Why are lenses round instead of square?

The circular mirror can unconditionally accept all ranges (outward viewing lens), the square mirror has a sense of oppression (viewing window), and the image can be evenly projected on the photosensitive film (the developed photos should still be rectangular in negative design). If you want to build a square lens, it is not impossible. You can create a long lens by covering the lens with a shelter (the effect of widescreen in movies can be imagined like this). The lens is not completely round, but rather a curved lens. 1. Because light is radioactive, the distance from the focus to the mirror will optimize the image. 2. The production is relatively simple. 3. The circular lens has the widest field of vision. There are also special lenses, which are not round, but they are not easy to make. Camera introduction ...! ! ! A lens is a structure that focuses light, so that the film can get a clear image. Early lenses were all composed of a convex lens. Because of the poor definition, chromatic aberration will occur, which is gradually improved into a compound lens, that is, the combination of multiple concave-convex lenses to correct various aberrations or chromatic aberration. By coating the lens, the amount of light entering is increased, glare is reduced, and the image quality is greatly improved. Generally speaking, the lens used for photography is a focusing lens. According to the optical principle, the light from far away will all focus on one point after passing through the lens with focusing function, which is the focus. The distance from the focal point to the center of the lens is called the focal length. In a camera, the center of the lens is usually at the aperture, and the focus is on the focal plane (soft surface). So the focal length of the camera is the distance from the aperture to the film when the lens is focused at infinity. The focal length is usually expressed in millimeters on the lens, such as a 28 mm lens ... and is based on the focal length of a standard lens.

Those whose focal length is smaller than the standard lens are called short focal length lenses (wide-angle lenses), and those with large standard lenses are called long focal length lenses (telescope heads). The so-called standard lens means that the focal length of the lens is equal to the diagonal of the film. Accordingly, the diagonal of the 35mm film used by the monocular reflex camera is 43mm, so for the 35mm monocular reflex camera, the lens with a focal length of 4 mm to 55 mm is called a standard lens. Below this number is a wide-angle lens; This number has a telescope head on it. It should be noted that if the film size increases, the number of centimeters of its standard lens will naturally increase. For example, for a camera with a medium-sized 6X6cm film, the diagonal of the film is 85mm, so its standard lens is 75mm to 90mm. So, if 50 mm is a standard lens,

Strictly speaking, this is incorrect. Because it is suitable for cameras using 35mm film. But for a medium-sized camera using 120 film,

Then 50mm is a wide-angle lens. Usually, unless otherwise specified, it is generally regarded as the lens of 35mm film. Drawing an angle is also called viewing angle and taking an angle. That is, the angle formed by the connecting line between the lens center and the diagonal of the film is called drawing angle or viewing angle. The stretching angle is inversely proportional to the lens focal length, that is, the longer the lens focal length, the smaller the stretching angle, and the shorter the lens focal length, the larger the stretching angle. Generally speaking, when distinguishing lenses, there is also a method to distinguish them by telephoto angle, that is, those whose telephoto angle is close to the visual angle of human eyes are called standard lenses, that is, those whose telephoto angle is 45 ~ 55 degrees are called standard lenses, while those whose telephoto angle is 65 ~180 degrees are wide-angle lenses (wide angle means wide telephoto angle) and 35 ~ 2 degrees are telescope heads. The drawing angle not only affects the range of the picture, but also affects the size of the picture. That is, when the shooting distance is constant, the size of the image is directly proportional to the focal length of the lens. Wide-angle lens has a large painting angle and a wide shooting range. On the contrary, the image on the film is small, the telescope head angle is small, and the shooting range is small. The image on the same area of film is naturally larger, that is, the shorter the focal length, the smaller the image; The longer the focal length, the larger the image. Perspective refers to the relationship between scenes, where the near things are big and the far things are small. In the case of the same distance, only the sense of distance changes in photos taken with different focal lengths, but the relationship between the size of the scene does not change. There is no change in the size relationship between the image taken by the long lens (135mm) and the image taken by the standard lens (50mm). It can be said that the image taken by the telescope is only a small part of the wide-angle lens. However, if the shooting distance is changed and the main body of the picture is kept equal in size, the perspective effect will change greatly. Wide-angle lens has the effect of exaggerating perspective confusion, while telescope has the effect of compressing perspective confusion. It should be noted that the exaggeration or compression of perspective confusion is mainly affected by distance. Therefore, when using a wide-angle lens with the same distance as the standard lens, the sense of distance cannot be exaggerated. Only by shooting at a shorter distance than the standard lens and closer to the subject can the effect be exaggerated.