Camera aperture knowledge

 The lens of an industrial camera has a device that controls the amount of light transmission, called the aperture. The larger the aperture, the greater the amount of light transmitted; the smaller the aperture, the less the amount of light transmitted. But the aperture alone cannot fully describe the intensity of the light acting on the film. The distance between the lens and the film is also related, that is, it is related to the focal length of the lens. The smaller the aperture is, the closer the film is, the stronger the effect of light. There is a noun-the aperture factor. The aperture factor is the value obtained by dividing the focal length of the lens by the diameter of the aperture, which is expressed by f.

   For example, if there is an A, B, and C lens, the focal length of the A lens is 50mm, and the maximum aperture diameter is 25mm, then the aperture factor is 50/25 = 2, and we say it is a f2 lens; the focal length of the B lens is 35mm, and the maximum aperture diameter is 17.5 mm, the aperture factor is 35 / 17.5 = 2, we also say that it is a f2 lens; the focal length of a C lens is 100mm, and the maximum aperture diameter is 25mm, then the aperture factor is 100/25 = 4, we say it is an f4 lens ． The aperture of lens B is smaller than that of lens A, but the aperture factor is the same, so the intensity of light transmission to the film is the same; the aperture of lens C is the same, but the aperture coefficient is different, so the intensity of light transmission to the film is different ． The apertures of all camera lenses have been standardized, namely f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, etc.

The aperture has two functions:

1. Control the amount of light penetration: the intensity of light passing through the lens to the film is inversely proportional to the square of the aperture coefficient, that is, the intensity of the light acting on the film by the two adjacent apertures has a relationship of twice. f2 is twice as large as f2.8, and f2.8 is twice as large as f4.

2. Adjusting the depth of field: The so-called depth of field is the clear range that can be imaged before and after the lens is in focus. Its lens focal length, aperture, and the distance of the subject of the subject are related. The shorter the focal length of the lens, the smaller the aperture, and the distance of the subject. The larger the depth of field, the larger the clear range, and vice versa. So as far as the aperture is concerned, the small aperture has a large depth of field, which clearly and distantly shows the sharpness of the far and near; the large aperture has a small depth of field, which can make the subject stand out and express the blurring sense of the subject before and after the subject. It is worth mentioning that if the front and back scenes are clear, a small aperture should be used, but it should be small enough to cover the desired depth of field. It does not have to be too small, too small will be affected by diffraction, but will reduce its resolution!