Seek popular science picture frame cutting and digital cutting and optical zoom?

Nowadays, frame cutting is simply a conversion coefficient called frame cutting coefficient, which "equivalently" converts the range of pictures taken by sensors with different sizes into the standard of 35mm film (that is, Quan Huafu). The reason for this is that in the film era, 35mm film is widely used, and people in the industry can basically judge the viewing angles and corresponding imaging characteristics of lenses with different focal lengths in this specification. Gradually, people invisibly convert angle measurement (field of view angle) into linear measurement (lens focal length). In the transition period to the digital age, due to technical and cost problems, the sensor size of the original digital camera is basically smaller than that of 35mm film, so when using the same lens, the picture taken by the digital camera is only equivalent to the central part of the picture taken by the film camera, and the picture range is obviously smaller, so people call this situation frame-changing editing, which probably refers to the central part cut from a complete photo. Later, in order to calculate the lens perspective uniformly, people widely used this so-called cutting factor. Of course, in fact, Quan Huafu is not the largest format specification, so some cropping factors are less than 1. For example, the clipping factor of the frame in 4433 is about 0.8, which has lost its original meaning, just for the convenience of calculating the lens angle.

Digital cutting is basically frame cutting, but sometimes digital cutting is active, that is, for some needs, not all sensors are used, but only some of them are used. Usually, cameras often involve digital cropping when shooting videos. Due to the limitation of picture scale and processing performance, cameras often don't use all sensors when shooting video, which leads to digital cropping. There is also the use of cropping effect to change the perspective. A smaller sensor size can obtain a smaller viewing angle without changing the focal length of the lens. Therefore, sometimes you need to shoot with a telephoto lens in photography, but when you don't have a suitable lens at hand, you can actively abandon some pictures through digital cropping in exchange for an approximate telephoto effect. This is sometimes called extended optical zoom technology. Of course, in essence, digital cutting or extended optical zoom technology does not change the focal length of the lens at all, because the focal length is the physical distance from the optical center of the lens to the imaging plane (now it can be film, CCD or CMOS).

Optical zoom, as mentioned above, the focal length is actually the distance from the optical center of the lens to the imaging plane, so optical zoom is a zoom realized through the optical structure, which is a real focal length change. This is usually achieved by moving some of the shots. Simply put, the larger the optical zoom factor, the farther you can shoot the scene.