Knowledge analysis of SLR camera lens. No regrets after reading it.

The lens is the most important part of a SLR camera, but the larger the aperture of the lens, the greater the practical value. The advantages of large aperture lens mainly include: it is convenient for hand-held camera to shoot with field lamp in dim light; It is convenient to capture the effect of small depth of field and combine the picture with reality; It is convenient to use a higher shutter speed to cure the moving body. However, the manufacturing process of large aperture lens is complicated, so the larger the aperture, the larger the lens and the higher the price. Let's take a look at the lens knowledge analysis of SLR cameras with Bian Xiao.

Lens focal length of SLR camera

From a practical point of view, the focal length of a lens can be understood as the distance from the center of the lens to the film plane. Theoretically, it is defined as the vertical distance from the optical center of the lens or lens group to the focal plane when the scene at infinity forms a clear image on the focal plane through the lens or lens group. For a fixed-focus lens, the position of its optical center is fixed; For zoom lens, the change of lens optical center brings about the change of lens focal length.

The focal length of modern 135 camera lens ranges from 6mm to 2000mm, and the common focal length range is 15mm to 600 mm For a camera with the same frame and facing the same subject, the change of imaging effect caused by the change of lens focal length can be summarized as follows:

1, the focal length of the lens is inversely proportional to the viewing angle. Long focal length and small viewing angle mean that you can shoot large scenes from a distance; Short focal length and large viewing angle mean that you can shoot a wide range of scenery at close range.

2. The focal length of the lens is inversely proportional to the depth of field. Long focal length and small depth of field mean that the clear range of foreground and background is small; Short focal length and large depth of field mean that the clear range of the scene before and after is large. Depth of field is an important theoretical and practical problem in photography.

SLR camera lens cleaning

1 first of all, let's start with the structure of SLR. Let's take a look at the structure of SLR. Because the lens needs to be replaced frequently, the eyepiece and front mirror are generally exposed, and the reflector, focusing screen and rear mirror are also exposed, which may have dust.

2. The top lens of the lens group in front of the lens mainly plays a protective role and has little effect on lens imaging. Some dust and even fingerprints accumulated on it will not affect the imaging. If it is too dirty, it will mainly affect the anti-glare ability of the lens, that is, reduce the imaging effect of the camera backlight, and this lens also has a very durable coating, which can be said to be very durable. If there is no hard damage, it is better to polish it with coins and sandpaper. Or the corrosive solution is spilled, which will not be damaged basically, especially the original coatings such as Canon and Nikon, which are much stronger than our common UV and glasses coatings. If you choose the right lens pen to wipe, you can safely clean it boldly and leave some wiping marks. This is no problem, and you don't have to worry about affecting imaging anymore.

3. The last lens of the rear lens group of the lens is also coated, but it is much more fragile than the protective lens on the front lens group. The most important thing is that this lens has a great influence on imaging, so be careful when handling it. This kind of lens is often recessed at the end of the lens, which is less likely to get dust, but it is more laborious to clean. If the netizen is not skilled, then the lens pen is the best choice to clean this part, whether it is water, dust or fingerprints.

4. Behind the rearview mirror group is a reflector. Many netizens think this part is quite fragile. In fact, the reflector is not as unbearable as imagined. The texture of the silver-plated reflector is relatively stable. When cleaning, we should pay attention to the large particles of dust on it, so that the reflector will be polished by dust and there will be unnecessary scratches when wiping. A cotton swab dipped in clean water, soft lens paper and lens pen can all be used as tools to clean the reflector. the key is

5. There is a frosted focusing screen on the reflector. At this time, you should pay attention. This part is the most delicate place we clean. Whether you are a cotton swab or lens paper, it is very easy to leave scratches, and these scratches will be reflected in the viewfinder, so you must be very careful when handling this part. If you have some hair, you can turn the camera upside down and blow it away gently with air. If you can't blow it off, don't blow a lot into it, so it's easy to blow the dust directly behind the focusing screen.

6. We suggest that users go to the maintenance point to clean the dust behind the focus screen. According to our experience, although most cleaning methods introduced online are feasible, there is a certain probability of failure in operation. Cleaning this part requires a clean environment, and it is best to build a clean room in the bathroom. Moreover, when the focus screen is turned on, dust will easily enter the pentaprism at the top of the SLR. Unless you are willing to disassemble it, it is really hopeless.