In sand table training, the main influencing factors of exposure

Three elements of exposure: aperture, shutter, ISO

(These three factors determine the exposure, or in other words, if any two parameters are known, the other one can be uniquely determined).

1. Aperture: often referred to as f1.4f2.8f4f5.6f8f11f16f22f32; each step represents one stop of exposure, that is to say, f2 is one stop smaller than f1.4. It can be seen that the aperture corresponding to one exposure level differs by 1.4 times. Why?

It is actually a ratio. Aperture = lens focal length/clear aperture. (So, the markings on old lenses are mostly 1:1.4) In other words, taking the lens head as an example, 50mmf2, the actual clear aperture at this time is 25mm.

After understanding this, you can understand why the exposure is one stop different and the aperture difference is 1.4 times. (Because since this ratio is related to the aperture, the amount of light passing through is obviously proportional to the cross-sectional area, and the area is proportional to the square of the diameter.)

Understanding this, you can also understand why the telephoto large aperture Lenses are so expensive. Taking a 200mmF2 lens as an example, its clear aperture at the maximum aperture is 100mm, so its front lens must not be less than 100mm; while a 50mmF1.4 lens has a clear aperture of only 50/1.4 at its maximum aperture. =35mm. Therefore, the telephoto and large-aperture lenses you see are usually relatively thick, and because the lenses are relatively large, they are naturally heavy. The resulting lens servo system must be precise and driven quickly, and is naturally expensive (of course , this is just one of the reasons why it is expensive)

You can also understand why there are floating aperture lenses, such as 18-35/f3.5-5.6. Why 3.5-5.6? (At the 18-end, the maximum aperture is set to f3.5, but as soon as you zoom, the aperture changes by itself?) Do you understand, this is a way to save costs. Because of a constant aperture zoom lens, such as a 70-200/f2.8 lens, at the 70 end, the aperture at the maximum aperture is 25mm, and at the 200 end, the aperture at the maximum aperture is 71mm. In order to obtain a constant f2.8 aperture, the front lens must be considered close to the telephoto end throughout the zoom range. Therefore, the main function of a constant aperture zoom lens

The main function of the aperture is: depth of field (controlling the range and degree of haziness, whether it is a block of color or just enough to understand the content; the clear range)

A side effect is that it affects shutter speed.

2. Shutter speed: expressed in time. 30s, 15s, 8s, 4s, 2s, 1s, 1/21/41/81/151/301/601/1251/2501/5001/10001/2000....

Similarly Adjacent shutter speeds differ by one exposure stop. Obviously, the numerical difference is doubled.

The main function of the shutter is: freezing (whether it is clear or ghosting, the most important concept is the safety shutter---see how to take clear photos for details)

The side effects are: impact The size of the aperture.

3. ISO sensitivity: The national standard indicates ISO100200400800160032006400....

Similarly adjacent ISOs differ by one stop of exposure. Obviously, the numerical value is a series of 2.

The main function of ISO is to use faster/slower shutter speeds or smaller/larger apertures

The side effect is noise. The higher the ISO, the more obvious the noise will be, and the worse the image quality will be; but increasing the ISO allows you to use a smaller aperture or increase the shutter speed, which is beneficial to the realization of the photographer's intention.