The sensitivity of different printed films

Different films may have different sensitivities to light, that is, some films will require more or less light than others to achieve normal exposure. A film that requires less light is called a High Speed ​​Film, whereas a film that requires more light is called a slow film or a medium speed film. The sensitivity of the film to light is called FilmSpeed ​​or Sensitivity.

However, it must be emphasized that the so-called speed of film is not related to the usual speed of sports. Film speed only involves the sensitivity to light. However, due to the high-speed film has a strong response to light, in the same aperture, you can use a higher shutter speed, to shoot higher, to shoot high-speed action, so some filming friends misunderstanding high-speed film is used To shoot high-speed action film.

Film speed has had 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 world uses the international standard ISO, but in fact, there is no difference between the ISO and the previous ASA. For example, In the past, ASA 100 and others, such as DIN 21, were originally known as ISO 100/21, but they have now been simplified to ISO 100. In other words, DIN has been eliminated, and ASA has changed its name to ISO.

The ISO speed of each film is provided by the film manufacturer and noted on the packaging. The higher the sensitivity, the faster the film - the greater sensitivity to light. ISO's series are ISO50, 100, 200, 400, 800, 1600 and 3200. ISO200's film sensitivity to light is one level higher than ISO100 film, while ISO800 is two levels faster than ISO200, and so on.

For example, the ISO800 film ISO100 level three, which means that if you use the ISO800 film to shoot a scene, the exposure combination used is 1/1000 seconds and f/8, then the same scene with ISO100 film will need to increase the three aperture , that is 1/1000 seconds, with f/2.8 to get the same amount of exposure, calculated with the same example, if you use ISO400 film, what aperture will you use at 1/500 second shutter speed? That's right, it's still f/8.

What is the significance of the ISO sensitivity marked on the film box to you? It actually tells you how much exposure the factory recommends to get a photo of "correct exposure" on the film.

You can adjust the ISO speed noted on the film on the camera. The camera's metering system will use the film's suggested exposure as the exposure. However, due to the different characteristics of the film, the photographer also has some exposure. Like it, some photographers will make adjustments based on personal experience or preferences. For example, some photographers often fail to shoot 1/3 of the slides. Some photographers may take 2/3 exposures when shooting with high-speed negatives.