What is a SLR camera?

We often hear people say "SLR camera". What is a SLR? Single lens reflex (SLR) is the most popular viewfinder system, which is used by most 35mm cameras. 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. Therefore, you can accurately see the same image that the film is about to "see". The core of the system is a movable mirror (as shown in the light blue part), which is placed in front of the film plane at an angle of 45. The light entering the lens (as shown by the red light path) is reflected upward by the mirror to a piece of ground glass. Early SLR cameras had to hold the camera waist-high and look down at the ground glass. Although the image on the ground glass is upright, it is upside down. In order to correct this defect, the current eye-level SLR cameras are equipped with a pentaprism above the frosted glass. This prism reflects light many times to change the light path and send the image to the eyepiece. At this time, the ground image is upright up and down, and corrected left and right. When framing, most of the light entering the camera is reflected upward by the reflector to the pentaprism. Shutters of SLR cameras are almost always directly in front of the film (because they are located in the film plane, they are called focal plane shutters). When framing, the shutter is closed and no light reaches the film. Press the shutter button, the reflector quickly turns up to get out of the way, at the same time, the shutter opens, the light reaches the film, and the shooting is completed. Then, the mirrors in most cameras will be reset immediately.

This necessary tilting of the mirror also brings some other problems:

First, the viewfinder will be blocked at the moment of taking pictures. Because the shielding time is only a moment, this is not a big problem for the image that is reset immediately. However, it also raises some emergency issues. For example, when using stroboscopic shooting, you will not be able to see whether the stroboscopic device flashes normally through the viewfinder.

Second, the noise of the mirror moving. This may become an important problem where silence is needed. Because there is no moving mirror that suddenly blocks the light path in the ranging camera, this noise will not be generated.

Third, the vibration of the camera, that is, the overall movement of the camera caused by the tilting action of the mirror. Suppose you shoot at a shutter speed of 1/500 seconds, don't worry. This vibration will not be detected. However, if you take accurate photos at a low shutter speed, such as with a telephoto lens in low light, this vibration may cause great problems in imaging.

In addition, there is another problem with SLR framing. For example, if we want to shoot with a small aperture like f/32, the light allowed into the lens by f/32 is very weak, which will cause the image seen in the viewfinder to be blurred, and it may be difficult to focus or even impossible to focus at all.

In fact, the solution of SLR is quite clever. It will first use the maximum aperture of the lens to complete the framing and focusing. When the shutter is pressed, the aperture of the lens will immediately shrink to the preset aperture to complete the film exposure. At the moment when the exposure is completed, the aperture will be opened to the maximum aperture to prepare for the next shooting.

First of all, there are several reasons for choosing digital SLR:

The professional positioning of digital SLR cameras determines that even popular products for ordinary users and enthusiasts have many advantages, which is also the fundamental reason why many enthusiasts choose digital SLR cameras. We can summarize the professional characteristics of digital SLR as follows:

1, advantages of image sensor

For digital cameras, the photosensitive element is one of the most important core components, and its size is directly related to the shooting effect. In order to achieve good shooting effect, the most effective method is not only to increase the number of pixels, but also to increase the size of CCD or CMOS. Whether using CCD or CMOS, the sensor size of digital SLR cameras is much larger than that of ordinary digital cameras. Therefore, the number of sensor pixels of digital SLR is relatively large (currently the lowest is 6 million), and the area of a single pixel is four or five times that of a civil digital camera, so it has excellent signal-to-noise ratio and can record a wide brightness range. The image quality of a 6-megapixel digital SLR camera definitely exceeds that of an 8-megapixel 2/3-inch CCD camera.

2. Rich lens selection

Digital camera is a product of optical, mechanical and electrical integration, and the performance of optical imaging system is also very important to the final imaging effect. Having an excellent lens is as important for imaging as the choice of image sensor. At the same time, with the cost reduction of image sensor, image engine and storage equipment, the proportion of optical lens in the cost of digital camera is also increasing. This is especially true for digital SLR. In the choice of traditional SLR cameras, the richness and imaging quality of lens groups are important factors in the choice of film friends. In the digital age, the retention rate of lens group naturally becomes the basis of brand competition. Canon, Nikon and other brands have huge autofocus lens groups, from super wide angle to super telephoto, from macro to soft focus, users can choose matching lenses according to their own needs. At the same time, due to the large sensor area, it is easier for digital SLR cameras to obtain excellent imaging. More importantly, many photographers generally have one or two or even a dozen professional lenses, all of which are purchased by photographers with their hard-earned money. If they buy a digital SLR camera body, the lens will be revitalized at once, and they will form two complementary film and digital systems with the original traditional film camera.

3. Fast response speed

The biggest problem of ordinary digital cameras is that the shutter lags behind for a long time. If you don't master it well, you will often miss the most wonderful moment. Response speed is the advantage of digital SLR. Because their focusing system is independent of imaging equipment, they can basically achieve the same response speed as traditional SLR, which makes users handy in news and sports photography. At present, Canon's EOS1D Mark Ⅱ and Nikon D2H can reach the continuous shooting speed of 8 frames per second, which is comparable to traditional film cameras.

4. Excellent manual control ability

Although the camera's automatic shooting function is getting stronger and stronger today, a user who has certain requirements for photography will not be satisfied with shooting only in automatic mode because of the ever-changing environment and shooting objects. This requires that digital cameras also have the ability of manual adjustment, so that users can adjust according to different situations to achieve the best shooting effect. Therefore, the function of manual adjustment has become an essential function of digital SLR and a professional representative. Exposure and white balance are two important aspects in many manual functions. When the automatic metering system cannot accurately judge the light and color temperature of the shooting environment, users need to judge according to their own experience and make mandatory adjustments manually to achieve good shooting results. This is also the embodiment of the professionalism of digital SLR. For example, EOS 10D can adjust the color temperature value on the basis of 100K every time to help users get the best effect.

5, rich accessories

An important difference between digital SLR and ordinary digital camera is its strong expansibility. In addition to continuing to use additional lenses such as polarizers and interchangeable lenses, you can also use auxiliary equipment such as professional flashlights to enhance your ability to adapt to various environments. For example, high-power flash, ring macro flash, battery handle, timing remote controller, these rich accessories make digital SLR adapt to various unique needs, while ordinary digital cameras are greatly inferior.