1. What is focal length?
Refers to the distance from the center of the lens to the focal point of the light concentration when the directional light is incidence. In simple terms, focal length is the distance between the focal point and the center point of the mask.
2. Classification of focal length
The unit of focal length, the focal length is measured in "mm". The more common focal lengths are: 8mm, 12mm, 16mm, 25mm, 35mm, 50mm, 75mm, etc., and the focal length is also divided into fixed focus and zoom. Generally, the focal length of the lens will be marked on the lens, such as 50mm, or 9-50mm, etc. If there is only one number marked on the lens, it means that the lens is a prime lens, such as a 50mm lens, which means that the lens can only shoot at a fixed 50mm focal length, and it is a lens with a fixed focal length. We call this a prime lens.
If there are two numbers marked on the lens, it means that the lens is a zoom lens, such as a 9-50mm lens, which means that the focal length of the lens can be adjusted between 9-50mm.
3. The difference in focal length
The smaller the focal length and the wider the framing range, the wider the field of view of the picture, and the more scenes can be captured, but the smaller the scenery will be in the frame. The larger the focal length and the narrower the framing range, the smaller the field of view and the fewer scenes you can capture, but the scenery accounts for a large proportion of the frame.
In the following picture, you can see that different focal lengths correspond to different viewing angles, and if you need more viewing angles, then you need more different focal lengths.
In the image below, it is clear that as the focal length of the lens increases, the field of view becomes smaller and smaller, and the number of images that can be captured by the camera becomes smaller and smaller, but the scene that is photographed becomes larger.
4. So how to choose the focal length
The choice depends on the application, and in summary, a shorter focal length will make your subjects appear smaller, while a longer focal length will make them magnify. A shorter focal length also means you have a wider field of view, while a longer focal length makes it narrower.
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Qiheng Optics provides a variety of high-performance, high-transmittance SWIR lenses, telephoto fog-transmitting lenses, continuous zoom lenses, industrial FA lenses, and customized lenses.
In our product library, you can find the right lens for most market applications. The following shows some of the footage introduction, please consult the staff for more needs.
SWIR shortwave infrared prime lens.
SWIR SWIR continuous zoom lens.
Telephoto fog-penetrating lens.
Continuous zoom lens.
Industrial FA lenses.
Custom-made lenses.