What do you mean by SLR, wide angle and focusing in digital cameras?

Single lens reflex (SLR) is the most popular framing system at present.

In this system, the unique design of the mirror and prism enables the photographer to directly observe the image passing through the lens from the viewfinder. It can be seen from the structural diagram of a single-lens reflex camera that the light passes through the lens and reaches the reflector, and then refracts to the focusing screen above to form an image. Through the eyepiece and pentaprism, we can see the scenery outside in the observation window. When shooting, press the shutter button, the reflector will pop up, and the shutter curtain in front of the film will be opened at the same time. The light (image) passing through the lens will be projected on the film to make the film sensitive, and then the reflector will immediately return to its original state, and the image can be seen in the viewfinder. This structure of the single-lens reflex camera ensures that it is shot through the lens, so that the image seen in the observation window is always consistent with the image on the film, and its framing range is basically consistent with the actual shooting range, eliminating the parallax phenomenon of the paraxial head-up framing camera. From the perspective of learning photography, it is very conducive to intuitive framing and composition.

Wide angle: photographic terminology

Refers to the wide-angle lens to be shot.

Wide-angle lens is a kind of lens, which has a wider angle of view and shorter focal length than the general lens, and is suitable for shooting large-area objects.

Generally, the focal length of a wide-angle lens is 38-24 mm and the viewing angle is 60-84 degrees. The ultra wide-angle lens has a focal length of 20- 13 mm and a viewing angle of 94- 1 18 degrees.

Because the wide-angle lens has a short focal length and a large viewing angle, it can shoot a large area of scenery in a short shooting distance. Therefore, it is widely used to shoot large-scale landscape photography. In photography creation, shooting with a wide-angle lens can achieve the following effects:

First, it can increase the sense of spatial depth of photographic images.

Second, the depth of field is long, which can ensure that the scene before and after the subject can be clearly reproduced on the screen. Therefore, the vast majority of modern pocket automatic cameras (commonly known as fool cameras) use ordinary wide-angle lenses of 38-35 mm

Third, the lens covers a large area and shoots a wide range of scenery. wide-angle lens

Before introducing the wide-angle camera, let's know the focal length of the camera. In fact, when people talk about the focal length of a digital camera, they are not talking about the actual focal length of the digital camera, but about the equivalent focal length, that is, the focal length relative to the traditional 135 camera. From the principle of photography, the smaller the focal length, the wider the field of vision, and the wider the range of scenery that the photo can accommodate; The larger the focal length, the narrower the field of view, which means that you can shoot distant objects.

Focus: The English name of focus is Focus. Generally, digital cameras have various focusing methods, namely, auto focus, manual focus and multiple focus.

Auto focus:

Traditional cameras use a similar visual ranging method to achieve autofocus. The camera emits an infrared ray (or other rays), determines the distance of the subject according to the reflection of the subject, and then adjusts the lens combination according to the measurement result to realize automatic focusing. This automatic focusing method-direct, fast, easy to realize and low cost-sometimes makes mistakes (when there is something else between the camera and the subject, such as glass, or the light is insufficient, automatic focusing cannot be realized), and the accuracy is poor. Today's high-end cameras generally don't use this method. Because the camera actively emits rays, it is called active, and because it is actually only ranging, it is also called non-TTL because it does not judge whether coking is correct through the actual imaging of the lens.

Compared with active autofocus, passive autofocus was developed later, that is, judging whether coking is correct according to the actual imaging of the lens. The basis of judgment is generally contrast detection, and the specific principle is quite complicated. Because this method is realized by lens imaging, it is called TTL autofocus. It is precisely because this autofocus method is based on lens imaging, which has high focusing accuracy and low error rate, but the technology is complex, the speed is slow (except for the advanced autofocus lens using ultrasonic motor) and the cost is high.

Manual focusing:

Manual focusing, that is, manually turning the focusing ring to adjust the camera lens, so as to make the captured photos clear, largely depends on the judgment of the human eye on the image on the focusing screen, the photographer's proficiency and even the photographer's vision. Early SLR cameras and paraxial cameras basically used manual focusing to complete the focusing operation. Now quasi-professional and professional digital cameras, as well as SLR digital cameras, are equipped with manual focusing function to meet different shooting needs.

Multi-focus:

Many digital cameras have multi-focus function or area focus function. When the focus center is not set in the center of the picture, multi-point focus or multiple focus can be used. In addition to setting the focus position, you can also set the focus range, allowing users to take photos with different effects. Common multi-point focusing includes 5: 00, 7: 00 and 9: 00.

Holographic autofocus

Holographic AF is a unique function of Sony digital camera and a brand-new autofocus optical system. It uses advanced laser holography technology to detect the edge of the object by laser spot. Even in the dark environment, it can take photos with precise focus, and the effective shooting distance is 4.5 meters.