Films of the same type can be roughly divided into four main characteristics: color sensitivity, sensitivity (film speed), granularity, and contrast.
1. The performance of color sensitivity and shade
Different types of films respond to colors differently, especially color films. If the film is more sensitive to a certain color, shooting with it will make an exaggerated expression of that color, because the rays of that color will act on more photosensitive crystals.
Let me talk about the problem of black and white film sensitivity. Most of the black and white films sold on the market are full-color films, that is, the sensitivity to all visible light is about the same as the sensitivity of the human eye. For example, light red shows a light gray tone on the photo, while dark red will appear as another dark gray tone on the photo. As for other colors, such as blue, yellow, green and so on. Although we can't see the color on the black and white panchromatic film, but we can see their relative brightness and darkness.
There is a film used in the printing industry called color blind film, which is sensitive to other colors except red. In this way, when you use it to shoot a scene, the red object on your negative film will appear relatively pale, or even become white, because the color blind film is characterized by red color blindness. Therefore, when the light from the red object hits the film as if there is no light on the film, the result is that a lighter or transparent image formed on the negative film is printed on the photo to become a darker image. The yellow or orange is roughly the same, because it is composed of red and yellow.
But color-blind films are only used for special purposes, such as printing and plate-making, and are only available in film packs. In fact, filmmakers rarely have the opportunity to use color-blind films, and even never use them, so you can ignore it.
Color film has greater flexibility in the sense of optical rotation. Different brands and different series of color film have different reactions to different shades of light. Some will have more intense colors, and some will have more contrast to individual colors. The good performances vary. In addition, the color film also has some strong reactions to color, the photos will be more gorgeous, otherwise the colors will be more loyal to the original.
As for the color performance of the color film, it can be divided into daylight type and light type. The former corresponds to normal daylight or the environment of electronic flash lighting. If it is used for tungsten lighting, it will be seriously yellowish; It must be used for tungsten filament lights. If it is used for daylight or flash, it will be seriously blue.
As for daylight slides, there are also cool and warm tones. The latter has a slightly lower color temperature, which is more pleasing for portraits.
As for infrared film, it is a special film sensitive to infrared light. There are colored infrared films and black and white, which are particularly sensitive to the infrared of the spectrum. When shooting light that is invisible to the human eye, it can produce strange special effects for artistic photography except for scientific and military purposes.
2. Sensitivity
Different films may have different sensitivity to light, that is, some films will require more or less light than other films to achieve normal exposure. Films that require less light are called high-speed films, whereas films that require more light are called slow-speed films or medium-speed films. Film's sensitivity to light is called Film Speed ​​or sensitivity.
However, it must be emphasized that the so-called film speed has nothing to do with the speed usually referred to in motion. The film speed only involves the sensitivity to the response to light. However, because the high-speed film has a strong response to light, at the same aperture, you can use a higher shutter speed to shoot higher, to shoot higher-speed action, so some photographers misunderstand that high-speed film is some use Filming high-speed action film.
Film speed used to have different systems in different regions for some time. For example, the United States used the ASA standard and Eastern Europe used the DIN system. But today, the international standard ISO is used globally, but in fact ISO is no different from the previous ASA, such as In the past, when ASA100 was equivalent to DIN21, the earliest ISO unification was called ISO100 / 21, but now it has been simplified to ISO100. In other words, DIN has been eliminated, and ASA has changed its name to ISO.
The ISO sensitivity of each film is provided by the film manufacturer and indicated on the packaging. The higher the sensitivity, the faster the film—that is, the greater the sensitivity to light. The ISO grades are ISO50, 100, 200, 400, 800, 1600 and 3200. The sensitivity of ISO200 film to light is one level higher than that of ISO100 film, while ISO800 is two levels faster than ISO200, and so on.
For example, ISO800 film is faster than ISO100 three levels, which means that if you shoot a certain scene with ISO800 film, the exposure combination used is 1/1000 second and f / 8, then the same scene with ISO100 film needs to increase the third-level aperture , That is, 1/1000 second, with f / 2.8 to get the same amount of exposure, calculated with the same example, if you shoot with ISO400 film, what aperture will you use at a shutter speed of 1/500 second? Yes, it is still f / 8.
So what does the ISO sensitivity marked on the film box mean to you? It actually tells you how much exposure the factory recommends when you want to get a "correct exposure" photo on the film. You can adjust the ISO speed indicated on the film box on the camera. The camera's metering system will use this film as the exposure calculation; however, due to the different characteristics of the film, the photographer also has some exposure Preferences, so some photographers will make adjustments based on their personal experience or preferences. For example, some photographers often take less than 1 / 3-level exposure when shooting slides, while other photographers may add 2 / 3-level exposure when shooting with high-speed negative films.
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