CCTV lens Refers to the lens of a CCTV camera. Since a surveillance camera is just a single video capture device, the resolution of the lens are higher than the camera of a computer. But they cannot higher than a professional digital camera or dv.

In the closed circuit television(CCTV) system, the camera is also called a camera or CCD (Charge Coupled Device), which is a charge coupled device. Strictly speaking, a camera is a general term for a camera and a lens.

The primary sensor component of a camera is a CCD, which has the characteristics of high speed, low distortion, long life, anti-vibration, anti-magnetic field, small size, and no afterimage. CCD is Abbreviation for Charge Couple Device. It can change the gloss into an electric charge and store and transfer the electric charge. It can also take out the stored electric charge to change the voltage, so it is an aspiring imaging element.

Lens view distance

Can objects 100m, 500m and even 1km away be clearly displayed on the monitor. The decisive factor for this problem is generally the focal length of the lens. The longer the focal length, the farther you “see” it, but at the same time the field of view angle becomes smaller, resulting in a narrower viewing range.

For a simple example, if you use a standard lens to just see the basic characteristics of a person (male or female) in the distance. Switching to a long focal length lens may see the facial features (whether there are moles or scars), but I can’t see what trousers and shoes the person is wearing (this part has “spilled out”). But using a wide-angle lens can only see someone in the picture (not even men and women can distinguish), but can see clearly Where is the person in the entire surveillance scene, and what other characters or reference objects are there around?

Therefore, a more scientific statement about “how far to look” should be “the size of the image formed on the screen can correspond to how tall or wide the scene at the actual observation distance”. For example, using an 8mm lens to observe a scene at a distance of 10m, if there are 10 people standing in a row there, it can just fill the entire monitor screen horizontally.

Standard in general

In order to be able to detect targets in the surveillance range more clearly and achieve automatic tracking, it is generally required that targets on the CCD target surface occupy at least three lines of television lines. To be able to distinguish a person, the person’s face imaging should generally be required to occupy more than 12.7mm (0.5in) on a 356mm (14in) monitor.

Lens angle of view

In practical applications, users often ask questions such as how far away the camera can see or how wide the scene can be seen by the camera. This is actually determined by the focal length of the selected lens. The resolution of the selected camera is related to the resolution of the monitor.

The focal length of an optical system refers to the distance from the main point of the light group to the focal point. The focal length of the lens is actually the focal length of the combined light group that constitutes the lens. It determines the size of the captured image. We use a lens with a different focal length to shoot an object at the same position.  The size of the scene captured by the camera with a long focal length lens Large.  On the contrary, the size of the scene captured by the camera with a short focal length lens is small.

Theoretically, any kind of lens can shoot a distant object and form a small image on the imaging target surface of the camera. However, due to the limitation of the pixels, when the imaging is smaller than one pixel of the image sensor, it is small.  An image of the subject can no longer be formed.  And even if the image is a few pixels in size, the image is difficult to discern what is.

How to estimate the required focal length

the first method:

When the size of the subject and the distance from the object to the lens are known, the focal length of the selected lens can be estimated according to the following two formulas:

f = h * D / H

f = v * D / V

f-the focal length of the lens

h, v-horizontal and vertical dimensions of the CCD photosensitive target surface

D——distance from lens center to subject

H, V-horizontal and vertical dimensions of the subject

The second method:

Another monitoring lens focal length estimation method, this only applies to lenses above 4mm. For example: if the focal length (unit mm) of the lens is represented by X.  Then 2 * X is needed to see the details, X is to see the contours.  And X / 2 is to see the approximate movement of the subject. If you choose the distance of the object to be monitored from the surveillance camera is 10 meters.  Choose a 5mm lens to see the main activity.  A  lens that needs about 10mm to see the outline, and a 20mm lens to see the details.

Focal length estimation method (lens above 4mm):

See details = 2 * X Physical features = X Behavioral features = X / 2 (The distance between the lens and the measured object is X meters, and the focal length unit is mm)

Different characteristics of the image presented by lenses with different focal lengths at different distances. In a word, under a certain focal length, the subject farther away will be smaller.  Within a certain distance, the longer the focal length is, the narrower the viewing angle will be.  Aand the more specific the subject will be.

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