Understand the basic knowledge of lens

[Key words]: the focal length of the focal length lens determines the viewing angle range of the lens. The longer the focal length is, the smaller the viewing angle is. The shorter the focal length is, the larger the viewing angle is. < / P > < p > APS-C frame camera needs to be multiplied by a conversion coefficient when calculating the lens focal length. The coefficient of Nikon camera is 1.5, and that of Canon camera is 1.6. In other words, APS-C frame camera is more advantageous than full frame camera in the long focus end. < / P > < p > [Key words]: aperture aperture is a very important component in the lens, which is composed of many metal sheets. The metal sheet can move. By changing its opening degree, the amount of light entering the lens can be controlled. At the same time, it is also an important factor in shooting beautiful virtual background. < / P > < p > all kinds of aperture that can be used in a camera are limited by the performance of the lens, that is, if the maximum aperture of the lens is f3.5, then it is impossible for the camera to use a larger aperture to shoot. It is not difficult to see how important an excellent lens is to the camera and even the photographer. < / P > < p > the size of the aperture is expressed by the aperture value. The smaller the value is, the larger the aperture is opened and the more light flux is; the larger the value is, the smaller the aperture is opened and the less light flux is. We often say that the large and small aperture refers to the aperture rather than the aperture value. < / P > < p > the so-called constant aperture refers to having the same aperture in any focal section of the lens. For the fixed focus lens, because its focal length is fixed, its aperture is also constant. Therefore, the constant aperture is more important for the zoom lens. For example, AF-S 24-70mm f2.8g, one of Nikon’s mirror kings, has a large aperture of constant f2.8. It can have a large aperture of f2.8 at any focal length between 24-70mm, so as to ensure sufficient light input or better virtual effect. For example, when the aperture of the lens is changed to fs-1055.6 mm, the focal length of the lens will automatically change to fs-1056.5 mm. < / P > < p > [Key words]: Motor refers to the device used to push the lens for automatic focusing. In short, it can be divided into ordinary motor and ultrasonic motor. < / P > < p > the focusing performance of ordinary motor is relatively general, which usually appears on the low-end lens. It is mainly aimed at the camera without motor, such as Nikon D3100 and d5100. This kind of camera must use the lens with motor to realize automatic focusing, otherwise it can only focus manually. < / P > < p > the ultrasonic motor can make the focusing fast and quiet, and can focus manually all the time. In Nikon, Canon and other original manufacturers, this technology is gradually being popularized in all kinds of lenses, while the use of ultrasonic motor in auxiliary lens is less. < / P > < p > [Key words]: internal focusing, whose English full name is internal focusing, abbreviated as if, refers to internal focusing technology. When the lens is in focus, the length of the lens is kept constant. < / P > < p > the adoption of if technology makes fast and quiet focusing possible, simplifies the lens structure, so that the volume and weight of the lens are greatly reduced. Even some ultra telephoto lenses may be hand-held for shooting, and focusing is faster and easier. The internal focusing system can also shorten the nearest shooting distance of the lens, and improve the imaging quality of the telephoto lens in close shooting. < / P > < p > in addition, the lens with if technology will not rotate when focusing, so it is very convenient to use the filter, especially the polarizer or gradient lens with direction limitation. < / P > < p > [Key words]: the working principle of anti shake is to detect the camera’s own vibration through the bracket installed on the photosensitive element. On the basis of detecting the direction, speed and movement of the vibration, the displacement of the photosensitive element that can be vibrated is calculated, and then the vibration of the camera is compensated to reduce the blurring degree of the photo. < p > < p > at present, the shooting speed of the shutter is lower than 4, which can ensure the clear shooting results. For example, when shooting with a 200 mm focal length, the safety shutter should be 1 / 200 S. after the anti shake function is turned on, the camera can shoot at a shutter speed of at least 1 / 25 s. < / P > < p > [Key words]: special for C frame refers to the lens only applicable to APS-C frame camera. If it is installed on aps-h or full frame camera, there will be obvious black area around it. Continue ReadingDeveloped a “plug and play” solar power generation scheme, and “5B” won a $12 million round a financing