How to choose camera cctv lens guide
The image size of the lens can be divided into: 25.4MM（1 IN）16.9mm（2/3 IN）12.7MM(1/2 IN) 8.47MM(1/3 IN) 6.35Mm(1/4 in)
Selecting the cctv lens should make the lens image size is greater than or equal to the camera's target size
|
Ccd sensor size |
25.4 |
16.9 |
12.7 |
8.47 |
6.35 |
|
1 |
2/3 |
1/2 |
1/3 |
1/4 |
|
|
diagonal |
16 |
11 |
8 |
6 |
4.5 |
|
vertical |
9.6 |
6.6 |
4.8 |
3.6 |
2.7 |
|
horizontal |
12.7 |
8.8 |
6.4 |
4.8 |
3.6 |
Lens focal length calculation formula:
f=hD/H f=vD/V
V H is the ccd sensor size, H V is the object size monitored ,D is the distance between the object and the camera.
Horizontal view angle: 2 arctg(h/2f)
vertical view angle:2 arctg(h/2f)
focal length f is shorter, the FOV is bigger, the view distance is shorter .the focal length f is bigger, the field of view angle is smaller, the view distance is longer.
Horizontal field angle of several lenses
|
Size F |
2.8 |
3.5 |
4.0 |
4.8 |
6.0 |
6.8 |
12 |
16 |
25 |
|
1/3 |
86 |
67 |
62 |
52 |
42 |
32 |
22 |
17 |
10 |
|
1/2 |
|
94 |
|
69 |
57 |
42 |
29 |
22 |
14 |
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
Types of lenses (classification according to application)
Wide angle lens: above 90 degrees angle, observation range is bigger, near the image deformation
Standard lens: visual angle of 30 degrees or so, widely used
Long focal lens: under the angle of 20 degrees, the focal length of up to tens or hundreds of mm
Zoom lens: continuously variable focal length of the lens, the focal length can be changed from wide-angle to telephoto
Pinhole lens: used for covert observation, often mounted on a ceiling or wall, etc
Relative aperture
In order to control the flux through the lens , lens aperture are setted.
The smaller the value of F, the larger of the aperture ,the flux reached CCD chip is bigger.So in the case of same focal length , the smaller of the F value, the better of the lens.
Focas Length
1.Fixed focal length: fixed focal length, can be divided into two kinds of aperture and no aperture
With Aperture: the size of the lens aperture can be adjusted.According to the changes of environmental light, the size of the aperture should be adjusted accordingly.Aperture size can be adjusted manually or automatically.Manual adjustment of the aperture, known as the Manual Iris CCTV Lenses; lens comes with a micro motor automatically adjust the aperture, called DC Auto Iris CCTV Lenses.
No aperture: constant aperture, the light is fixed. The main light source constant or camera with electronic shutter.
Zoom lens: the focal length can be adjusted according to the need to enlarge or reduce the image of the object.
Commonly used zoom lens is six times, ten times zoom
Single zoom lens: generally automatic aperture and auto focus lens, and the focal length to be adjusted Manually.
Principles for choosing lenses
The lens has been divided into auto iris and manual iris.auto iris cctv lens is used for illumination changing in more occasions, manual iris cctv lens is for the light of the object light stability.
The cctv lens is installed with C type and CS mount lens m12 lens.C type installation of the lens in the CCD camera and the lens between the multi 5mm adjust the aperture value of the ring
Small tip: camera resolution (line number) Division
About 250 thousand pixels, the color resolution of 330 lines, black and white resolution of about 400 lines
Between 380 thousand and 250 thousand pixels, the color resolution is 420 lines, and the black and white resolution is about 500 lines
More than 380 thousand pixels, the color resolution of 480 lines, black and white resolution of about 600 lines
The key technology and adverse factors of infrared lens camera
The camera uses CCD to sense all the light (visible, infrared and ultraviolet), which is caused the images taken during the day and our naked eye only to observe the visible light produced by the camera is very different. As the CCD sensor is sense infrared, it will interfere with the operation of DSP, resulting in partial color changed.
In order to solve this problem, as long as the CCD does not receive the infrared light can be, so between the lens and CCD with an infrared filter can be solved, its role is to prevent infrared ray to enter the CCD, letting CCD can only response to visible light, allowing the camera to have the image and we see images consistent with our eyes.
Heat dissipation of the camera body itself