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Recycling the type of scrapped camera

Whether the objects of the scrapped camera are 100m, 500m or even 1km away can be clearly displayed on the monitor. The determinant of this problem is, in general, the focal length of the lens. The longer the focal length, the farther the "look" is, but at the same time the angle of view becomes smaller, and the range of viewing becomes narrower.

There are many types of lenses, each of which has its own characteristics. Depending on the function and structure, the price of these lenses is very different. For example, the power zoom lens is about 10 times higher than the price of a normal fixed-focus lens. Therefore, the lens can be selected more flexibly only if the characteristics of various lenses are correctly understood.

A, fixed aperture fixed focus lens

Fixed-aperture fixed-focus lens is a relatively simple type of lens. There is only one manually adjustable focus adjustment ring (the ring is marked with a number of distance reference values). Rotating the ring left and right can make it on the CCD target surface. The image is the clearest, and the image on the monitor screen is also the clearest.

Since it is a fixed aperture lens, there is no aperture adjustment ring on the lens, which means that the aperture of the lens is not adjustable, so the luminous flux entering the lens cannot be changed by simply changing the lens factor, but can only be changed by the change. The illuminance of the scene is adjusted, such as increasing or decreasing the lighting of the scene. This type of lens is generally used in applications where the illuminance is relatively uniform, such as indoor lighting throughout the day, in other occasions, it is required to be used with CCD cameras with automatic electronic shutter function (of course, most of the current market) CCD cameras are equipped with an automatic electronic shutter function) that simulates changes in luminous flux through adjustment of the electronic shutter.


B, manual aperture fixed focus lens

The manual aperture fixed focus lens has a larger aperture adjustment ring than the fixed aperture fixed focus lens. The aperture adjustment range can generally be adjusted from F1. 2 or F1. 4 to fully closed, which can easily adapt to the illumination of the scene. However, due to the aperture The adjustment is manually performed manually. Once the camera is installed, the position is fixed, and it is not so easy to adjust the aperture frequently. Therefore, the lens is generally applied to the occasion where the illumination is relatively uniform, and in other occasions. It needs to be used with a CCD camera with automatic electronic shutter function. For example, in the morning and evening, when there is a large change in illuminance such as noon, sunny day and cloudy day, the change of the optical flux is simulated by the adjustment of the electronic shutter.


C, automatic aperture fixed focus lens

The auto-iris fixed-focus lens has a relatively large change in structure. It is equivalent to adding a micro-motor driven by a gear mesh to the aperture adjustment ring of the manual aperture fixed-focus lens, and extracting 3 cores or 4 from its drive circuit. The core wire is sent to the auto iris lens, so that the micro motor in the lens rotates in the forward or reverse direction, thereby the size of the high speed aperture. The auto iris lens is divided into two types: amplifier (video driven) and amplifierless (DC driven).


D, manual zoom lens

As the name implies, the focal length of the manual zoom lens is variable. It has a focal length adjustment ring that can adjust the focal length of the lens within a certain range. The ratio is generally 2 to 3 times, and the focal length is generally 3. 6 to 8 mm. In practical engineering applications, by manually adjusting the lens's zoom ring, you can easily select the field of view of the surveillance site, such as: you can choose to monitor the entire room or choose to monitor a local area of ​​the room. When it is not well understood about the environmental conditions of the surveillance site, it is obviously very important to use such a lens.

For most TV monitoring system projects, it is very inconvenient to manually zoom after the camera is installed. Therefore, after the project is completed, the focal length of the manual zoom lens is rarely adjusted. To the role of the fixed focus lens. Therefore, the manual zoom lens is generally used in a situation where the demand is relatively strict and the fixed focus lens is not easy to meet the requirements. However, this type of lens is favored by engineers because it is used in the construction and debugging process. By adjusting the focal length within a certain range, it is generally possible to find a viewing range that can satisfy the user (without repeatedly changing the lens with different focal lengths). ), this is particularly convenient in field construction.


E, auto iris electric zoom lens

This type of lens additionally adds two micro motors to the aforementioned auto-iris fixed-focus lens, one of which is engaged with the zoom ring of the lens, and can change the focal length of the lens when it is controlled to rotate; the other motor Engages with the focus ring of the lens, and the focus of the lens is achieved when it is controlled to rotate. Since the lens adds two functions that can be adjusted remotely, this type of lens is also called an electric two-variable lens.

The auto-iris motorized zoom lens generally leads to two sets of multi-core wires, one of which is an auto-iris control line, the principle and connection of which are exactly the same as those of the aforementioned auto-iris fixed-focus lens; the other is to control the lens zoom and focus. The control line is generally connected to the pan/tilt lens controller and decoder. When operating the zoom or focus button of the remote control indoor pan/tilt lens controller and decoder, a positive or negative DC voltage will be applied to the zoom or focus control line, which is applied to the corresponding micro motor. , to complete the zoom and focus adjustment function of the lens.

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(1) Classification by camera lens specifications

The camera lens specifications should be based on the CCD size of the camera, and the two should correspond. That is, when the CCD target size of the camera is 1/2 inch, the lens should be 1/2 inch.

When the CCD target size of the camera is 1/3 inch, the lens should be 1/3 inch.

When the CCD target size of the camera is 1/4 inch, the lens should be 1/4 inch.

If the lens size does not match the size of the camera's CCD target surface, the viewing angle will not meet the design requirements, or the screen will be out of focus.


(2) Classification by lens aperture

The lens has a manual iris and an auto iris. It is used with the camera. The manual iris lens is suitable for applications with constant brightness. The aperture of the auto iris lens is automatically adjusted when the brightness is changed. When the brightness changes. There are two types of automatic iris lenses: one is to send a video signal and power from the camera to the lens to control the aperture on the lens, called the video input type, and the other is to use the DC voltage on the camera to directly control the aperture. It is a DC input type.

The ALC (Automatic Lens Control) adjustment on the auto iris lens is used to set the metering system, and the reference signal strength can be set and supplied by the average brightness of the entire screen or the brightest part (peak) in the picture;

Automatic aperture adjustment is used. In general, the ALC has been set at the factory and can be adjusted. However , when a scene with a very high brightness is included in the scene, the image of the bright object may cause “white level clipping”. Make all screens white, and you can adjust ALC to change the picture . In addition, the auto iris lens is equipped with an aperture ring. When the aperture ring is rotated, the luminous flux passing through the lens changes.

The luminous flux, that is, the aperture, is generally expressed by F, which is the ratio of the focal length of the lens to the aperture of the lens, ie: F

=f (focal length) / D (actual effective aperture of the lens), the smaller the F value, the larger the aperture.

With an auto iris lens, it is ideal for the following applications: they can have a wide dynamic range with an auto iris lens in very bright situations such as direct sunlight.

An automatic aperture lens is required to have a larger depth of field than a fixed aperture lens when there is good focus throughout the field of view. An auto iris lens should be used when the blur caused by the light signal is minimized on the light.


(3) Classification by the field of view of the lens

The standard lens of the surveillance camera: the viewing angle is about 30 degrees. In the 1/2-inch CCD camera, the standard lens focal length is set to 12mm. In the 1/3-inch CCD camera, the standard lens focal length is set to 8mm.

Wide-angle lens: The viewing angle is more than 90 degrees, and the focal length can be less than a few millimeters, providing a wide viewing angle.

Telephoto lens: The angle of view is less than 20 degrees, and the focal length can reach several meters or even tens of meters. This lens can enlarge the influence of the captured object at a long distance, but make the observation range smaller.

Zoom lens: Also known as a zoom lens, there are two types of manual zoom lenses and electric zoom lenses.

Variable focus lens (vari-focus lens): It is between the standard lens and the wide-angle lens. The focal length is continuously variable, which can amplify distant objects and provide a wide viewing angle to increase the monitoring range. The zoom lens can be set to automatically focus on the minimum focal length and maximum focal length, but the focus from the minimum focal length to the maximum focal length is achieved by manual focusing.

Pinhole lens: The lens is a few millimeters in diameter and can be concealed.


(4) From the focal length of the lens

Short focal length lens: Provides a wide field of view due to the wide angle of incidence.

Medium focal length lens: Standard lens, the length of the focal length depends on the size of the CCD.

Long focal length lens: Due to the narrow angle of incidence, it can only provide a narrow view and is suitable for long-distance monitoring.

Zoom lens: Usually electric, it can be used for wide angle, standard or far vision lenses.

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