Ask experts to introduce some photographic terms, such as reversal film, aperture, depth of field, multiple exposure, speed and so on.

Color film can be divided into two types, namely reverse film and negative film. Color reversal film, sometimes called slide (positive film), is a kind of film that can directly get transparent positive color after reversal development. The color reversal film can be viewed by projecting the image directly onto the screen through the slide projector or on the observation light box. It can not only print and play photos directly, but also be used as the original film for color separation and plate making. The color reversal film is truly saturated, and the clarity and sharpness of the image are relatively high. However, compared with color negative film, the exposure latitude is relatively narrow, a little insufficient or excessive, which will affect the imaging quality. Therefore, the exposure must be very accurate when making a reverse film. Color negatives are mainly used to print and play color photos. After shooting and developing, color negative with orange cover can be obtained, whose light and shade are opposite to the subject, and their colors are complementary. The advantage of color negative film is that exposure latitude is big. Generally, the exposure is less than one level or more than two levels, and satisfactory images can still be obtained. In addition, color negatives are quite universal to the change of color temperature, and the color balance and contrast can be adjusted again through the color filter of magnifying glass when printing and playing photos. The English brand suffix of COLOR negative film is color, and the suffix of reverse film is krom. On the film box marked in English, negative film and negative film can be distinguished according to the above two suffixes. In addition, according to the color temperature balance, color films can also be divided into two categories: daylight type and illumination type. Sunlight color film is suitable for shooting under the illumination of sunlight or electronic flash with a color temperature of about 5500K, and light color film is suitable for shooting under light sources such as iodine tungsten lamp with a color temperature of about 3200K K.. If you shoot with daylight film under the light with a color temperature of about 3200 K, the picture will appear orange-red, and a blue color temperature conversion filter should be added in front of the camera. On the contrary, if you shoot with a light film in the sun with a color temperature of about 5500K, the picture will be blue, and an amber color temperature conversion filter should be added in front of the lens to get accurate color reproduction.

Negative is used to take pictures. Requires high sensitivity and tolerance.

Feature films are for showing. It requires fine particles, large contrast, small fog, high resolution and high definition.

Aperture is a device used to control the amount of light entering the photosensitive surface of the fuselage through the lens, usually in the lens. We use the f value to represent the aperture size.

Aperture f value = lens focal length/lens aperture diameter

As can be seen from the above formula, to achieve the same aperture f value, the aperture of a long focal length lens is larger than that of a short focal length lens.

. The complete series of aperture values is as follows:

f 1，f 1 .4，f2，f2 .8，f4，f5 .6，f8，f 1 1，f 16，f22，f32，f44，f64

It is worth mentioning here that the smaller the f value of the aperture, the more light enters in the same unit time, and the light entering amount of the upper level is exactly twice that of the lower level. For example, if the aperture is adjusted from f8 to f5.6, the amount of light entering will double. We also said that the aperture should be opened one level. For consumer digital cameras, the aperture f value is often between f2.8-f 16. In addition, many digital cameras can adjust the aperture by 1/3.

Aperture and shutter take precedence.

In addition to providing automatic mode, advanced digital cameras usually have two options: aperture priority and shutter priority, so that you can decide a certain aperture value or a certain shutter value on some occasions, and then match the appropriate shutter or aperture respectively to present different depth of field (sharpness) or effects.

Aperture priority exposure mode

After we decide the aperture f value ourselves, the camera metering system will automatically choose the appropriate shutter speed (which can be an accurate stepless shutter speed) according to the light conditions at that time. A digital camera with an exposure mode dial usually engraves the letter "A" on the dial to indicate the aperture priority mode (see Figure 4). Aperture prerequisite mode is suitable for photography that emphasizes the depth of field effect.

Because the focal length of digital camera is much shorter than that of traditional camera and the aperture of lens is small, it is difficult to produce narrow depth of field. Some digital cameras have a special portrait exposure mode, using built-in programs to blur the foreground and background.

Depth of field: In short, when we focus, the scene on the negative shows a completely clear distance range, and

It is "a clear range before and after the focus."

There are many reasons why multiple exposure technology is unique in photography. It is important that photography is an art, and every photographer will be happy to create a masterpiece with novel ideas and characteristics. However, the ability of a single photo to express a moment is limited after all. This limitation from time and space urges photographers to find a way to transcend and break through-to create artistic effects in different time and space on a single photo by using multiple exposures.

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