Basic knowledge of camera lens

Basic knowledge of lens focal length of digital camera

Digital cameras, like human eyes, capture everything in the world through the lens. If the human eye has an error (myopia) in the focal length, it can't distinguish things correctly. As the lens of a digital camera, its most important characteristic is also the focal length of the lens. The focal length of the lens is different, the breadth of the scene that can be shot is different, and the photo effect is also very different. If you often use an ordinary 35 mm camera, you should have a basic understanding of the lens focal length of the camera. For example, you usually take scenery and commemorative photos with a lens of about 35 mm, and take photos with a lens of about 80 mm to identify the "big head" you need. Compared with traditional cameras, because digital cameras use CCD photosensitive devices, the focal lengths indicated on their lenses are usually 5.0 mm, 10 mm, etc. In ordinary 35 mm cameras, super wide-angle or fisheye lens is generally used, while the lens commonly used by digital camera manufacturers is only a small wide-angle lens equivalent to 35 mm cameras.

It is not difficult to see that for the same imaging area, the shorter the focal length of the lens, the larger the viewing angle; For a lens with the same focal length, the smaller the imaging area, the smaller the viewing angle of the lens. The imaging area of 35mm camera is equal to the photosensitive area of 135 film-the standard 36× 24mm. Digital cameras use CCD sensor to replace the position of film in traditional cameras, but its area has several specifications, ranging from 18.4× 27.6mm for high-grade professional cameras to 2/3, 1/2 and 6556 for ordinary digital cameras. In other words, the same lens has a wide-angle effect on some digital cameras, but it may become a standard lens on other cameras. It seems inconvenient for us to distinguish the visual angle of digital camera lens by focal length value, so digital camera manufacturers usually provide a relatively easy-to-compare value, that is, mark the focal length of 35 mm camera lens with the same visual angle as digital camera lens, so that we can easily understand the corresponding focal length value. A lens like Fuji MX-500 has a focal length of 7.6 mm and a diagonal viewing angle of 70 degrees, which is equivalent to a 35 mm lens and is a small wide angle. Fuji's MX-600 is equipped with a small wide-angle zoom lens equivalent to 35- 105 mm. When evaluating and purchasing digital cameras, we only need to refer to the lens focal length converted into 35mm cameras. What is the actual focal length of the lens is basically irrelevant to us, and you can't calculate it in detail. In fact, the optical zoom factor of digital camera can basically reflect this index. Although there will be some differences between different types of digital cameras, the differences will not be too great. If you don't deliberately pursue a specific focal length equivalent to a 35mm camera, refer to the optical zoom multiple of a digital camera.

Maybe some users still don't know the actual focal length of the digital camera lens, because if it is 7.6 mm focal length on a 35 mm camera, it is an extremely rare fisheye lens, it must be huge and expensive, and the photos taken are seriously distorted and have a strong sense of perspective. But the 7.6 mm lens on the digital camera is the size of a thumb, and the whole digital camera is much cheaper than the traditional lens. Although only a small piece in the middle is used for imaging, the exaggerated fisheye effect makes people feel drums about its image quality. In fact, this kind of worry is unnecessary. The lens diameter of 35mm camera is very large to ensure the imaging quality around the picture, while the area of CCD is much smaller than that of film. To achieve high-quality imaging in a small area, only a small lens size is enough. Moreover, what actually determines the lens structure is its effective viewing angle, not the simple focal length value. The 7.6 mm lens on digital camera adopts the design of 35 mm small wide-angle lens on traditional camera, instead of the structure of 7.6 mm fisheye lens. Therefore, the focal length of digital camera lens is not directly related to the actual imaging effect. Because the volume of the lens is small, the relative cost is also reduced, but higher imaging quality can be easily realized.