Which FOCUS to choose for CCTV camera

Focal length of CCTV cameras

In the description of video cameras, you can see such an important parameter as the Focal Length. What does it affect? Let’s understand in this article. Focal length of CCTV camera directly affects the angle of view of the video camera. At the same time it depends on the format of the matrix of the video camera. And to determine the right parameters, you need to take into account some rules. For example:

The longer the focal length of the CCTV camera lens, the narrower the angle of view will be.

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With the same focal length of the video camera the unit with larger sensor size will have a wider angle of view.

In short, the focal length of the CCTV camera is a key parameter in calculating the monitored area. Completely simple calculations help to determine the exact area that will be in the camera’s field of vision. In order to monitor a large area requires a camera with a much wider angle of view than when controlling a long non-broad corridor.

That is, on how much more or less distant the observed objects, depends on the selection of focusing distance CCTV camera. And the more accurate that choice, the more objects will be in the frame. So before you buy a camcorder, you need to pay attention to the settings and parameters, especially the viewing angle, which is dependent on the range of the monitored area.

What is Focus Lens?

Focus is a figure for surveillance camera lenses, which is defined in mm, representing the distance between the matrix and the lens to which the Focus images are held. The most popular index, among the focus of the camera is a figure of 4 mm, which is equal to a review of 70 degrees in the horizontal plane. It is similar to human vision. the same field of view we see. A camera with this lens is the optimal solution for installing surveillance systems in a typical building.

When choosing a lens, you need to keep in mind that the smaller the number of millimeters in the specifications of a surveillance camera, the greater the viewing area will be able to guarantee such equipment. For example, surveillance cameras with a Focus of 2.8 allows you to use the equipment in houses and parks, where you need a wide view.

That said, there are models that have a long focal length. it’s from 6 to 12 mm, which can’t guarantee a large coverage of the area. This would be a great choice for tasks where you need high resolution, for example in financial institutions or stores over the cash register to monitor a small area but guarantee maximum focus.

The angle of view will indicate how wide an area can be covered by the video lens. For example wide angle lens allows to see wide area, but doesn’t provide much sharpness. And low Focus models, allow you to view individual objects.

Choose a lens for your surveillance camera

Any, even the smallest video surveillance system component plays a very important role and in this article we would like to draw your attention to camera lenses. rather neglected, but very important element, without which the work of any camera is unthinkable.

Choosing the lens for your camcorder is based on the tasks for which your system is designed. Correct task definition means the right choice of lens, and this, in turn, will allow you to see on the monitor exactly the image that you want to get, plus will save a considerable amount of time and money that may be needed to select the lens. Remember that a good lens can improve the video image quality of an inexpensive camera and vice versa a low-quality optics can spoil the impression of the most expensive device.

So, what is the first thing to look at when buying a lens. Of course, one of the most important parameters is the focal length, which determines how far and wide your camcorder can see.

Lens focal length is measured in millimeters and is the distance from the focal point of the lens to the video matrix that the resulting image is focused on.

The most common value of focal length in video surveillance is the value of 3.6 mm, which is approximately equal to a 72° horizontal viewing angle and 90° diagonal, which is a close number to the angle of view of the average human eye. Lenses with a focal length of 3.6mm is a great solution for surveillance in small homes or offices.

When choosing a focal length, you should also keep in mind that the smaller the focal length, the less farsighted your camcorder will be. but it will cover a larger area of view. Conversely, the longer the focal length of the lens, the more detailed the video will be, but the area will be covered less. In fact, there’s no concept of worse or better. Simply wide-angle lenses are suitable for a general overview (eg protected area of the yard or parking lot), and a longer focal length allows you to see a more detailed image, which is required at the cash register in supermarkets or banks.

The angle of view value tells you how much of the area your lens can cover when shooting video. If you hear the term “wide angle,” it usually refers to lenses with focal lengths from 3.6 mm and smaller. Wide angle lenses allow you to see more of the area you are looking at, but with less detail. A wide angle lens is very useful for a general overview of a room measuring 20×20 meters, but if you want to see and make a face or record a large sum of money you will need a lens with a longer focal length, such as 16mm.

There are three basic types of surveillance camera lenses. Monofocal (fixed, static), varifocal (varifocal) and zoom (transfocal) lenses.

Monofocal (fixed, static) lenses have one fixed focal length: 2.8 mm, 3.6 mm, 12 mm, etc.п. These lenses do not allow you to adjust the angle of view of the camera or to produce a mechanical focus on the object surveillance. The advantage of this type of lenses is their low cost and ease of installation.

Varofocal lenses (varifocal) lenses allow you to adjust the focal length of the lens, which means you can change the angle of view of the video camera. Varifocal lenses are identified by a range of magnifications, e.g. 2.8. 12 mm, 3.5. 8 mm. The undoubted advantage of these lenses is their versatility, but they are much more expensive than monofocal lenses. In addition, when installing will need to manually adjust the angle of view and point to the Focus of the object or the area you intend to view. Adjustment is done once and only changes if you need to change the angle of view.

Zoom (transfocal) lenses are the most expensive, but they allow you to adjust not only the camera angles, but also to scale the selected area. Basically, these types of lenses are used in PTZ-robotic camcorders, in which the focus positioning, viewing angle and focal length are controlled remotely by the remote control.

A parameter that allows you to adjust the amount of light that the lens transmits to the image sensor. In low-cost models of cameras, the aperture value is in a fixed position, as they are not designed for video recording on objects with sharp variations in light levels, such as in an office or apartment, the light is always about the same level.

Automatic iris allows you to adjust the amount of light hitting the matrix, depending on the light level, this action is performed by a special motor, which is attached to the lens or integrated into the control board of the camcorder. This solution is undoubtedly more expensive, but allows you to get the same good image, regardless of the light level. These lenses are mainly used for outdoor surveillance or at sites with variable illumination.

If you are familiar with the characteristics of video cameras, you can not fail to notice such a value as the size of the video matrix chip, it is usually measured in inches and has the following parameters: 2/3″, 1/2″, 1/3″ or 1/4″. The size of this chip affects the coverage of the monitored area. For example, a 2/3″ sensor sees more than a 1/3″ one, therefore you have to choose the lens according to these features (all lens manufacturers indicate the sensor size for which a certain lens model fits). Keep in mind that lenses for bigger sensor size will work for cameras with smaller sensors, i.e. a lens for a camera with 2/3″ sensor will work for a camera with 2/3″, 1/2″, 1/3″ or 1/4″ sensors, but not vice versa!

To begin with, let’s understand what constitutes an IP video surveillance camera and how it works.

IP camera is equipped with RJ45 network interface for connection to local network or global internet. Feature of the current generation of IP video surveillance cameras is to broadcast video signals and power (PoE technology) over a single twisted-pair cable.

The network cameras are equipped with a high-speed processor and memory unit for: OS, image enhancement functions, analytics functions, security functions. Extensive functionality and flexibility of settings of the IP camera allows you to build a surveillance system to user requirements.

The camera can be optionally equipped with a micro SD memory card slot with 32Gb, 64Gb, 128Gb capacity, to which data is saved according to selected conditions (detection-based, time-based, permanent recording).

Uniqueness of network video cameras is the wireless connection to the Internet. WI-FI is required in CCTV applications where network cabling is impossible.

Connection to IP camera is possible locally through IP recorder or remotely from your PC, smartphone, laptop, tablet. Pre-installed application for Android, Windows Phone, Windows, iPhone, iPad allows you to see the object online, view the archive, and set up recording on a remote server.

Lens type

Fixed (monofocal) lens. The easiest and most inexpensive. Its focal length is fixed and cannot be changed.

In varifocal (variofocal) lenses, you can change the focal length. It is set manually, usually once when the camera is installed at the scene, and thereafter. as needed.

Transfactor or zoom lenses also provide the ability to change the focal length, but remotely, at any time. Changing the focal length is electrically operated, so they are also called motorized lenses.

“A fisheye or panoramic lens is a lens that lets you mount just one camera and still achieve a 360° field of view.

Of course, as a result, the resulting image has the effect of a “bubble”. Straight lines are crooked, but in most cases cameras with these lenses can split a single panoramic image into several individual images, correcting them to what the human eye is accustomed to see.

Pinhole lenses allow for discreet surveillance due to their miniature size. In fact, pinhole camera has no lens, but only a tiny hole instead of a lens. In Ukraine, the use of CCTV is seriously limited, as is the sale of devices for it.

These are the most common types of lens. But going deeper, lenses are also divided up by other parameters:

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What is the focal length of the lens?

Focal length lenses are measured in millimeters, and represents the distance from the lens to the camera matrix, which focuses the image.

The most popular value of focal length on a camcorder is 4 mm. which is approximately equal to a 70° horizontal field of view, which is close to the angle of view of the human eye. Cameras with such a lens, are a universal solution for installing video surveillance systems in typical areas.

So when choosing a lens keep in mind that the smaller the focal length of the lens (e.g. 2.8 mm) the larger the field of view it will cover. Such wide angle lenses are suitable for general view e.g. on parking lots or driveways.

Selection tips

The choice of the angle of view is determined by the task of the camera. If you need to monitor a large area, without singling out a specific object, the device is suitable with a 2.8-3.6 mm lens. The optimum angle is considered to be in the range from 70 to 140 °.

Angle of 60° is close to the angle of view of the human eye. This value is considered a medium. Devices can give a detailed picture at the location of the object at a distance of up to 10 meters.

Long focal length lens with a field of view up to 30° suitable for observing objects that are 20-70 m away from the control room.

Knowing the size of the matrix, calculate the FTR of the lens using the following formulas:

How to choose the lens for your camcorder?

When choosing a camera for video surveillance system, be sure to pay attention to its lens, the main characteristic of which is considered the focal length, which directly affects the viewing angle and clarity of the image obtained. The focal length can be fixed (monofocal lens) or variable (varifocal lens).

  • Monofocal lenses have several modifications. 2.8, 3.6, 4.0, 6.0, 10.0 mm. The most common and convenient one is the monofocal 3.6 mm, it has good sensitivity and is able to distinguish objects clearly at distances of up to 4.5-5 meters and from a distance of 2 meters this camera will give a nearly perfect picture. Monofocal cameras are best used for indoor and around-the-house surveillance, as well as for recognizing visitors at the entrance to buildings.
  • Varifocal lenses also have a wide range of sizes, with the most popular being the 2.8-12.0 mm and 5.0-50.0 mm. Cameras with these lenses give a detailed picture of objects from a distance of 15-50 meters.

If you are planning to buy video surveillance cameras, keep in mind a number of regularities that will facilitate your choice of a suitable model.

  • First, the focal length value is approximately the distance from which you are able to recognize someone you know. With a focal length of, for example, 3.6mm, you’ll be able to identify someone you know from a distance of about 3.6 meters.
  • Secondly, the focal length is roughly half the distance to the person you want to look at in detail. That is, with a lens of 3.6 mm, you will be able to see a stranger in detail at a distance of 1.8-2 meters.

As for the angle of view, remember that the human eye can see the situation at an angle of 60-70 degrees. Wide angle lenses can see almost a full panorama (100. 180 degrees), but have a weak detail of small objects and have the effect of “removing” the object. “Narrow-angle” (up to 50 degrees) are able to see only a small part of the territory in front of them, but provide a clear image of the smallest details and the “zoom” effect of the object.

To ensure that your choice of surveillance camera was reasonable and you are not confused by the characteristics of the focal length and viewing angle, study the information of the parameters:

Lenses for CCTV cameras in our online store

When choosing a lens for CCTV cameras, an important detail is that by choosing a cheap lens from an unknown manufacturer, you run the risk of encountering problems and instead of saving money on repairs.

Optimal would be considered the choice of a medium-sized manufacturer that can supply you with the entire system. Then you won’t need to worry about how to combine all the devices, because the experts will select the best option for you.

In the catalog of lenses you will find a wide range of models from different manufacturers. Bourne Saint-Petersburg specialists will help you with your choice and answer all your questions.

The viewing angle of the camera is the main criterion, which affects the monitored area of the object.

However, this parameter is influenced not only by the focal length, but also by the size of the video camera matrix.

There are several rules to follow when determining the parameter:

  • The longer the focal length of the CCTV camera, the narrower the viewing angle;
  • If the focal length of the video camera is equal, the device with the larger matrix will have a greater angle of view.

The choice of static focus lens depends on the specific situation and the objectives of the video surveillance system. If you want to monitor a long narrow room, for example, a corridor, there is no need to choose a wide lens. Wide panoramic cameras are recommended for monitoring open spaces, where the cost of such a lens can be compensated by using fewer cameras.

  • Large-format, having a viewing angle of 100 ° or more will be able to give a total picture, where the recognition of human faces can be realized from a distance of not more than 3m. They are recommended for intrusion control and perimeter surveillance;
  • Narrow-format, having an angle of about 20°, can transmit a detailed image suitable for detection from 20-50m.
  • Most cameras have a view angle of 60-70 °, which allows for effective video surveillance with guaranteed identification of an object with 10m. However, the transmitted image quality may be insufficient for automatic identification by special software.

All data provided is based on a 1-2Mpic sensor

Most beginners who want to install video surveillance system make the system mistake of believing that if you take a camera with a high-resolution sensor, then using a widescreen lens you can cover a large area and get a quality picture suitable for future use. This is only partially true. Experienced professionals generally use undocumented rules derived empirically:

  • Recognition of a familiar person in a video image occurs from a distance equal to the focal length. This means a camera with a fixed 9mm lens will identify the stranger from a real distance of 9. 10m.
  • To get a good quality image that allows you to identify a stranger (usually for law enforcement) is only possible from a distance equal to half the focal length. In our case, it will not be more than 4.5-5 m.

Adjust the lens focus according to the following rules: