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Old 01-12-2007, 01:07 AM
Dennis
Dazzled by the Cosmos.

Dennis is offline
 
Join Date: May 2005
Location: Brisbane
Posts: 11,820
In the good old days of 35mm film photography, a "slow speed" film was 25 ASA, a "medium speed" film was 100 ASA and a "fast film" was 400 ASA. So, when there was lots of light available, you would normally select a slow to medium speed film and in dimmer conditions, select a faster film, right up to the very grainy Konica 3200 ASA film. Examples of film I used to use were:
  • Kodachrome 25 - a 25 ASA slide film.
  • Kodacolor 100 - a 100 ASA print film.
  • Fujicolor 400 – a 400 ASA print film.
  • Ilford FP4 - a 125 ASA B&W film.
  • Ilford HP4 - a 400 ASA B&W film.
The grain (film structure) was very fine at 25 ASA and much coarser at 400 ASA, giving a 400 ASA photo a gritty look, much like noise in short exposure CCD image. You could enlarge a 100ASA film to produce a 16x12 inches print before the grain became noticeable, whereas grain would show at 10x8 inches from a 400ASA film negative.

Films improved over the years and a 1990’s era 400 ASA film had grain as fine as a 1980’s 100 ASA film. Generally, CCD’s with small pixels are “slow” whereas CCD’s with large pixels are “fast”; that is, they can record in dim light more efficiently.

Cheers

Dennis
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