Common sense about photography.

(a), light and exposure

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 higher the ISO value, the higher the sensitivity of the film/photosensitive sensor and the easier the exposure.

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.

Every time the aperture value jumps up and down, the exposure will be doubled or halved accordingly.

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 will double or half.

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

1. lens focal length

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.

2. Hole

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

3. Distance from the lens to the subject

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.

prospect

If there are too many blank parts in the photo or the color of the sky (ocean) in the background is not ideal, you can narrow the background or add foreground to it.

1. Generally speaking, the foreground is always clear, especially when shooting buildings. At this time, a relatively small aperture and wide-angle lens can be used.

At present, it is very popular for us to show some macro effects such as flowers, leaves and insects. When shooting these natural objects, the background is often blurred. In fact, you can also try to blur the foreground and express it with a large aperture and a telephoto lens, which will produce unexpected results. It's a pity that I can't map it yet. )

2. The choice of prospects is often different, and everyone's aesthetics are different. But generally speaking, the choice of prospect should not be too big, too beautiful and too bright, otherwise it will inevitably give people the feeling of unclear theme or usurping the role of host. But if the prospect is too dark, sometimes it will not be enough to set off the main body. Let's solve this problem by ourselves.

Don't stick to the rules.

In fact, this is just a very basic theory. Don't get stuck in the stereotype of composition, and don't stick to these principles, otherwise all photos will look the same.

There are many tips for composition, but not all of them are mentioned in my textbook. That's for everyone to experience. If there is an opportunity, I would like to communicate with you. But one thing, for beginners, before breaking these rules, it is recommended to practice well under these rules. If you make breakthroughs and innovations after practice, you will be more likely to succeed.

(5) lens

The lens is one of the most important parts of the camera, and it can also be said to be the core part of the camera. I only discuss the lens of 35mm camera here. The lens of a camera consists of several groups of optical lenses. Include concave lenses and convex lenses. A good lens needs high resolution (the ability to show details) and good contrast (the ability to show bright levels).

To some extent, the size of the subject on the screen can be controlled by the lens. When the camera is fixed at one point, the range of the scene we observe depends on the focal length of the lens. When a large landscape is photographed with a 15mm ultra-wide-angle lens, the 600mm telescope can only see an eagle in the tree at this time. There are many kinds of lenses we can usually buy, from fisheye lenses, wide-angle lenses, telescope lenses, macro lenses, zoom lenses and so on. However, for most ordinary digital camera users, it is impossible to prepare a bunch of lenses because the lenses are not replaceable and the price is too expensive. Let's take learning as the basis.

The main difference between vision and vision is actually the difference in perspective (that is, the range that the picture can contain). For example, the viewing angle of 15mm super wide-angle lens is 1 10 degrees, while the viewing angle of 600mm telescope lens is only 4 degrees. In addition, the viewing angles of 28mm, 50mm, 105mm and 200mm lenses are 75 degrees, 46 degrees, 23 degrees and 12 degrees respectively.

standard lens

In a 35mm camera, the lens from 50mm to 55mm is the standard lens, and its viewing angle is about 45 degrees, which is similar to that of human eyes. Therefore, the effect obtained by using this lens will be natural and comfortable.

wide-angle lens

A lens with a focal length of less than 50mm can be a wide-angle lens. A lens less than 20mm (including 20mm) can be a super wide-angle lens. A short focal length lens can get a wider picture, and a wide-angle lens will be very useful when you want to get a wider range of scenery. Wide-angle lens has the following characteristics:

1. Wide viewing angle can obtain a wider range of scenery than the standard lens. The viewing angle of 28mm lens is 75 degrees, which is equivalent to the viewing angle of human eyes. The lens viewing angle of 15mm can be increased to 1 10 degrees.

2. When shooting a long depth of field with a wide-angle lens, the foreground and background can be clear.

3. Lines will be distorted. When looking up or down with a wide-angle lens, the lines in the photo will converge from near to far. When the lens shoots a building up, it will produce the feeling that the building falls backwards.

4. The exaggerated perspective effect will be discussed in the following perspective.

5. The edge of the picture will be elongated due to the characteristics of spherical glass.

Telescope head

A lens with a focal length greater than 60mm can be called a telescope head, and the largest is said to be 2000mm, hehe, I have never seen it. It has the following characteristics.

1. Narrow viewing angle can only see a small part of the image, which can exclude some unwanted things and highlight the main body.

2. Shallow depth of field is opposite to wide-angle lens. The depth of field of the telescope head is relatively short. If matched with a large aperture, the background blur will be very strong.

3. The perspective effect of compression is also discussed later.

4. Enlarge the image When you can't get in, you can further enlarge the subject with a telescope.

zoom lens

Nowadays, many digital cameras are zoom lenses, and the popular ones range from 3 times to 12 times (not counting digital zoom). Zoom lenses are convenient and quick to use, but they often have disadvantages. Ordinary zoom lenses often have poor image quality and are not suitable for some very professional people. My flesh and blood are indistinguishable.

There are also some special lenses, including reflective lens, magnifying glass, fisheye lens and perspective control lens, which are not commonly used, so I won't say much. We'll discuss it later if you like. But there are also macro lenses, because it is very popular to show photos of macro function on digital cameras now. Digital macro function is often realized by zoom lens, but a real macro lens can only be regarded as a macro lens if it can focus at a very close distance and form a subject with at least 1/2 (0.5 times magnification), or more strictly speaking, it needs an image as large as the subject (1 times magnification).

Perspective effect

Finally, talk about the perspective effect. Telescopes can make people feel that the scene is getting closer and closer, and the distance between distant objects seems to be very close. Ultra-wide-angle lenses are the opposite. However, in fact, the perspective effect mainly depends on the distance between the camera and the subject. The lens is in the same position. When the lens is 600mm and the lens is 50mm, the same perspective effect will be found if the middle part of the photo is enlarged.

The perspective of wide-angle lens and telescope head was also mentioned earlier. Wide-angle lens can produce exaggerated perspective effect, making the objects in the picture farther away. Objects close to the lens become larger than normal and become the most prominent place on the screen, while distant objects are pushed back and become smaller than those seen by the naked eye. On the contrary, the telescope head can produce a compression effect, which makes the object feel closer than what the naked eye sees and produces a dense effect.

(6) light

Light is not only an important topic in photography, but also a difficult point. I have always found this part difficult to say, and this part has different opinions. If you have any questions, welcome to discuss. Light has many parameters: texture, direction, light source, color and so on. This paper mainly discusses how to control the corrected light and enhanced light in the process of photography. Some physical knowledge of light. Read the physics book yourself.

Texture of light

Outdoor, the texture of light is mainly influenced by the sun, clouds and atmospheric conditions.

1. Hard dimming

When the light mainly comes from small light sources (flash, five-block light bulb, direct sunlight, etc.). ), generally hard dimming. Hard dimming is often characterized by strong effect and large contrast. The subject usually has a clear shadow, and the details of most light and dark blocks in the photo may disappear because of too strong light.

2. Soft dimming

The light emitted by a large and diffuse light source (sunrise in the morning, cloudy weather) is called soft dimming. It is characterized by no clear directionality and weak contrast, even if there are shadows. It will not give people a strong visual impact, but it can show all the details in the photo well, which is suitable for documentary photos and people photos.

3. Fog

Fog is suspended particles in the air, just like adding a filter in front of the camera, which will reduce the contrast and soft colors. Make the whole look softer. But it will also reduce the clarity.