Intelligent choice of the camcorder focal length. Six tips

Will expensive network video surveillance equipment be able to solve these problems if using the wrong lenses? Most probably not. The fact is that the overall performance of video monitoring is influenced by all system components, especially the characteristics of the optical device. What is the correct focal length for video monitoring? Let’s figure it out.

Three interconnected equipment parameters

Each camera designed for video monitoring always has three closely interrelated parameters. Namely, we can talk about:

• focal length (abbreviated FL). It is customary to measure it in millimetres (mm). The purpose is to determine the distance from the matrix equipment to its lens;
• matrix size. This parameter is measured in inches and determines the actual size of the image. Experts pay attention to the fact that the lenses are selected to have identical and/or smaller parameters for the cameras. In this case, you need to check the availability of suitable fastening;
• the angle of view (generally accepted measurement in degrees). It defines the surveillance area that the camera can cover. With a wide viewing angle, the focal length of the camcorder will be small.

Video equipment with wide panoramic lenses

A camcorder with a viewing angle of 120 degrees or more is wide panoramic or wide-angle.

Surveillance equipment with wide-angle lenses allows large objects and open spaces monitoring, but with less detail. Small details, such as a person’s face, can be seen from a short distance (usually no further than 3 m from the camera itself).

Narrow-format cameras

Narrow-angle or narrow-format models of video cameras provide detailed objects observation, but at the same time, the total observation area cannot be large. 

In general, we can talk about the following correlations for a detailed image: 

• distance up to 50 provides a viewing angle of 20 degrees;
•  distance from 10 m provides a viewing angle from 60 to 70 degrees. 

As a rule, narrow-format video cameras control cash transactions in shops, restaurants, petrol stations, and banks. Also, similar equipment is installed for video filming near ATMs.

Focal Length Formulas 

The focal length of a camera lens can be calculated using two formulas:

Wherein:

“F” is the subject of focal length calculations;

“H” and “v” – the size of the matrix horizontally and vertically, respectively;

“S” – the actual distance to the object of video surveillance;

“H” and “V” – the exact horizontal and vertical size of the video surveillance object, respectively;

Check the established values ​​of the matrix dimensions in the table:

Illustrative example

Let’s make an example:

It is necessary to observe a specific building.

Its length as a horizontal dimension is 20 m.

The remoteness of the building from the location of the video equipment is 26 meters.

Video camera matrix = 1/3 inch, according to the table, the matrix size will be 4.8 mm.

We use the calculation formula: 4.8 × 26/20 = 6.24.

It is necessary to round up the result obtained (to avoid losing part of the picture). As a result, you need to purchase a 7 mm camcorder.

What to do if you can’t determine the observation area in advance?

What to do when there is no clear understanding of the observation area’s scope, or it changes? We recommend using equipment with a varifocal optical system. Such equipment allows you to adjust the FL manually.

And what to do when there is an operational need to move the object away / closer? Use equipment with a motorized lens.

Besides, it is worth paying attention to a separate category of video cameras “Speed ​​doome”. They are also called speed dome cameras. They allow you to quickly change both the FL and the observation angle (within 360 degrees horizontally and 180 degrees vertically).

You can also think about purchasing video cameras with a corridor observation mode.

The essence of use: the camera is mounted vertically, and its image rotates 90 degrees. Consequently, the operator’s monitor displays a vertical picture with a much larger field of view compared to a conventional camera position.

Six tips from a pro

For the effective operation of the video fixing control system, you must take the following rules into account:

1. Think about the FL at the design stage of the surveillance system. Read the article “Video Surveillance Project Design. Everything you need to know. “
2. It is essential to choose cameras with FL suitable for specific tasks and purposes.
3. Use the mathematical formulas to calculate the FL given above. Average parameters for ordinary objects are 3.6 mm. Use 2.8mm lenses for a wide-angle view.
4. Remember that the higher the CCTV camera lens’s focal length, the narrower the viewing angle. 
5. With the same camera focus, equipment with large matrix parameters will have a large viewing angle. 
6. If you have any difficulties, contact the professionals on the site https://faceter.cam/en.

Conclusion

A right lens is not the one that is the most expensive or has the highest resolution matrix, but the one that is capable of solving specific tasks. For the correct choice of video cameras, superficial knowledge is often not enough. You need to understand the technical terminology and have experience with the equipment. Of course, it is better not to jeopardize the security system’s effectiveness, but to seek help from a specialized company.