With the aspheric lens and floating lens structure, the optical quality of the wide-angle lens is further improved. Today, we can buy wide-angle lenses with various focal lengths on the market, whether it is fixed focus or zoom. And the image quality is unimaginable decades ago. However, the shorter the focal length of the lens, the more problems it will bring, such as distortion, glare and vignetting.

　　1) Distortion

　　 The distortion of the picture taken by the wide-angle lens is inevitable. Wide-angle will distort perspective, making closer subjects look larger, and farther ones smaller. This kind of distortion is a characteristic of wide-angle lenses, and if used well, it will create a dynamic picture effect. The vertical line is shot with a wide-angle lens to form a convergent perspective effect. For example, the sides of a building will slope inward. This is a matter of perspective, not a lens.

　　 If there is such an exaggerated effect, you need to adjust the angle of the camera up or down. Although distortion can make the subject look disproportionate, it sometimes creates an eye-catching or extraordinary effect. So when we need to do this, there is no need to correct this distortion.

　　 If we want to minimize the distortion effect, we should always keep the camera's focal plane and the subject in a parallel lens design state, or use a shift lens to shoot. In addition, it is also feasible to be at a longer distance and then change to a longer focal length lens.

　　 If none of the above methods are available, we can still deal with it through post-editing. Geometric distortion (or corner distortion) is also a common problem when using a wide-angle lens. Objects in the corners of the screen appear to be stretched.

　　 This phenomenon occurs when three-dimensional things are represented on a plane. The object in the center of the picture is basically real, while the objects on the periphery of the picture are elongated in an elliptical shape. The effect of objects in the corners of the screen is the most obvious.

　　2) Vignette

　　 The brightness drop at the edge of the image is called vignetting, which is usually not intentional or undesirable some. Because the wide-angle lens covers a large field of view, it is more prone to vignetting than other types of lenses.

　　 If you install a hood, filter holder or screw-in filter in front of the lens, vignetting is more likely to occur. The hood sometimes blocks the light in the four corners of the picture. The way to solve the vignetting is to remove these accessories, or use an ultra-thin filter designed for wide-angle lenses. Even without the occlusion of these accessories, vignetting may still occur with optical lenses, especially when using ultra-wide-angle lenses.

　　The appearance of the optical vignetting is because the rear lens is blocked by the lens in front of it. Because it reduces the effective lens aperture of the off-axis incident light, the result is a reduction in the light density at the edge of the viewfinder frame, which is more obvious when the aperture is widened. This phenomenon can be eliminated by reducing the aperture by 2-3 stops.

　　Many digital SLR cameras do not have 100% coverage of the viewfinder field of view, so it is possible that you may not notice the existence of vignetting when composing the picture. You can play back the picture and zoom in on the four corners to see if the light is dimmed. Vignetting can also be corrected by post-processing.

　　SLR lens selection tips

　　1) The lens is not a small investment, of course you don’t want to make a Regretful decision. Basically, which lens to buy depends on your budget and needs. If you like shooting wild animals, your first choice should be a telephoto lens or telephoto zoom lens.