What is the relationship between exposure and sensitivity?

The relationship between exposure and sensitivity can be imagined as fetching tap water with a bucket. Water flowing down from the water pipe into the bucket is like light entering the camera, and exposure is equivalent to this process. When the water fills the bucket, it is overexposed, and the amount of exposure is equivalent to the amount of water in the bucket. This is generally determined by the shutter time and aperture size in the camera.

It can be imagined as the time the faucet is turned on and the size of the water flow. Sensitivity is the sensitivity of the film or photosensitive element in the camera to light. If the sensitivity is high, that is to say, the film or photosensitive element in the camera is sensitive to the entry of light, then the light can be recorded by the camera faster, which means the bucket can be filled with water faster.

Extended information:

Sensitivity, also known as ISO value, is a measure of the sensitivity of a film to light. It is determined by sensitivity measurement and measurement of several values. Recently, it has Standardized by the International Organization for Standardization. For less sensitive films, a longer exposure time is required to achieve the same image as a more sensitive film, so it is often called a slow film. Highly sensitive films are therefore called fast films.

Whether it is digital or negative photography, in order to reduce the exposure time, using a higher sensitivity will usually lead to a reduction in image quality (due to coarser film grain or higher image noise or other factors) . Digital cameras achieve the purpose of increasing ISO by increasing the light sensitivity of the photosensitive device or merging several adjacent photosensitive points.

Reference: Sensitivity_Baidu Encyclopedia