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Monitor camera lens selection

Oct 11, 2017

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Camera lens selection is one of the most important elements of the video surveillance system project. Its quality (index) affects the overall machine index of the camera as well as the quality of the whole project, but also the project cost. Thus, the camera lens in the closed-circuit monitoring system is very important role. Engineering designers and construction workers should always deal with the lens. Designers according to object distance, imaging size calculation lens focal length, construction personnel often on-site debugging, part of the lens is to adjust to the best condition.

 

CCTV camera lens main production

 

Worldwide: Japan, Korea, Germany, China, China Taiwan

China: Fujian, Guangdong, Henan, Gansu, Jilin

Major cities: Fuzhou, Shenzhen, Xiamen, Changchun, Nanyang, Lanzhou, Xinyang

 

At present, CCTV lens world-class brands are basically concentrated in Japan, such as Seiko, Tamron, computar, FUJINON, Tokina, Canon, Avenir Taiwan Asia Optics

 

Some of the domestic lens manufacturers are: Changchun East Asia Optics, Nanyang Wolong Optics, Nanyang Wo Li optical, Fuzhou Che-hung light, Fuzhou Zhengsheng photoelectric equipment, Xiamen Li Ding photoelectric, Fuzhou Feihua photoelectric,

 

At present, the domestic lens needs large lens (C / CS interface) and small lens (M12 interface) accounted for the proportion of 25% and 75%.

 

The proportion of the lens in the cost of the camera is about 20%, is an important part of the camera. With the camera from the high-end to the low end of the complete product chain corresponds to the CCTV lens also formed from the upscale to mid-range to the low range of the complete product chain, the price from tens of dollars to several hundred dollars, a few hundred dollars to a few thousand dollars Should be comprehensive. Profit level is also very different, commonly used single board machine lens, the profit is very low; the higher the technical content, the more advanced the function of the lens, the greater the profits.

 

The lens is equivalent to the human eye lens, if there is no lens, the human eye can not see any objects; if there is no lens, then the camera output image is a vast expanse of white, there is no clear image output, which with our home camera and camera principle Is consistent. When the human eye can not stretch the lens to the normal position, that is, people often say myopia, the front of the scene becomes blurred; camera and lens with a similar phenomenon, when the image becomes unclear , You can adjust the camera's back focus, change the CCD chip and the lens datum of the distance (equivalent to adjust the position of the human eye lens), you can blur the image becomes clear.

 

The lens is the camera's eyes, in order to meet the different monitoring environment and requirements, need to configure different specifications of the lens. Such as the focus of the indoor surveillance, to be clear and large field of view of the image capture, have to configure the wide-angle lens; in the outdoor parking lot, it is necessary to see the whole picture of the parking lot, but also to see the details of the car, this time need to zoom Lens.

 

Camera lens classification

 

Video surveillance system camera lens variety, from the focal length can be divided into short-focus lens, the focus lens, telephoto lens, zoom lens; from the field of view points are wide-angle, standard, vision lens; Lens, manual aperture fixed focus lens, auto iris fixed focus lens, manual zoom lens, auto zoom lens, auto iris electric zoom lens, electric three variable lens and so on.

In the case of

Press the shape function by size according to the size of the sub-press the zoom type by the focal length of a long time points

Spherical lens 1 "25mm auto iris electric zoom long focal length lens

Aspherical lens 1/2 "3mm manual iris manual zoom standard lens

Pinhole lens 1/3 "8.5mm fixed aperture fixed focal length wide-angle lens

Fisheye lens 2/3 "17mm

 

(1) to the lens installation classification: all the camera lens are threaded mouth, CCD camera lens installation has two industry standards, namely, C mount and CS mount. Both threads are the same, but both are different from the lens to the light-sensitive surface. C mount: The distance from the lens mounting datum to the focal point is 17.526mm. CS mounting seat: special C installation, this time should be removed at the front of the camera washer and then install the lens. The distance from the lens mounting datum to the focal point is 12.5mm. C-type cameras can be used CS-type lens, but CS-mounted cameras can not use C-type lens. If you want to mount a C mount lens to a CS mount camera, you need to use the lens converter.

 

(2) to camera lens specifications classification: camera lens specifications should be depending on the camera's CCD size, the two should be corresponding. That is, the camera's CCD target surface size of 1/2 inch, the lens should be selected 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 and camera CCD target surface size does not match, the observation angle will not meet the design requirements, or the screen outside the focus and other issues. 1/2-inch lens can be used for 1/2 inch, 1/3 inch camera; and 1/3 inch lens can only be used for 1/3 inch camera, can not be used for 1/2 inch camera, which is Because the 1/3 inch lens flux is only 1/2 inch lens 44% of the luminous flux, can not meet the 1/2 inch camera luminous flux requirements

 

Fixed aperture lens, the amount of light is fixed. Mainly use the light source or the camera comes with electronic shutter situation.

 

There are two types of auto iris: one is to send a video signal and power from the camera to the lens to control the aperture on the lens, it will be a video signal and power from the camera to the lens to control the lens on the aperture, this video Input lens contains an amplifier circuit, used to convert the video signal from the camera into the control of the aperture motor, known as the video input type Video driver (with Amp); the other is the use of the camera DC voltage directly Control the aperture, which uses the DC voltage on the camera to directly control the aperture, this lens contains only the ammeter-type aperture motor, the camera does not have amplifier circuit, known as the DC input type (DC driverno Amp). Two drive products are not interchangeable, but now there are general-purpose auto iris lens launch.

 

Auto iris lens on the ALC (automatic lens control) adjustment for setting the metering system, the entire screen can be the average brightness, you can also screen the brightest part (peak) to set the reference signal strength, the use of automatic aperture adjustment to use. In general, the ALC has been set at the factory and can be adjusted, but for images that contain a very high brightness target, the image of the bright object may cause a "white level clipping" So that all the screen becomes white, then you can adjust the ALC to transform the screen.

 

In addition, the auto iris lens is equipped with an aperture ring, turn the aperture through the lens, the luminous flux through the lens will change, the luminous flux that is the aperture, generally used F said, the value of the lens focal length and lens diameter ratio, f (focal length) / D (the actual effective aperture of the lens), the smaller the F value, the larger the aperture. The use of auto iris lenses is ideal for the following applications where they can have a wide dynamic range with an auto iris lens in situations such as direct sunlight and other very bright conditions. Requirements in the entire field of view with a good focus, with an auto iris lens than the fixed aperture lens larger depth of field. It is required to use the auto iris lens when the blurring due to the optical signal is minimal on the light.

 

(4) to the size of the lens field of view

 

Standard lens: viewing angle of about 30 degrees, in the 1/2 inch CCD camera, the standard lens focal length is set at 12mm, in the 1/3 inch CCD camera, the standard lens focal length as 8mm.

 

Wide angle lens: 90 degrees above the viewing angle, focal length can be less than a few millimeters, can provide a wider viewing, observation range, near the image distortion

 

Standard lens: viewing angle of about 30 degrees, the use of a wide range

 

Telephoto lens: within 20 degrees of view, the focal length of up to tens of millimeters or hundreds of millimeters, the lens can be in the long-distance situation will be the impact of the object to enlarge, but the observation range becomes smaller

 

Zoom lens (zoom lens): also known as telescopic lens, a manual zoom lens and electric zoom lens two categories.

 

Vari-focus lens: It is between the standard lens and the wide-angle lens, the focal length is continuously variable, you can zoom in the distance object, while providing a wide viewing, so that the scope of monitoring increased. The zoom lens can be set by automatically focusing on both the minimum focal length and the maximum focal length, but the focus from the minimum focal length to the maximum focal length is achieved by manual focus.

 

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

 

Note: three variable lens: adjustable focus, focus, aperture adjustment. Two variable lens: adjustable focal length, focusing focus, auto iris.

 

Common lens angle of view

 

Focal length specification angle

2.1 mm small lens 1/3 150 °

2.5mm small lens 1/3 130 °

2.8mm small lens 1/3 115 °

2.8mm fixed aperture 1/3 115 °

3.6mm 1/3 96 °

4mm 1/3 78 °

6mm 1/3 53 °

8mm 1/3 40 °

12mm 1/3 23 °

16 mm 1/3 17 °

3.5-8mm 1/3 96 ° - 45 °

6-15mm 1/3 54 ° - 23 °

6-36mm electric zoom lens 1/3 51 ° - 9 °

8.5-51mm electric zoom lens 1/57 ° - 10 °

6-60mm electric zoom lens 1/53 ° - 6 °

 

(5) points from the lens focal length

 

Short focal length lens: the wider angle of incidence, can provide a wide field of vision

Medium focal length lens: standard lens, the length of the focal length depending on the size of the CCD

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

Zoom lens: usually electric, can be wide-angle, telephoto changes.

 

The main parameters of the lens

 

Focal length (f, also known as the field of view): focal length is the distance between the lens and the photosensitive element, by changing the lens focal length, you can change the lens magnification, change the size of the captured image. In engineering practice, we often use the horizontal field of view to reflect the shooting range of the screen. The larger the focal length f is, the smaller the viewing angle is, and the smaller the screen range is formed on the photosensitive member. On the other hand, the smaller the focal length f is, the larger the field angle is, and the larger the picture range is formed on the photosensitive member. When the distance between the object and the lens is very far, we can use the following formula: lens magnification focus / material distance. Increase the lens focal length, enlarge the magnification, can be closer to the vision, the scope of the screen is small, the details of the vision to see more clearly; if you reduce the lens focal length, magnification reduced, the scope of the screen expanded, See a bigger scene.

 

Aperture: the aperture installed in the back of the lens, the greater the aperture open, the greater the amount of light through the lens, the higher the clarity of the image; the smaller the aperture, the smaller the amount of light through the lens, the image clarity low. Usually expressed by F (luminous flux). F = focal length (f) / aperture (relative aperture, the relative aperture of the lens is determined by the camera's illuminance, the camera's illumination is proportional to the square of the relative aperture of the lens. In the camera's technical indicators, we can often see 6mm / F1.4 such parameters, which indicates that the focal length of the lens is 6mm, luminous flux of 1.4, then we can easily calculate the aperture of 4.29mm. In the case where the focal length f is the same, the smaller the F value, the larger the aperture, the greater the luminous flux to the CCD chip.

 

Lens and CCD sensor configuration

 

CCD imaging size, that is, the camera screen width and height ratio and the TV screen width and height ratio, usually 4: 3. This ensures that the video image of the camera is not deformed on the display.

 

Lens focal length configuration to determine the appropriate focal length is an important factor in determining image quality. f = v * D / V or f = h * D / H. Where v represents the height of the CCD imaging size, V represents the height of the observed object, h represents the width of the CCD imaging size, H represents the width of the object being observed, and D represents the distance from the object to the lens. Assuming 1/3 "CCD camera observation, the measured object width 500 mm, height 400 mm, the lens focus from the object 5000 mm from the formula can be calculated: focal length f = 4.8 × 5000/500 48 mm or focal length f = 3.6 × 5000/400 45 mm.

 

Note (CCD size):

Specification length and width

1/4 3.6 2.4

1/3 4.8 3.6

1/2 6.4 4.8

2/3 8.8 6.6

3/4 9.6 6.6

1 12.7 9.6

 

Tip: one machine lens multiple calculation: multiple = f maximum / f minimum

For example: 22 times = 85.8 / 3.9 27 times = 94.5 / 3.5

 

Lens focal length and the best exposure distance:

 

For example, assume that with 1/3 "CCD camera observation, the measured object width of 7.2 meters (ten adult men's width, the standard best irradiation width), 5.4 meters high (an adult man appeared on the screen 1/3 height, (1/3 "CCD width size) × 30 / 7.2 = 20mm or focal length f = 3.6 (1/3" CCD height), the focal length of the lens is 30 meters from the object. Size) x 30 / 5.4 = 20 mm.

 

Lens focal length 2.8mm 3.5mm 4mm 4.8mm 6mm 8mm 12mm 16mm 25mm 60mm 73.8mm

Object distance 4.3m 5.4m 6m 7.3m 9m 12m 18m 25m 38m 120m 150m

 

 

Lens use places and angles:

 

1, wide-angle lens: angle of 90 degrees or more, generally used in the elevator car, the hall and other small viewing distance from the perspective of places; such as 2.8MM2.5MM

2, the perspective of more than 60 degrees for 5 * 5 meters or so places 3.6MM4MM

3, the perspective of more than 50 degrees for 8-10 meters around the place 6MM

4, the perspective of more than 40 degrees for 10-18 meters around the place 8MM

5, the perspective of more than 30 degrees for 20-30 meters around the place 12MM16MM

6, the perspective of more than 20 degrees for 30-50 meters or so place 25MM

7, telephoto lens: angle of view within 20 degrees, the focal length range from tens of millimeters to hundreds of millimeters, for long-distance monitoring

8, zoom lens: the focal length of the lens variable, from wide to variable telephoto, for the depth of field, wide viewing angle of the region;

9, pinhole lens: for hidden monitoring.

 

The smaller the lens, the larger the area being monitored, and the relatively small image objects. The larger the lens, the smaller the monitored area (narrow), and the relatively large image object.

Can be a simple calculation method: visual distance ÷ 2 is equivalent to the required lens, and then refer to the perspective.


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