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Each classification will have different speed, lighting type, format, packaging, etc. Reversal films use a reversal processing method to bring out a positive image instead of a negative image. Reversal film can be used on projection, display, movie, and industry use. Improper lighting will deviate from realistic colour much more severe than a human eye can observe. You can experience this trouble by taking an indoor picture without an electronic flash. Most general-purpose colour films are colour corrected for daylight. Most colour movie films are colour corrected for tungsten lighting. Film speed has been defined by International Standards Organization as ISO.
No, high-speed film is very grainy, foggy, poor colour reproduction, low contrast, short shelf life, etc. If you are right, why is it the film manufacturer promote high-speed film? Film manufacturer would like to do more research on high-speed film, therefore, they have to sell more to support their dream. For high quality job, such as product shoots, use ISO 25 or ISO 50 speed film. For softer contrast, such as portrait, wedding picture, use ISO 160 speed film. Please compare with the right side portrait, which was taken with ISO 160 professional film. Contrast, colour quality and shelf life are inversely proportional to speed. Theoretically, the lower the speed, the better quality you could get.
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