How to use the aperture priority on SLR?

Lead: If you want to know how to use light first, you must first understand what aperture is and how it affects the imaging effect. Let's have a look. 、

What is the aperture?

Aperture refers to the amount of light entering the photosensitive element through the camera lens, which is controlled by adjusting the amount of light on the photosensitive surface in the lens. The aperture value is represented by f, and f is the ratio of lens focal length to lens aperture diameter. Simply put, it is to control the amount of light entering through the change of aperture size, so as to achieve different exposure effects. For example, if the aperture is adjusted from F8 to F5.6, the amount of light entering will be doubled and the aperture will be enlarged by one level.

Embodiment of aperture size change on lens

Because the aperture value (the ratio of the focal length of the lens to the aperture diameter of the lens) is reciprocal, there is such a corresponding relationship: the smaller the aperture value, the larger the aperture of the aperture and the greater the amount of light entering, so the shallower the depth of field, the more obvious the blurring effect of the background and the brighter the picture. On the contrary, the smaller the aperture, the smaller the light input, the deeper the depth of field, the clearer the background and theme, and the darker the picture.

Relationship between aperture and aperture value and depth of field

There are two real-life examples to help you understand: students who have owned cats will find that cats' pupils will shrink into a vertical line during the day, so reduce the amount of light to ensure that they can see more clearly; At night, the pupil will automatically Zhang Kaicheng a round hole to increase the amount of light. In addition, nearsighted people will squint if they want to see things clearly without glasses, which can be compared to narrowing the aperture, deepening the depth of field and making the field of vision clearer.

Next, two sets of real shots are used to show the relationship between aperture change and light input and depth of field:

With the decrease of aperture, the amount of light entering decreases gradually.

? ? ? ? ? ? ? ? With the decrease of aperture, the clearer the background, the weaker the blur effect.

Aperture priority mode

Knowing the shooting effect that aperture can bring, you can try to use aperture priority mode. The letters Av (Canon camera) or A (Nikon camera, Sony camera) are usually used to indicate' aperture priority exposure mode'. This mode is based on the aperture value. After manually determining the aperture size, adjust the shutter and sensitivity according to the environment, and finally give the appropriate exposure.

? Av logo on Canon, a sign of Nikon.

How to adjust the aperture? Just turn the thumbwheel on the SLR body, turning to the right means that the aperture value becomes larger (the aperture becomes smaller because it is inversely proportional), the exposure effect becomes darker and the depth of field becomes larger; Dialing to the left means that the aperture value becomes smaller (aperture becomes larger), the exposure effect becomes brighter, and the depth of field becomes shallower. Canon and Nikon have slightly different thumb wheel positions.

? Canon wheel is above the fuselage; Nikon's wheels are on the back of the fuselage.

It is worth noting that in the aperture priority mode, you can directly pull the dial wheel to adjust the aperture value, but in the range of m, pulling the dial wheel defaults to adjusting the shutter speed. At this time, you need to hold down the exposure compensation key and then pull the dial wheel to change the aperture value.

? Canon exposure compensation key is on the back of the fuselage; Nikon exposure compensation key is above the fuselage.

Xiao Bai may encounter such a problem when adjusting the aperture value. Obviously, the lens is marked with f/3.5 of the maximum aperture, why can't the wheel reach 3.5 when it turns to the end? We mentioned earlier that the aperture value is the ratio of the focal length to the aperture, so when using the zoom lens, the aperture value will change with the change of the focal length. For example, a general lens will be marked with 18-55mm f/3.5-5.6, which means that the maximum aperture is 3.5 when the focal length is 18mm, but the maximum aperture is reduced to 5.6 when the focal length is 55mm.

The lens will show that the maximum aperture changes with the focal length.

When adjusting the aperture value, it is not best to adjust it to the maximum or minimum. The best real imaging quality is the aperture value that stays in the middle. When the aperture diameter is too small, there will be serious light diffraction, while when the aperture is too large, there will be phenomena such as out-of-focus, distortion, color difference and purple edge. Generally speaking, the best aperture is at the position where the maximum aperture of the lens is reduced by 2 to 3 levels. If the maximum aperture of a lens is 1.4 and the minimum aperture is 16, the imaging performance of aperture 4 or 5.6 will be better.

Aperture priority application

After learning to use aperture priority mode, how to choose the appropriate aperture? It can be decided according to the content of shooting. Generally speaking, when shooting portraits, still life and other objects that need to highlight the main body, large aperture and shallow depth of field can achieve the effect of first solid and then virtual, which can make people pay more attention to the focus center and blur unnecessary interference and debris. The soft background or foreground created by a large aperture is more likely to present a fresh feeling of literature and art in addition to focusing on the line of sight.

Large aperture brings blurred foreground and background effects.

Use f/ 1.2 large aperture to shoot portraits, and the blurred background presents a literary atmosphere.

Use f/ 1.2 large aperture to shoot animals. The aperture is so big that the cat hair is blurred.

In addition, the large aperture can also be used for hand-held shooting in low light environment to avoid blurring the picture. For example, when shooting indoors, on cloudy days, at night and so on. , requires a longer exposure time (slower shutter speed). At this time, using a large aperture can increase the light input of the photosensitive component per unit time to a certain extent, thus improving the shutter speed and avoiding the blurring of the photo.

Medium aperture is usually used by documentary photographers when shooting documentary humanistic subjects. Because it is necessary to show the correlation and interaction between characters and their environment at the same time, large aperture cannot be used to blur the background excessively.

The middle aperture records the interaction between people and the environment (picture from the network)

The middle aperture records the interaction between people and the environment (picture from the network)

Small aperture and large depth of field can be used to photograph urban buildings and large scenes. Small and medium-sized apertures such as f/8, F/1,f/ 16 are often used with short-focus wide-angle lenses to show rich details and delicate levels.

Small aperture shooting magnificent natural scenery (picture from the network)

Small aperture shooting magnificent buildings (picture from the network)

Small aperture can also shoot a unique star-studded effect. If there are point light sources such as the sun and street lamps in the shot picture, choose F/1,f/ 16 or even f/22 small aperture to shoot, and these point light sources will present beautiful Starlight Glimmer effect. The number of stars depends on the number of diaphragm blades of the lens used. If the aperture blades are odd, the number of stars photographed is twice that of the aperture blades; If it is an even number, the number of stars photographed is consistent with the number of blades in the aperture.

The small aperture captures the Starlight Glimmer effect of the street lamp (picture from the network)

This is something about the aperture. Do you know more about aperture? Are you more confident in using aperture priority mode? Pick up your camera and experience the special charm of different apertures. If you have some confidence after learning the basic knowledge of shutter and aperture, you can also try to combine them and shoot with manual stop. Maybe you can get rid of it? Xiaobai? One step closer to the title.