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Films classified by speed
- Jun 20, 2018 -

According to the speed of speed iso100, iso200, iso400 and so on. If the value is doubled, the exposure required for exposure will also double, and the larger the value, the faster the speed. Of course, many other speed representation methods have been used before. The common ones are the American ASA system and the German DIN system ("fixed" system). China adopts GB (that is, the national standard) system, which is equivalent to DIN system. According to GB system, it can be divided into fast film (above GB24°), medium speed film (GB21°), and slow film (GB18°). For each additional GB3°, the sensitivity is doubled. For example, the GB24° film is twice as fast as the GB21° film. Various sensitivity standards can be converted to each other. ASA100 is equivalent to GB21° or 21DIN.

Films are based on speed (ISO), from the lowest speed of ISO25 degrees to high speed ISO3200. In general, the lower the sensitivity, the finer the picture quality. There are commonly used type 120 size (large film), type 135 (the most commonly used, film width 35mm), type 110 (small size), etc., as well as other for shooting ads or large posters such as 4 "*5" or 8"*10" large negative film. Divided by the photosensitive type, there are black and white film, color film, infrared film and so on. The color negative film adjusts the color tone of the photograph according to different light sources, and is divided into a daylight film and a light film. If a light film is used to shoot the scene in the daylight, the color of the photograph will be blue.

The commonly used negative film specification is 135. Under the constant popularization of digital photography, there are not many film stills that are used for filming, and the film still has its irreplaceable advantages, for example, the area of 135 film is much better than most digital camera light plates (digital media). Large, if you want to make large photographs, it is still better to use negative film. In addition, the film image has a strong sense of layering, natural color (color produced by analogy), fine picture quality (high pixel), and large tolerance (easy to keep highlights or shadows. For details, etc., the image quality is better than the digital camera. Especially when the light is dark, it may require long-time exposure shooting, or sensitization development (increasing the developer concentration or lengthening the development time) when rinsing the film, such as Kodak Tri-X400 sensitization developing to iso1600, or even Kodak T-maxp3200 The sensitization developed to the iso6400 also has good image quality, but long exposures produce a lot of noise in digital photography, so some photographers still insist on using film to shoot.

Although shooting with a film can produce high-quality photos, this requires familiarity with darkroom techniques. Generally speaking, it is difficult for fast print shops to take full advantage of their negatives. Therefore, it is best for photographers with negatives to print photos, for example, when printing photos. Implementing zoning exposure, self-adjusting photo contrast and cutting, and also because the toxicity of the medicine used in black-and-white printing is far lower than that of color printing, and the printing process is relatively simple, so many people do manual printing in black and white darkrooms, and most color negatives use automatic printing machines. Avoid contact with color printing potions, but manual printing is better than automated printing machines.