When the sensitivity of photographic film is fixed, in order to obtain the correct exposure film, the combination of lens light transmission area and exposure time should also be fixed. camera lens

This is a problem of equal exposure. The three elements of exposure are: sensitivity, aperture and shutter, each of which will affect exposure. When an ideal exposure is achieved, if you change one of them, but you don't want to change the exposure, you must change one of the other two to balance it.

Just as it has been assumed in the article that the sensitivity is constant, when the aperture is enlarged (from f/ 1 1 to f/5.6), the light transmission capacity will double and then double, and the natural photos will be brighter than the original exposure. But now to maintain the original exposure, we can only reduce the exposure time by speeding up the shutter and darken the photo to the original exposure. Well, as long as you can understand the above, the problem is coming.

In the aperture values in the above table, the number of bits is reduced by one step, and the exposure is halved. The number of bits is reduced by one step, and the exposure is doubled.

The shutter is also understood in this way. The exposure time of 1/500 seconds is only half that of 1/250 seconds, while the exposure time of1125 seconds is twice as long.

The conclusion is that the aperture is from f/ 1 1 to f/8 and then to f/5.6, and the equivalent exposure shutter is from115 seconds to 1/30 seconds and then to 1/60 seconds.