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Detailed explanation of basic knowledge of photography

Thin film/photosensitive sensor

The main parameters of film refer to the sensitivity of film, which is expressed by ISO value (abbreviation of International Organization for Standards). The greater the ISO value, the higher the sensitivity of the film sensor and the easier it is to expose.

hole

There is a set of overlapping metal blades in the camera lens. The aperture size and opening time of the blade determine the exposure of the primary phase, and also produce the aperture and speed of the camera.

When the exposure time is fixed, the larger the aperture, the greater the exposure of the film. Expressed in f/ value. The aperture values of general cameras are f/ 1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/1,f/ 16 and f/22.

shutter

Of course, it mainly refers to the shutter speed. As mentioned above, it is determined by the opening time of the metal blade. At present, the shutter speed of many cameras is controlled by the computer chip that comes with the camera. For traditional cameras or some semi-professional cameras, the shutter speed of the camera still needs to be manual, mainly including the following, from slow to fast, 1, 1/2, 1/4, 1/8,115. Similarly, every time the shutter speed jumps up or down, the exposure is doubled or halved.

Relationship between aperture and shutter

The larger the aperture, the shorter the relative exposure time (except in special cases). There are many different shutter speeds and aperture combinations that can get the same exposure value, but the exposure effect is not necessarily the same, because it also involves the depth of field, which will be discussed later. The lens with the largest aperture is called "fast lens" because it can match the faster shutter speed.

(2) Camera operation mode

At present, some low-end models of digital cameras, the so-called family models, are mostly fools with automatic focusing and exposure. There are two basic exposure modes for mid-range and above cameras: manual mode and semi-automatic mode. This is basically the same as a traditional camera.

Manual control

Not all cameras can. When the manual mode is selected, the combination parameters suggested by the exposure meter can be ignored. You can choose the aperture and shutter value completely automatically. How to make an ideal exposure depends on the specific situation and personal preferences at that time, and of course you need to practice more yourself.

Semi-automatic mode

Many cameras offer at least a semi-automatic exposure mode. Generally, one of the aperture and shutter speed is fixed first, and the other can be adjusted. Then there is what we often call aperture priority mode or shutter priority mode. The difference between them is whether to choose aperture or shutter speed first.

Situational mode or special topic mode

In fact, this model is very popular now. Many mid-range so-called semi-professional cameras have a knob, such as Canon G3, G5, olympu730 and above. We can use landscape, sports, people and other modes without manual steps. Among them, the landscape mode generally considers the depth of field, the sports mode focuses on higher shutter speed, and the portrait mode focuses on the appropriate large aperture. The exposure combination decided by computer chips is often much more ideal than that decided by some beginners.

(3) Depth of field

Sometimes you can see that the subject and background of some photos are very clear, and you have seen photos with only the subject clear and the surrounding out of focus. To produce these effects, it is necessary to involve depth of field.

When choosing a faster exposure speed, we usually need to use a larger aperture, so the depth of field will be shorter, the clear range of the photo will be smaller, and some scenes may be blurred; And if you slow down the shutter speed, then the aperture can be narrowed, and at this time, you may also make the unwanted part of the picture appear. Therefore, how to control the depth of field is a preliminary and important technology in photography.

concept

Simply put, the depth of field is the clear range of the photo scene. Theoretically, only the objects in the focal plane are clear, but due to the resolution of the naked eye, some objects before and after the focal plane are generally clear.

Related factors of depth of field

The focal length of the lens

The focal length of the lens is different, and the depth of field will be different. A long lens can produce a shorter depth of field effect, and a short lens can produce a longer depth of field effect.

hole

Generally speaking, the larger the aperture, the shorter the depth of field, the smaller the aperture and the longer the depth of field.

Distance between lens and object

The closer to the subject, the shorter the depth of field. or vice versa, Dallas to the auditorium

Depth of field range

Generally speaking, if a lens is not very special, the range of depth of field can include 1/3 in front of the focal plane and 2/3 in the back.

(4) Composition

Modern high technology can make focusing, photometry and exposure completely controlled by the camera's computer chip, but only the composition still needs to be done by ourselves, and the computer is not smart enough to choose its own scenery.

Tripartite principle

For hundreds of years, the traditional composition principle has been the criterion of art. This principle advocates that the subject should not be placed in the center of the picture. Under this principle, we can divide a photo into three equal parts, and then put the subject of photography at one of the intersections. For example, when you want to take a close-up, you can put the most wanted parts (human eyes, flower stamens, etc. ) At a certain intersection. If it is a large-scale landscape photo, you can put the horizon or sea level above 1/3 or below 1/3, depending on what theme you want to express.

Attention! Relationship between aperture shutter and image definition

One of the most interesting features of photography is that it is a combination of many factors, and one factor always affects the other. For example, in terms of image definition, the choice of exposure combination can affect the definition. When it comes to image clarity, many photographers first think of focusing. However, in addition to focusing, there are a series of factors that lead to unclear photos, such as the movement of the subject, camera vibration, lens pollution, insufficient depth of field, overexposure, light penetration, overdevelopment, moisture on the film or lens, and so on.

Here we will discuss three factors that affect the photographic clarity when choosing the exposure combination, namely, the depth of field, the motion of the subject and the camera vibration. When deciding the exposure combination for a specific subject, these three factors sometimes contradict each other, satisfying one factor, but bringing problems to the other, so you need to think twice about which exposure combination best suits your performance intention. The following three factors are analyzed respectively.

Shen Jing

Theoretically, when the lens focuses on a certain point, only the object at that point can form a clear image on the film. But in fact, the scenes in a certain range before and after focusing are also clear on the film. This range is called "depth of field". Please note that it is meaningful to use the modifier "clearer" here to describe clarity. Let's take an example to illustrate that if you take a close-up of a person's head with 135 film, the focus is on the eyes. If it is a contact mark, it is likely that the nose, mouth and ears of the subject are clear in this 135 photo. If it is a small enlargement, the nose tip and ears of the subject are not as clear as you think. When you zoom in to 12 X 15 with this 135 negative, you will find that only a small part of the subject's eyes are really clear. However, if you put this big photo of 12 X 15 on a shelf and look back ten feet, you will find that the clear part of the image in the photo has increased again. Step back a little, and you will feel that the images in the photo are very clear. This is why we must use the modifier "clearer" to describe the clarity produced by depth of field. The meaning of "clearer" depends largely on the size of the photo and the viewing distance.

In order to truly understand the meaning of depth of field in theory, we must first understand a concept, that is, fuzzy circle.

Whether a picture looks clear or not depends on the eye's ability to distinguish the details in the picture. If you can tell the difference, you will feel clear; I don't know if I can't tell.

When the lens focuses on a certain light spot (the image is composed of countless light spots), the image produced on the film is actually not a point, but a circle. No matter how small the circle is. The diameter can be measured. The largest circle as a point in vision is called a "fuzzy circle". It can be seen that for photos enlarged to the same size, the blur circle of the smaller negative should be smaller than that of the larger negative. The depth of field scale on the camera is also determined according to the fuzzy circle.

If you take a big picture or enlarge a small part of the negative at high magnification, you will find that the predetermined blur circle is too large. In this way, even the scene within the camera's depth of field scale will make people feel unclear. In the same way, the blur circle of a small negative is smaller than that of a large negative if it is enlarged to the same size, so as to achieve a clear effect. Because the actual magnification of small negatives is large. Therefore, in this case, if you want to get a clearer image, you can't rigidly apply the Jing Shenbiao on the camera. On the contrary, we should set more practical standards ourselves. The simplest method is to use a larger aperture depth scale. In other words, if F/8 is actually used for shooting, the depth of field is determined according to the deepest depth of F/5.6.

In addition to the above factors, the depth of field of a photo depends on three aspects: the focal length of the lens, the size of the aperture and the distance from the camera to the subject.

Lens focal length: the shorter the lens focal length, the greater the depth of field; The longer the focal length of the lens, the smaller the depth of field.

Aperture size: The smaller the aperture. The greater the depth of field; The larger the aperture, the smaller the depth of field. For a specific lens, when focusing at a certain distance, the depth of field is directly related to the aperture size. However, there is an optimal aperture for any lens. Although an aperture smaller than the optimal aperture can produce a greater depth of field, in terms of artistic effect; It will reduce the clarity of the image, not improve it.

Distance from the camera to the subject: Generally speaking, the farther the camera is from the subject, the greater the depth of field. Conversely, the smaller the depth of field.

Considering these factors comprehensively, it can be clearly seen that if you want to get the maximum depth of field as much as possible, you should use a short focal length lens, a small aperture and a long distance. If you want to reduce the depth of field as much as possible, then you should use a telephoto lens, a large aperture and a close range. These technologies should be used appropriately according to the actual needs of the picture.

Subject's movement

Not all subjects are static, but a large number of subjects are in motion. There are two ways to shoot a moving object: either shoot the action with a fast enough shutter speed to produce a very clear image, or use a slow shutter speed to produce a certain degree of blur. The degree of blur depends on the shutter speed used. According to the specific situation of the photo, the blurred image can indicate the speed of movement, some fantasy or low shooting technology.

Usually when shooting a moving body, you can decide in advance how to shoot this action. Is the high-speed shooting clear? Or follow the shooting at a slow speed? Is it to make the image extremely blurred? Or make the main part of the image clear and the secondary part blurred? Let's see how to achieve these effects.

Clear movement. As long as the shutter speed is fast enough, you can shoot any moving object clearly (of course, the photographer's response is also quite fast). However, the fastest speed of most inter-mirror shutters is limited to 1/500 seconds; Most focal plane shutters can only reach11000 seconds at the earliest. When a moving object with a speed of 30 miles is within 25 feet, even if it flies in front of the camera for11000 seconds, the image will still be blurred. Therefore, if you want to take a clear picture of the moving body, you must pay attention to three points: First, the speed of the moving body should not be too fast; Second, if your body is moving fast, don't do lateral movement in front of the camera. Third, if the moving body is fast, shoot as far as possible with the fastest shutter speed. Of these three cases, the third one is probably the least useful, because the image on the film may be too small. Second, maybe it can not only produce clear images, but also show motion. First, to achieve good results, there will probably be no problem.

The image is blurred. From the point of view of picture appreciation, moving pictures with blurred images are more reminiscent of movement, which is much more interesting or attractive than moving pictures with clear images. How blurred should the dynamic image be? This question mainly depends on everyone's hobbies. However, when you want to show the details of the moving body in the photo, the degree of blur should be as small as possible. Of course, this often depends on the actual motion of each part of the image. For example, if you shoot a car walking sideways, it may be that the whole car is slightly blurred; When shooting a person walking in the same direction, his feet may be very blurred, but his body is very clear.

When a moving body is moving back and forth (such as a walker's arm) or moving up and down (such as pole vault), there is a way to express dynamics or dynamics with slow speed. When this moving body reaches the limit in one direction and starts to move in the opposite direction, there is a stationary point. If you press the shutter at this static point, you can use a slower shutter speed to grasp the dynamics. For dynamic performance, this method is sometimes quite powerful.

Another way to shoot moving objects is to follow the shooting method. Subsequent shooting allows you to "capture" fast-moving objects at a slower shutter speed. This method is usually quite effective when it is used to move the lens horizontally, especially when the motion mode is single. For example, a motorcyclist can be recorded quite clearly at a very slow speed, even if the speed reaches 120 mph, because the motion pattern of the subject is single. On the contrary, for a runner, his feet are moving up and down and his arms are moving back and forth. The effect of shooting with the running method will be that the body parts are quite clear and the limbs are very blurred, because the runner's movement mode is not purely single.

These are several techniques for shooting moving objects. No matter which one is used, when choosing the shutter speed, it must be considered together with the aperture to achieve correct exposure.

Camera vibration

The slower the shutter speed, the greater the possibility that the camera will shake unintentionally. Most people can hold the camera steady when using the shutter speed of 1/60 seconds. Shutter speed slower than1/60s is easy to cause vibration. If you want to find out the slowest speed of holding a camera, you can do this experiment. Find a subject with a clear outline or rich details, make sure that the subject is still when shooting, and then shoot with a hand-held camera at a series of shutter speeds, such as from 1/8 seconds to 1/250 seconds. After development, check the effect of shooting at various speeds on the film. Use a magnifying glass or film projection on the screen to check (don't check the printed photos), from which you can check the ability to hold the camera steady. For example, if you find that the exposure time is slower than sub-seconds, it means that the camera is shaking, which tells you that you can't hold the camera with your hands below 1/60 seconds. When the shutter speed is lower than1/60s, a tripod or some support should be used to stabilize the camera.

Photographic Notes: Understanding Specification Sheet-Aperture.

The meaning of aperture

Aperture and shutter are two tools to control the amount of light in photography! We introduced it in detail in the last chapter. In this chapter, we will understand the structure of aperture. Aperture refers to the size of the opening in the middle of the lens, which controls the brightness of light when film or CCD is exposed. In fact, the aperture adjusts the amount of light according to the pupil structure of the human eye. The end of the aperture consists of a circle of thin and overlapping metal blades, and the openings of the blades form a circle. Zooming in or down can control the amount of light entering.

Aperture unit

The size of the aperture is determined by its aperture value (f number). Generally all lenses have this aperture series. In the specification table of the camera, the manufacturer usually provides two aperture values (see the red box in the attached figure). These two data, one by one, represent the maximum aperture value of the camera lens. One set of data refers to the aperture at the "wide-angle end", such as F2.6, and the other set is at the telephoto end. For example, the digital camera in the left specification table is a 3x optical zoom, so at the 3x optical zoom end, the maximum aperture is not F2.6, but F4.7 This figure also shows the range of the maximum aperture change of this camera when zooming.

Whether it is a digital camera or a fool camera, today's aperture representation still follows the traditional practice. The standard aperture series are: f/ 1, f/ 1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/1,f//kloc. F/ 1 is the maximum aperture value. In the above series, the adjacent aperture series and the subsequent series are half of the light quantity of the previous series. For example, the aperture of the lens is set to f/4, and the amount of light it lets in is half of that set to f/2.8; Or just the aperture is set to a quarter of the f/2 light amount.

Aperture formula

The numerical representation of the aperture is mysterious, but the larger the number, the smaller the aperture. In fact, the size of the aperture can be expressed by a formula, which is expressed in bold and bold as follows:

Aperture value (f $ NUMBER) = lens focal length (mm)/aperture (mm).

Let's take a 50mm standard lens as an example. If its maximum aperture (that is, the aperture of the aperture blade, not the aperture of the lens) is 36mm, then the maximum aperture value of the lens is equal to f/ 1.4(50/36 = 1.4). Because the aperture size is limited, the maximum aperture value also has its limit. At present, the maximum aperture of the standard lens of 135 traditional cameras is f/ 1.0, and the digital cameras are f/ 1.8 of Olympus C-5050Z series, followed by f/2.0 of professional digital cameras. Generally, the aperture below f/5.6 is called large aperture; Above the aperture f8, it is called a small aperture. The smaller the aperture, the wider the depth of field and the clearer the picture; The larger the aperture, the shallower the depth of field and the more blurred the picture. We will discuss the depth of field separately below.

The value of aperture

The change of aperture size can not only change the transmittance, but also control the depth of field. Especially in portrait shooting, the requirement of depth of field is emphasized. Because the maximum diameter of the aperture is mainly affected by the lens size of the lens, if you want to enlarge the aperture, you must enlarger lens under the standard specifications, and enlarger lens will lead to more expensive costs and manufacturing expenses. In the world of traditional cameras, if the aperture is larger than the previous level, the price will often rise in proportion. Therefore, no secular lens can have all the apertures when it is manufactured. For general-purpose 35mm camera lenses, the aperture is mostly from f/ 1.4 to f/22. Only the aperture of the special lens of the large camera (4X5) is as small as f/64, but the maximum aperture is also limited to f/5.6.

Aperture and depth of field

In the sample photo below, opening the aperture of the camera can speed up the shutter speed, which is very useful in dim indoor light. The large aperture allows you to take stable photos without a tripod. Secondly, the smaller the aperture, the deeper the clear range of the scene, which is also one of the definitions of depth of field.

In the following example photo, when shooting with a large aperture, the photo results show a fairly shallow depth of field, only the girl in the middle is clear, while the scenery behind is blurred. If you shoot with a small aperture, the photos you take will have a different feeling. For example, the landscape architecture below is the result of shooting with a small aperture. Focusing the lens in the middle, you can see a deep depth of field, and the foreground and background are enough for everyone to see clearly.

Monocular camera body, through the "depth of field preview key" you can see the change of depth of field range. When the aperture is reduced, you can see that the scenery becomes clearer and clearer on the observation window of the camera. Some traditional camera lenses also have depth of field scales, which can be used to calculate the range of depth of field.

Binocular cameras, consumer digital cameras or fool cameras can't directly show the scene through the optical observation window with the largest aperture of the lens. Similarly, you can't use other apertures to turn down the aperture to check the depth of field. This is because this kind of camera, in order to save cost, does not connect the lens with the viewfinder, but uses a simple second viewfinder, so it looks as clear as the subject at any distance.

Traditional and digital aperture markers

On traditional lenses, the ring at the bottom shows the aperture set by the lens. The top ring shows the focal length of the lens. When the lens is set with different apertures, there is a matching number corresponding to the aperture series on the middle ring, so the coverage from the closest to the farthest depth of field is clear at a glance. This kind of practice, which is similar to an engineering ruler, has been used to this day. But the lens of digital camera is very small, and a lot of information is digitized. Few digital cameras can predict the depth of field, and most of them rely on rules of thumb or digital operation. The aperture value of digital camera also moved to the TFT LCD screen on the back of the camera, and the LCD information display screen of traditional camera was gradually replaced by this method.