What is a constant aperture? Many people haven’t heard of the three advantages working at critical moments

Have you ever met this kind of situation? When you go to buy a lens, you will find that the price of similar lenses of the same brand is quite different. There is always one lens that is different and expensive. Why is that? Why? < / P > < p > because it is a constant aperture zoom lens. What? Constant aperture? Yes. Since it is a zoom lens rather than a fixed focus lens, how to achieve a constant aperture? It’s not easy to do, but the principle is very simple. Next, poison master will take you to understand the principle and advantages of constant aperture lens. < / P > < p > constant aperture zoom lens refers to a lens whose maximum aperture remains unchanged no matter what focal length. That is to say, its maximum aperture is not affected by the change of focal length. No matter how much focal length you set the zoom lens to, you can use its nominal maximum aperture. In contrast, it is the non constant aperture zoom lens. Most of the zoom lenses we see are of non constant aperture. For example, Canon’s 18-135mm lens is marked with 1:3.5-5.6, in which 1:3.5-5.6 means that when the focal length of the lens changes from 18mm to 135mm, the maximum aperture can be reduced from f3.5 to f5.6. In other words, the maximum aperture decreases with the change of focal length. The lens with the maximum aperture floating is a typical non constant aperture zoom lens. < / P > < p > there may be some questions from my partner. How can the change of aperture be so small when the focal length changes from 18mm to 135mm? This is because during the zoom process, the actual aperture diameter of the lens is also changing, and some aperture will be lost at the long focus end of the zoom lens. < / P > < p > according to the formula, F value of aperture = lens focal length / effective aperture diameter of lens. If you want to keep the aperture unchanged, there are two solutions. One is that the three parameters in the formula are quantitative, which leads to the fixed focus lens; the other is that the three parameters in the formula are variables, that is, the constant aperture zoom lens explained today. < / P > < p > speaking of the three parameters in the formula are variables, the most difficult thing is that the effective aperture diameter of the lens is also a variable. When zooming, another diaphragm linkage is needed to control the luminous flux. At present, the constant aperture is mainly realized through the optical path design. For example, if the lens is marked with 70-200 mm f / 2.8, it means that the lens can shoot with the maximum aperture f2.8 in the 70-200 mm focal length. < / P > < p > the maximum F value of a constant aperture zoom lens is unique, so it is not surprising why the price of constant aperture zoom lens is so expensive. Although the price is expensive, the constant aperture zoom lens also has many advantages. Because the aperture is constant, the constant aperture zoom lens is very suitable for shooting in the case of dark or weak light, which can obtain relatively fast shutter speed and make the imaging more stable and clear. Moreover, the exposure can be controlled more efficiently because of the constant light input. The aperture will affect the depth of field, no matter what focal length, we can get as small depth of field as possible to get a more illusory background, especially suitable for shooting portrait. Friends no longer have to worry about changing the depth of field after changing the focal length. The constant large aperture lens has relatively good image quality and fast focusing speed, so it belongs to the professional lens. It is not recommended for beginners to buy constant aperture zoom lens at the beginning, because it will hinder people’s understanding and experience of aperture, shutter and ISO. < / P > < p > generally speaking, the constant aperture zoom lens has no other disadvantages except expensive. You can decide according to your budget and quality requirements. Photography is a step-by-step process, and you don’t need to buy all kinds of lenses or equipment at once. After all, only more practical operations can improve the shooting skills and perception. The lens or equipment is only auxiliary equipment. You should not seize the sesame and lose the watermelon. Huawei mate40 concept machine exposed, Kirin 1020 + curved surface full-scale screen, beauty hanging on iPhone 12