What is reversal film (slide)?
Most film after developing will bear a negative image. 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.

What are daylight and tungsten type film?
Colour films are very sensitive to the quality of light. 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. With tungsten lighting, your pictures appear yellow. With florescent lighting, your pictures appear green. Electronic flash is corrected to same light quality as daylight. Most general-purpose colour films are colour corrected for daylight. Most colour movie films are colour corrected for tungsten lighting.

What is the speed of film?
Speed of film is the degree of light sensitivity of the emulsion. Film speed has been defined by International Standards Organization as ISO. ISO 100 film is general-purpose film. ISO 200 is medium speed film. ISO 400 up is high-speed film.

What is DIN?
DIN is the German standard of defining film speed.

How do we compare film speed?
ISO is a linear number. For example, ISO 200 is twice as fast as ISO 100. ISO 400 is twice faster than ISO 200. DIN is based on the logarithmic of numbers; every 3 DIN is double the speed.

Should I use high-speed film more frequently?
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.

What is grain?
Emulsion contains crystal. Larger crystal is more sensitive to light. Crystal or grain will be visible if the negative is enlarged.

What type of film should I use?
For high quality job, such as product shoots, use ISO 25 or ISO 50 speed film. For general-purpose, use ISO 100 speed film. For softer contrast, such as portrait, wedding picture, use ISO 160 speed film. For poor lighting conditions, use ISO 200 up.

Left side picture was taken with ISO 50 high contrast film. Please compare with the right side portrait, which was taken with ISO 160 professional film.

Why low speed film has higher quality?
Contrast, colour quality and shelf life are inversely proportional to speed. Grain size, fog is proportional to speed. Theoretically, the lower the speed, the better quality you could get.