1. What is the focal length?
We all know that the imaging principle of camera is pinhole imaging, so in a digital camera, the focal length refers to the distance from the lens pinhole to the sensor, and the unit is mm (millimeter).
2. Definition of Different Lens Types
When it comes to camera lenses, some people may know that there are fixed-focus lenses and zoom lenses. A fixed focal length lens means that the focal length is fixed, while a zoom lens means that the focal length of the lens is variable.
Generally, the focal length will be marked on the camera lens, such as 50mm, 24-70mm, etc. If there is only one number on the lens, it means that it is a fixed-focus lens, such as a 50mm lens, which means that the lens can only be fixed at a focal length of 50mm.
If there are two numbers marked on the lens, it means that it is a zoom lens, such as a 24-70mm lens, which means that the focal length of this lens can be adjusted freely between 24-70mm.
So does the variable focal length have any influence on our photography process?
3. The relationship between focal length and lens
For example, we need to change the size of the target in the picture during the shooting process. Using a fixed-focus lens requires the photographer to move his position back and forth; while using a zoom lens only requires us to change the focal length of the camera.
4. The Differences in Focal Length
The smaller the focal length is, the wider the viewfinder range gets, and the wider the field of view of the captured picture will be. So more scenes can be captured, but the scene is very small in the picture.
The larger the focal length is, the narrower the viewfinder range gets, and the smaller the field of view of the captured picture will be. So fewer scenes can be captured, but the proportion of the scene in the picture is very large.
Infrared camera modules developed by GSTiR team offer wide variety of lens types, such as fixed focus lens, zoom lens, motorized lens etc.
Let's take the infrared thermal image below as an example to understand the difference:
In this thermal image, as the focal length decreases, the field of view of thermal image becomes larger and larger, and more scenes can be captured by the infrared camera, but the target being captured will become smaller.