film iso and asa speeds

[electricalperson]

can anybody explain to me what the speeds of film mean?

i noticed a lot of professional quality film is iso 50 - 100 and the stuff at cvs is 200 - 800

 

[Josh66]

Film speed - Wikipedia, the free encyclopedia
That should explain it in as much detail as you care to read.

Basically..., ISO/ASA is the film's sensitivity to light. "Fast" film has a higher sensitivity to light (higher ISO). It is fast because with it being more sensitive to light, you can use a faster shutter speed to get the same exposure as a slower film would get you under the same light.

 

[christopher walrath]

OK, lemme esplain. . .

First ASA (American Standards Association) and ISO (International Standards Organization) are one in the same just one is the progenitor of the other. SAME GIRL DIFFERENT SKIRT.

Don't let a film's speed (sensitivity to exposure from light) fool you into thinking it's good or bad. Fuji Velvia is rated ISO50. Great color reversal film. Kodak TMax P3200 (ISO 3,200) is just as good for low light photography in Black and White. The reason most of your house brands lie between the ranges of 200-800 are not because those films are substandard. It is because they get one film made. Drumroll please. . .

ISO400.

See, it's not the film that the camera detects to determine film speed. It's that little black and silver box code (DX code) on the side of the cannister. The house brand ISO 400 film has cannisters with a ISO400 DX code on them. The house brand ISO 800 film has ISO 400 film in the cannisters marked with an ISO 800 DX code. The ISO 200 house brand film has ISO 400 film in the cannisters that are marked with ISO 200 DX codes.

See, some photographers mess with push/pull processing which means that they intentionally increase or decrease exposure for a given situation. And since film has this ability to be pushed and pulled they have made cannisters that fool your camera into thinking it has three ISO rating's to choose from, taking this forgiveness of film into consideration.

 

[Early]

Also, the lower the film speed, the smaller the grain, and visa versa. Generally speaking, of course.

 

[kevin_c]

THIS may be useful, although it does start getting a bit technical.