, one part of the image is darkened and the other is lit by bright sunlight, the overall image quality may fall, this problem is solved using cameras with a wide dynamic range (WDR).
On a cloudy or cloudy day, the camera’s matrix receives less light, which may result in noise, some of the image will become difficult to see. To obtain the optimal image of the camera with variable illumination (for example, when using cameras on the street), the cameras use auto iris and adjust to the light level in order to get the best picture for a given level of illumination. Typically, illumination is measured in Luxes and can range from 100,000 to 0.0001, which exceeds the capabilities of most cameras, for areas with poor lighting, it is best to use photosensitive Low Lux cameras. The graph on the right summarizes the lighting data and shows which lighting corresponds to a certain value.