Shutter aperture sensitivity formula _ On aperture and shutter

Everyone has this experience: when you look at things in strong sunlight, your eyes will naturally narrow (the pupils of your eyes are narrowing); In the dim light, I will try my best to open my eyes (my pupils are also dilated). It turns out that the pupil plays a role in regulating the light throughput.

If you compare a camera to an eye, the aperture is like its pupil. This pupil consists of many metal lobules. As long as we turn the adjusting ring that controls the aperture, the leaflets will open or close evenly, showing the light hole we need. As shown in the figure below:

The camera lens is engraved with aperture coefficients of 2, 4.5, 5.6, 8, 1 1, 18, 22, etc. These data are the reciprocal of the effective aperture (the denominator value is the same), so the larger the aperture coefficient, the less the luminous flux. Therefore, in general photography, a small aperture can be used when the sun is bright, and a large aperture is needed when the light is dark. An important function of aperture is to control exposure (another function is to control depth of field, which will be discussed in the next issue).

Life experience also tells us that it is not enough to open and close the pupil only under different light conditions. Sometimes you need to close your eyes, and sometimes you need to open your eyes for a long time. This shows that the length of light incident time is also an important way to control luminous flux. For example, to fill a bucket of water, the pore size is like the thickness of a water pipe. The thick tube can be filled in a short time, while the thin tube takes a long time. If we compare the aperture to the pupil, then the shutter is the eyelid that blinks on the lens. On the lens, we can see such a series: b, 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000. Door b means that it can be exposed for a long time (press open and raise your hand to close). Subsequent data is the reciprocal of the time taken, that is, a fraction of a second. The bigger the number, the shorter the time. Which level of shutter to choose should be considered in combination with the choice of aperture, which can be confirmed in our photography practice: choose f4 1/500 seconds, F81125 seconds, f 16 1/30 seconds, and the shutter combinations of these different apertures. F 16 1/30 seconds will make the environment clear and difficult for athletes to identify. Which combination to choose depends on the situation and demand. When you need to increase the shutter speed one step to "fix" the moving object, you must open the aperture one step to get the correct exposure. When you need to lower the aperture by one step in order to get a greater depth of field, you must lower the shutter speed by one step. Mastering the relationship between them is extremely important for learning photography.

It is just a metaphor to say that the shutter opens and closes in a blink of an eye. In fact, the photographic visual effect achieved by high-speed shutter and slow door really makes our eyes candidly admit defeat. Nowadays, people shoot flying bullets at the speed of11000 seconds, leaving behind images that our eyes can't see clearly. The application of the slow door will achieve another peculiar effect: shooting the machines running in the workshop, the slow door will let you get a dynamic photo, "colorful clouds"; Shooting waterfalls in a stream with a slow door will turn running water into veils and silk. Taking pictures of the night scene of a city or construction site with B-door exposure for a long time will leave strips of light on the headlights of Mercedes-Benz, just like molten steel rushing. The following "Night Song" is the night view of the bridge taken by Gate B, and the lighting leaves a rhythmic curve, just like a symphony of night and light. The clever use of shutters and slow doors will continuously broaden our horizons and enrich our expressive force. May you master the wonderful use of aperture and shutter skillfully, and capture and express the myriad customs of our life.