Why is the aperture smaller when the focal length is longer?

Aperture f value = lens focal length/lens aperture diameter, so the longer the focal length of the zoom head, the smaller the aperture.

What is an aperture?

Aperture is a device used to control the amount of light entering the photosensitive surface of the fuselage through the lens, usually in the lens. We use the f value to represent the aperture size.

Aperture f value = lens focal length/lens aperture diameter

As can be seen from the above formula, to achieve the same aperture f value, the aperture of a long focal length lens is larger than that of a short focal length lens. The complete series of aperture values is as follows:

f 1，f 1 .4，f2，f2 .8，f4，f5 .6，f8，f 1 1，f 16，f22，f32，f44，f64

It is worth mentioning here that the smaller the f value of the aperture, the more light enters in the same unit time, and the light entering amount of the upper level is exactly twice that of the lower level. For example, if the aperture is adjusted from f8 to f5.6, the amount of light entering will double. We also said that the aperture should be opened one level. For consumer digital cameras, the aperture f value is often between f2.8-f 16. In addition, many digital cameras can adjust the aperture by 1/3.

Aperture and shutter take precedence.

In addition to providing automatic mode, advanced digital cameras usually have two options: aperture priority and shutter priority, so that you can decide a certain aperture value or a certain shutter value on some occasions, and then match the appropriate shutter or aperture respectively to present different depth of field (sharpness) or effects.

Aperture priority exposure mode

After we decide the aperture f value ourselves, the camera metering system will automatically choose the appropriate shutter speed (which can be an accurate stepless shutter speed) according to the light conditions at that time. A digital camera with an exposure mode dial usually engraves the letter "A" on the dial to indicate the aperture priority mode (see Figure 4). Aperture prerequisite mode is suitable for photography that emphasizes the depth of field effect.

Because the focal length of digital camera is much shorter than that of traditional camera and the aperture of lens is small, it is difficult to produce narrow depth of field. Some digital cameras have a special portrait exposure mode, using built-in programs to blur the foreground and background.

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