What is the relationship among aperture, shutter and sensitivity?

Aperture, shutter and sensitivity form an "exposure triangle". The relationship among them and their action principle on exposure are shown in the following figure, in which one step is increased and the other step is decreased, and the exposure amount remains unchanged. Therefore, the three can be adjusted and changed according to their own needs on the basis of determining the accurate exposure (such as automatic metering with a camera).

The shutter controls the exposure time. The higher the shutter value, the shorter the exposure time and the darker the picture, and vice versa. Aperture controls the size of the lens entrance aperture. The larger the aperture value, the smaller the actual aperture and the darker the picture, and vice versa. Sensitivity controls the sensitivity of the sensor to light. The greater the ISO value, the more sensitive the sensor is to light and the brighter the picture, and vice versa.

Extended information:

For example, if you want to take a portrait with blurred background in broad daylight, you need a large aperture in the blurred background, but a large aperture will increase the brightness, especially in sunny days, and the picture will be overexposed. At this time, you should consider increasing the shutter speed to reduce the brightness until the brightness is normal.

If you use a low-end camera (the highest shutter of the low-end camera is 1/4 second) and the sun is shining and it is still overexposed even in 1/4 second, you need to put a dimming filter or a medium gray filter in front of the camera.