What is the ISO value? What's the point?

Sensitivity, also known as ISO value, is a measure of the sensitivity of negative film to light, which is determined by the measurement of sensitivity and several values, and has recently been standardized by the International Organization for Standardization.

For the negative with low sensitivity, it takes a long exposure time to achieve the same imaging effect as the negative with high sensitivity, so it is usually called slow negative. Highly sensitive negatives are therefore called fast negatives. Whether it is digital or negative photography, in order to reduce the exposure time, the relative use of higher sensitivity usually leads to the decline of image quality (due to thicker negative particles or higher image noise or other factors).

Extended data

The ISO sensitivity means that if you choose a higher ISO sensitivity under the same EV exposure value, you can get the same exposure with a faster shutter speed under the same aperture. On the contrary, a smaller aperture can be used to maintain correct exposure without changing the shutter.

Therefore, when shooting in dim light, you can often choose a higher ISO sensitivity. Of course, for SLR cameras, you can also choose to use a larger caliber lens to improve the luminous flux. For ordinary digital cameras, because they use a fixed lens, only by improving the ISO sensitivity can they adapt to shooting in dim light, especially when auxiliary light cannot be used.

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