What does the quality of the lens determine? The more specific the better! Please forget to say one or two things, because I know more than one or two things, thank you.

The first thing to pay attention to when choosing a lens is the focal length of the lens. The focal length is actually a matter of viewing angle, and different focal lengths have different viewing angles. In addition, users should be clear about themselves, what is the main purpose of my purchase of lenses? Whether to shoot scenery or people, and so on. As we all know, it is advisable to use a wide-angle lens to shoot landscapes and a telescope lens to shoot people. Therefore, we must first decide the lens focal length we want to buy according to the purpose of photography.

The best focal length for shooting scenery is 24mm wide-angle focal length and 200mm telescopic focal length (both are subject to 35mm specifications, the same below). When the wide-angle focal length of the standard zoom lens evolves from 28mm to 24mm, the viewing angle becomes larger and the range of scenery that can be accommodated is greatly broadened. Generally speaking, the maximum aperture of the lens is not too high for shooting scenery. If you mainly shoot scenery, when choosing a zoom lens, it is basically enough to choose a wide-angle focal length of 24 mm. As for the focal length of the telescope, it should be at least 200 mm. If the focal length of the telescope is 300mm or 400mm, it will be more ideal, and the degree of freedom will be greatly improved. The telephoto focal length of the traditional zoom lens is 300mm, while it is 450mm when used in digital SLR, and the focal length is enlarged by 1.5 times, which makes people feel happier when used. This is the value of digital SLR. At present, the wide-angle focal length of digital special ultra-wide-angle lens is generally 12mm, which is equivalent to 18mm of 35mm specification, which is nearly 1.5 times larger than the focal length of 28mm of 35mm specification, thus greatly expanding the left and right range of shooting landscape scenes.

The best focal length for shooting people is 85 mm. According to the standard of 35mm, the lens is selected based on the focal length of 85 mm.. The portrait taken with a focal length of 85mm is basically close to the picture taken by a medium format camera, which not only has a suitable sense of distance, but also the face of the person looks natural, and the distance between the camera and the person being photographed can basically be kept at the usual speaking distance. 85mm focal length can also blur prominent people in the background. In order to obtain a good blur effect, it is appropriate to choose a lens with a larger maximum aperture. The focal length of 85mm is about 135mm on a digital SLR. Although the distance of the lens is a little weak, it is basically no problem, so the focal length of the lens should be at least about 85 mm

A macro lens of 100mm is enough for traditional SLR. 100mm macro lens can shoot flowers at the same time, but when shooting at the same time or near the same time, it is easy to shake because of the long focal length and depth of field of the scene, so anti-shake measures should be considered when shooting. From this point of view, it is easier to use a 50mm macro lens on a digital SLR.

Second, the maximum aperture

The real value of the maximum aperture is to increase the amount of light entering in weak light, so as to achieve the best exposure combination. Shooting scenery generally does not require the blur ability of the lens, and in addition, except for particularly dark places, the requirements for lens caliber are generally not too high. However, when the 70-200mm zoom lens is matched with the 2x zoom lens to make the telephoto lens reach 400mm and focus automatically, it is best to choose the lens with the maximum aperture of F2.8, which is conducive to accurate focusing in dark conditions. Shooting people with a large aperture lens can shoot natural light with a mobile phone even in weak light. In addition, the lens with the largest aperture can bring faster shutter speed, so sports photography also needs a large aperture lens.

Another reason for requiring a large lens aperture is to freely blur the background to ensure the blur quality. When the aperture of the lens with the maximum aperture of F 1.4 is reduced to F2, both the imaging quality and the background blur quality are better than those of the lens with the maximum aperture of F2. Therefore, it is very valuable to reduce the aperture by one step with a large aperture lens, and any photographer should be good at using this feature of the lens.

Third, close-up ability

The close-up ability of the lens is another key point after the focal length and the maximum aperture. The same is true for wide-angle lenses, standard lenses and telescope heads. So, how big is the close-up ability?

First of all, the close-up ability of a wide-angle lens has almost nothing to do with the wide-angle lens, but when shooting a flower scene with a vast landscape as the background, it is often necessary to shoot the flowers a little bigger. In similar circumstances, the close-up ability of a wide-angle lens is very important.

The close-up capability of the existing 50mm standard lens is about 45cm, which basically meets the use. However, when the shortest shooting distance is used, the large-aperture standard lens often produces large aberration because of the lens protrusion, resulting in low imaging quality. We should be prepared for this when buying and using.

If you use a telescope to shoot scenery, there is not much requirement for close-up ability. But if it is used to shoot people or flowers, the close-up ability of the lens is very important.

Fourth, expressive force.

When many people choose a lens, the first concern is the clarity of the lens. The purpose of the photo determines what kind of sharp lens is needed. High-priced high-quality lenses are mainly used by professional photographers. If it's just general photography, there's no need to spend a lot of money on expensive and high-quality lenses. In addition, the imaging clarity of the lens is directly related to the aperture size. When a lens is reduced by one or two steps from the maximum aperture, the imaging clarity will be greatly improved.

Distortion is an optical phenomenon caused by the optical properties of lenses. It's impossible that every shot has no distortion. Manufacturers have corrected the distortion when producing lenses, trying to control the distortion to the lowest level. Generally speaking, there are three kinds of lens distortion: barrel distortion at the wide-angle end of zoom lens, pincushion distortion at the telephoto end and hat distortion after barrel distortion correction at the wide-angle end. As far as the current lens situation is concerned, the most prominent problem is the barrel distortion at the wide-angle end. Try to choose a style with small barrel distortion when purchasing.

Blur in photography is beyond the ability of human eyes, so it has aroused great interest. Fuzzy itself has quality problems, and there is a difference between cleanliness and filth. The background is blurred and beautiful, and the image appears soft; If it is blurred and dirty, the light will scatter to the four corners of the picture, and the blurred part is not in a beautiful circle. In severe cases, it will form a double blurred state. In an ideal lens, the light will be evenly dispersed, forming a very natural fuzzy state.

The ability of the lens to blur the background is also related to the lens aperture. Many lenses become sharp immediately after shrinking from the maximum aperture by one or two steps, but their blur ability is relatively reduced. The image taken by the ideal lens with the largest aperture is also very sharp and the blur effect is also very good.

In backlight photography, halos and light spots will be formed on the screen due to the repeated reflection of strong sunlight or other strong light sources on the mirror. This small part of the light that forms halo and flare will not only be imaged on the screen, but also form random reflection in the mirror, which will reduce the imaging quality. In order to prevent this phenomenon, backlight photography must use a hood. Excellent lens adopts the process of completely preventing halo and glare in the manufacturing process, and the contrast is good even if it is shot in reverse light.