What does 123 mean?

Photography 123 means: focal length: the lens of a camera is a group of lenses. When parallel rays pass through a lens, they converge to a point, which is called the focal point, and the distance from the focal point to the center of the lens is called the focal length. A lens with a fixed focal length, that is, a fixed focus lens; The lens whose focal length can be adjusted and changed is a zoom lens. In the field of photography, the focal length mainly reflects the lens angle. For the traditional 135 camera, the viewing angle is about 50mm close to the human eye, and the lens that does not deform when shooting is called a standard lens, generally covering the range of 40-70mm, 18-40mm is called a wide-angle or short-focus lens, 70- 135mm is called a medium-focus lens, and135-. The CCD of a digital camera is generally much smaller than that of 135 film, so the focal length of the lens is much shorter at the same viewing angle. For example, a digital camera with a CCD of 0.33 \ \ \ \ ",when using a lens of about 13mm, its viewing angle is roughly equivalent to the standard lens of a 50mm 135 camera. Because the specifications and models of CCD used by digital camera manufacturers are different, everyone uses the term equivalent to the focal length of 35mm camera (that is, 135 camera). Depth of field: when shooting, the process of adjusting the camera lens to make the scene clear at a certain distance from the camera is called focusing. The point where the scene is called the focus. Because "clarity" is not an absolute concept, the scene imaging before and after focusing (near the camera) can be clear. The sum of the front and back ranges is called the depth of field, which refers to the scene within this range. The depth of field is first related to the focal length of the lens. The lens with long focal length has small depth of field, while the lens with short focal length has large depth of field. Secondly, the depth of field is related to the aperture. The smaller the aperture (the larger the numerical value, for example, the aperture of f 16 is smaller than f 1 1), the greater the depth of field. The larger the aperture (the smaller the value, for example, the aperture of f2.8 is larger than that of f5.6), the smaller the depth of field. Secondly, the depth of field in the foreground is smaller than that in the back, that is to say, after precise focusing, the scene in front of the focus can be clearly imaged, while the scene in the back of the focus is clear. Hyperfocal distance: Because the back depth of field of the lens is relatively large, people call the distance that can be clearly imaged after focusing as hyperfocal distance. Fool cameras generally use hyperfocal distance, which makes use of the feature that the scene can be clearly imaged at a certain distance with a short-focus lens, omitting the focusing function. Therefore, generally, low-grade fool cameras can't focus automatically, so they can only use hyperfocal distance. As mentioned earlier, "clarity" is not an absolute concept, and the scenery in hyperfocal distance is not really clearly imaged. Because there is no focus, it must be blurred, but the degree of blur is generally acceptable. This is the reason why the negative film taken by a fool's camera can't be enlarged too much. AF (Auto Focus) Auto Focus: There are several ways of auto focus, which can be divided into active and passive according to the control principle. Active autofocus is to use the camera to emit a beam of light (usually infrared), determine the distance of the object according to the reflected light signal, and then automatically adjust the lens to realize autofocus. This is the earliest autofocus method, which is simple to realize, fast in response and low in cost. It is mostly used for mid-range fool cameras. The accuracy of this method is limited, and it is easy to lose focus. For example, when there are reflective objects such as glass in front of the subject, the camera can't distinguish them correctly. Passive focusing is a bit bionic, that is, it is accurate to analyze whether the object is in focus, but it is difficult to focus accurately in low illumination because of its complex technology and high cost, and it is mostly used in high-end professional cameras. Some highly intelligent cameras can also lock moving objects and even control the focus with their eyes. AE (Automatic Exposure): Automatic exposure means that the camera automatically determines the exposure according to the light conditions. From the basic principle of photometry, it can be divided into incident type and reflection type. The incident type determines the exposure combination by measuring the brightness of the light shining on the camera. This is a simple and rude control, mostly used for low-end cameras. The method of reflection is to measure the fading, grazing and soil refining, kindness, beauty and bag health of rst persimmon caries books. From the perspective of metering methods, it can be divided into spot metering automatic exposure, center focusing automatic exposure, multi-point balance automatic exposure and so on. , each with its own advantages and disadvantages, is suitable for different lighting conditions or shooting purposes. From the control process, it can be divided into aperture priority, shutter priority, mixed priority, program control and predetermined mode. As the name implies, aperture priority is to determine the aperture used first, and the camera determines the appropriate shutter speed according to the calculated exposure. This method is suitable for situations where a predetermined depth of field is needed or the light ratio is adjusted with a flash. Speed priority is to determine the shutter speed first and let the camera choose the appropriate aperture size to shoot moving objects; Mixed priority is to make up for the deficiency of single priority by first determining the range of aperture or shutter, and then determining the exposure combination by the camera; Program control is to expose the camera according to the pre-programmed control program; The preset mode refers to that manufacturers preset reasonable exposure parameters for shooting according to several common lighting conditions, generally including: night scene, scenery, portrait, sports, etc. Aperture is one of the most important photographic elements in photographic creation. In addition to controlling the input of light to meet the needs of exposure, it is also an important means to obtain specific artistic effects. Unity of opposites between large aperture and imaging quality. Generally speaking, the imaging quality is relatively poor at large aperture, but the imaging quality of the new generation lens has been greatly improved at the maximum aperture. By making full use of the imaging characteristics of large aperture, unique images can be obtained. Because the depth of field is small at this time, it is convenient to clearly reflect a specific area and highlight the main body when other parts are relatively blurred. When the light is poor, such as shooting with a hand-held camera, you can use a high-speed shutter with a large aperture to prevent the vibration of the machine from affecting the imaging clarity. Some photographers rarely use the maximum aperture, and usually only use f5.6 and f4. In order to give full play to the characteristics of the maximum aperture, they should dare to use the maximum aperture. For example, the aperture of a large aperture standard lens can completely use the maximum aperture such as f 1.8, f 1.4, while the aperture of a medium telephoto lens should dare to use the maximum aperture f2.8 at this time, combined with the camera distance and the distance between the background and the subject (the farther the background and the subject are, the picture quality of the maximum aperture may not be as good as that of the medium aperture, but the loss in this respect is still worthwhile compared with the artistic effect obtained. When blurring the background, you usually choose a large aperture or a telephoto lens. How big is the aperture? In fact, except for telephoto lenses with a focal length of 200mm or even longer, the maximum aperture is generally used. When shooting with a standard lens, you may choose the maximum aperture f2.8 or even f 1.4. Only in this way can you get a unique charm and really separate the subject from the background. Because the depth of field of digital cameras is relatively large, it is difficult to highlight the subject without using the maximum aperture. 3. Small aperture and long depth of field. Small aperture is often used to obtain large depth of field when shooting scenery films, but factors such as lens focal length and shooting distance must be combined. If you use a telephoto lens, even if you use f32 aperture, you won't have much depth of field at a distance of 2-3 meters. In other words, as long as the subject and background are at infinity, there will be a great depth of field even if the aperture is large. 4. The aperture size varies with the subject. In figure photography, large aperture is often used, while landscape photography has more opportunities to use small aperture. To shoot a stream, it takes 1/8- 1/2 seconds to show the movement of the running water. Not using a small aperture will inevitably lead to overexposure; If you shoot the shadow of a wave ship under the backlight, if you use small apertures such as f22 and f32, the tiny wave light on the water surface will have the effect of adding a starlight mirror; When shooting fireworks and other subjects, because it takes 1/2s- 1s exposure time to perfectly present the shape of fireworks, it is also necessary to choose a small aperture. 5. Use tripod for small aperture. Shooting still life scenery and other subjects with small aperture requires high imaging clarity. F22 aperture is used for medium illumination, and the shutter speed is often around 1/30 seconds. In the absence of a tripod, camera shooting by hand often affects the clarity because of machine vibration, human physiological movement and other factors. Therefore, in the case of low illumination, use a small aperture and make full use of various brackets to support the camera reasonably. If you use a digital camera, you can improve the sensitivity to make up for it.