How to Choose Lens？
If the camera is a human eye, the lens can be compared to eyeball; it is directly related to overseeing the proximity, scope and effectiveness of objects. The selection should be considered the following points:
1) Lens the size of lens is same or bigger than the size of camera imaging surface. For example: 1 / 3 "camera can choose 1 / 3" - 1 "the whole range of lens, however, the horizontal perspective are same. Only the use of more than 1 / 3 "lens gets better image quality and higher resolution.
2) Selection of the suitable lens; the longer focus length, the greater distance overseen, the smaller the horizontal perspective, the more narrow the scope of the objects; vice verse. Lens focal length can be got according to the following formula.
3) f=A×L/H （f-- lens focus length；A-- the size of camera’s CCD；L-- the distance from the lens and the objects；H-- the height of the objects）
- 1 inch
- 2/3 inch
- 1/2 inch
- 1/3 inch
- 1/4 inch
- CCD the size of the CCD
- 9.6㎜
- 6.6㎜
- 4.8㎜
- 3.6㎜
- 2.7㎜
4) Consider the change of light. The light plays a very important role in image capture. Generally, the light did not change a lot, we often use the manual iris lenses to fix, If the light changed greatly, like outdoor 24-hour supervision, should use auto iris, According to the chiaroscuro of light, it adjusts by itself, and insure image quality. However it should be noted that if light illumination is uneven, particularly, there is great contrast between the monitored goals and the backgrounds’ light, auto lens is not ideal.
5) Considering the best-watched scope. Because the lens focal length and the horizontal perspective are the inverse ratio, if we would like to see far away, and want to see broadly and clearly, this is not possible. Each focal length are only in a certain range to get the best results, If watch the far distances and larger scope, it is best to increase the number of cameras, or use electric zoom lens to equip with platforms’ installation.
6) Lens’ mount should be complied with cameras. The camera and lens are usually CS-type. CS-type camera can match C-type and C-type lens, but with the C-type lens, it should add the distribution ring between them, otherwise, it could damage the protection glass of CCD imaging surface, causing losing. C-type camera cannot match the CS-type.
