Life through the lens.

Life through the lens.

A modern video camera designed for CCTV has a set of many important characteristics and functional capabilities. But their implementation depends entirely on how correctly the lens is selected and configured.
The lens of a video camera is often compared to the eyes of the system, and despite the somewhat cliched nature of the metaphor, it is essentially very true. After all, as is well known, the human eye collects information (light), which is transmitted to the retina, where the light is converted into signals transmitted to the brain. The brain, in turn, converts the received signals into an image visible to the human eye.
Just like the human eye, the lens collects information (light) about surrounding objects. This information is transmitted through the lens to the focal point, where the light is focused on the camera matrix. The matrix converts the light into an electrical signal for the camera electronics, which forms the image.
The angle of view of a lens is directly related to the focal length of the lens. A short focal length gives a wide angle of view. As the focal length increases, the angle of view of the camera narrows. In science, there is such a thing as a normal angle of view. This angle is about 35, which corresponds to the angle of view of the human eye.
Focal length, which is measured in millimeters, is the distance from the optical center of the lens to the surface of the matrix.

Classification
In general, mass-produced goods, and there are hundreds of different lenses for video surveillance systems alone, are usually classified, naturally, based on certain features.
By aperture type, lenses are divided into two main groups: with manual and automatic aperture.
Lenses with manual diaphragm are used, for example, if the room where the video surveillance system is installed has constant lighting. This could be a 24-hour supermarket. By adjusting the diaphragm, we regulate the amount of light that passes through the lens to the video camera matrix, and thus obtain an optimal picture in terms of illumination.
The automatic diaphragm of the lens is controlled by a signal coming from the camera. That is, the camera itself processes the signal coming from the matrix, evaluates the amount of light and sends a command to the lens, according to which the required degree of diaphragm opening is set.
Lenses with automatic diaphragm, in turn, are divided into two types: with direct drive (DC drive) and video drive (Video drive). Both automatically adjust to changing lighting conditions, so they are mainly used outdoors.
In the first case, the diaphragm motor is controlled directly by the voltage coming from the camera. Depending on this signal, the motor operates to open or close the diaphragm. That is, the camera controls the amount of light transmitted through the lens. It is the camera that tells the lens how much light it needs. The popularity of lenses with a direct auto diaphragm drive is due to the fact that they require almost no adjustment. Some manufacturers supply such lenses with a pre-soldered auto diaphragm drive connector.
In the second case, the signal processing module is located in the lens itself. The lens receives a video signal from the camera, and the module evaluates this signal and makes a decision on the appropriate actions regarding closing or opening the aperture.
These lenses differ in cost — lenses with a video drive are somewhat more expensive. At the same time, lenses with a video drive are practically no longer in demand in most countries. The market for this equipment has survived only in Russia and the CIS countries.
Two more large groups: with a fixed focal length and variable focal length.
Fixed focal length lenses are cheaper, but when using them, you need to accurately calculate the required angle of view, that is, the angle at which the lens will look. This determines what space the camera will capture and what the operator will see on the monitor. In this case, it is impossible to zoom in on the object of observation; the only available function is to adjust the focus. The range of application of such lenses is limited, — they are usually used in cameras that monitor entrances to objects.

Varifocal lenses can be adjusted on the spot to accommodate specific needs. Also, if the direction the camera is facing changes, you can change the settings without changing the lens itself.
Lenses with IR correction should also be highlighted. The use of these lenses allows you to avoid defocusing when the illumination changes, when the spectrum of light passing through the lens shifts to the infrared region. This effect occurs due to the fact that at different times of the day, the light passing through the lens has a different wavelength, and the refractive index of different wavelengths varies. If you configure the lens for daytime operation, then by evening the image may be blurry, out of focus. In this case, the system operation service staff will be forced to adjust the focus of the lens twice a day. Lenses with IR correction have a special glass composition and/or a special coating on the glass, which almost completely compensate for the defocusing effect. Such lenses are most often used with day/night cameras. And if the system is installed outdoors with IR illumination, then the use of lenses with IR correction is a mandatory requirement.

Zoom lenses
These are varifocal lenses, in which the lens system is designed in such a way that focusing occurs automatically, you only need to initially adjust the lens focus. Inside the zoom lens, groups of lenses move in relation to each other in such a way that when changing the scale, the image is always in focus. Zoom lenses can be with manual adjustment and motorized. Zoom lenses with manual adjustment are usually used when it is not possible to place the camera close to the object, but there is no need to adjust the focal length in them. It is enough to adjust the lens to the minimum angle once to be able to observe a distant object in detail from afar. They can also be used for various tests and demonstrations.
Motorized zoom lenses can be controlled and adjusted remotely. Zoom lenses are used when you need to observe a distant object: zoom in, examine some details. The most convenient zoom lenses are those that have all the motors and presets. Especially if the camera is used on a rotary device, also with presets — then you can preset the system to certain positions in which the camera will automatically become, and the lens will be adjusted in a given way. Let's say a rotation to a certain angle in a horizontal or vertical plane is programmed, and the zoom lens performs a preset zoom in or out, focus and aperture settings.
Of course, it is best if the zoom lens has three motors that control zoom, focus and aperture. But there are models with fewer motors: with two, for example, to control only zoom and focus. Zoom lenses are present in the product lines of all leading lens manufacturers. You can get acquainted with some models in the review part of the publication.

The horizontal angle of view is 55 , — this value is greater than the angle that conventional lenses can provide. The DF003 lens provides high resolution with 18x magnification.

DF003 Lens for 1/3 Megapixel Cameras (Tamron)
The model has an F/1.6 aperture and a focal length of 4.7 to 84.6 mm. The use of aspherical elements allows for excellent lens performance, both in terms of accuracy and quality throughout the entire zoom range. The lens has a day/night mode switching function. The DF003 lens has an ergonomic design. Only environmentally friendly materials are used in its production.

D32x10R4D-V41 (Fujinon)
The world's first zoom lens for megapixel CCTV cameras with IR correction (works in day and night modes without focus «swimming»). In addition, the lens supports the preset function. That is, if you connect it to a control keyboard that allows you to «remember» the nodal angles of the CCTV trajectory, then it is possible to automatically, without operator intervention, repeat the «drive» along a given trajectory.

The zoom lens has a 32x optical zoom for instant detailed identification of remote objects, stable image sharpness both in the dark and in excess illumination (thanks to IR correction). D32x10R4D-V41 provides operational video monitoring of the most important areas of the protected territory using presets.
The electromechanical part of this zoom lens includes three independent servo drives consisting of a potentiometer and a DC motor, which allow the operator to adjust the optical zoom, aperture, and set the camera focus independently of each other. The use of DC motors in the zoom lens design ensures a soft and quick start of all controlled units of the structure and smooth regulation of their movement speed over a wide range.

55x Zoom Lens Series TM55Z1038 (TOKINA)
A series of 4 models of 55x zoom lenses TM55Z1038 (focal length 10-550mm F/3.8). Two models in this series are equipped with a built-in 2x extender, which increases the focal length at a teleangle to 1100mm. The lens is suitable for all video cameras with a C and CS mount, a matrix format of 1/2 and smaller. At a teleangle with a 1/3 format camera and a distance to the object of 550m, you can fit a human figure of 180cm in height in full screen. The TM55Z1038 series is indispensable when observing such large-scale objects as state borders, coastlines, airport and seaport territories, highways and railways, oil plantations and pipelines. The TM55Z1038 series is represented by the following models:

TM55Z1038AIPN：ｆ=10-550mm F/3.8 Video Iris with Focus/Zoom Pre-set; TM55Z1038AIPNX2：ｆ=10-550(-1100)mm F/3.8 Video Iris with Focus/Zoom Pre-set・2X extender; TM55Z1038NPN：ｆ=10-550mm F/3.8 Motorized Iris with Focus/Zoom/Iris Pre-set; TM55Z1038NPNX2：ｆ=10-550(-1100)mm F/3.8 Motorized Iris with Focus/Zoom/Iris Pre-set・2X extender.

55x 2-motor ZOOM lens with auto diaphragm, potentiometer, remote diaphragm control and built-in electric extender (Pentax)
H55ZME-5F (ZF) (code C61233ZF), ¼” format, C mount, focal length 12.0 — 660.0 mm, aperture 4 — 1500, VS aperture control, horizontal angle of view 31 ° 39 — 0 ° 34, 105 mm thread.
With extender, magnification 2.0, focal length 24.0 — 1320.0 mm, aperture 8 — 3000, horizontal angle of view 15 ° 28 — 1500, — 0°17′.
When using the built-in extender, the maximum focal length is 1320 mm. It is ideal for monitoring borders, coastlines, video surveillance in city centers and squares. Thanks to the use of special glass, the images are clear and high-contrast across the entire focal length range. With a maximum aperture of F1500 (F3000 when using the extender), the H55ZME-5F (ZF) lens (code C61233ZF) is especially effective for use with cameras operating in low light conditions.