If you take a closer look at the camera, it consists of three main elements, each of which is responsible for its own exposure parameter:
the lens (always in the first place) is responsible for setting the aperture. The aperture determines the amount of light that enters the sensor by reducing the area of the hole through which it passes by exactly half in one step (the square root of 2 is 1.414141). Modern cameras allow even half a step, be careful – the standard aperture values are: 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, extremely rarely further. This is the denominator of a fraction, for example, 1/1, 1/1.4, 1/2, etc. Closing the aperture (increasing the aperture value, the denominator), you increase the depth of field, opening it reduces it.
The camera is responsible for setting the shutter speed. Shutter speed is the time interval during which light, passing through a lens limited by the aperture, is projected onto the plane of the photosensitive element (matrix, film). In modern conditions, shutter speed is also electronically controlled, and therefore can also be changed in half a step, but the standard shutter speed change step is also two-fold – in seconds 30, 15, 8, 4, 2, 1, 1/2, 1/4, 1/8 , 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, etc. By increasing the shutter speed, you blur the movement (including hand shaking and the flow of water), by reducing it, you can freeze it.
the matrix or film (actually located in the camera, but we consider it separately) is responsible for the sensitivity. Sensitivity is the susceptibility of the photosensitive element to a stream of light limited by the aperture and the exposure time frame when projected onto the area of the photosensitive element. The standard units of the International Standards Organization (ISO) are used to measure sensitivity around the world, from which it got its name. The sensitivity of the matrix can be changed before each frame, also twice in one step. The same goes for film, the sensitivity of which can be easily changed from cassette to cassette. Digital cameras today can change the sensitivity in a third of a step, but the standard values are within the range of ISO 25, 50, 100, 200, 400, 800, 1600, 3200, 6400, 12800, 25600, etc. By increasing the sensitivity, you increase the film grain and noise of the matrix, reducing, reducing.
It would seem that there is so much freedom for a photographer… But there isn’t, there is no freedom in life, there is no freedom in photography either – just like within a frame, being squeezed by three exposure parameters, the photographer has to live in a rather rigid coordinate system with three dimensions.
By the way, let’s make a reservation right away: it is usually assumed that there are two exposure parameters, aperture and shutter speed, however, this was true until recently, when the photographer, getting used to the film, believed that this parameter was unchanged. Today, it changes as quickly as shutter speed with aperture, although a separate wheel has not been invented for it even in DSLRs.