All film has a speed rating - even digital cameras use the common ASA speed index. Slower films produce sharper images but require large amounts of light. Fast films can be used in low light situations in exchange for an increase in contrast and noise/grain.

speed rating sensitivity contrast grain
50 ASA
low
low
low
100 ASA
medium
medium
medium
200 ASA
medium
medium
medium
400 ASA
high
high
high
800+ ASA
very high
very high
very high
  • 50ASA is slower than 100ASA, and requires 1 stop more light
  • 400ASA is faster than 100ASA, and requires 2 stops less light

Sometimes using a faster film speed is the only way to get a sharp image. Try the following example to learn how shutter speed, aperture, AND film speed all use the interchangable photographic "stop".

 

SimCam Film Speed Example:
First set both SimCams to 1/60 f4 and shoot a picture. The 400 ASA film is overexposed, so you need to compensate by reducing light - move the shutter or aperture 2 stops higher to balance the exposure. (For example move the shutter to 1/250, or the aperture to f8)

All stops are interchangable. By going from 100ASA to 400ASA, you have two stops more light. You can "spend" those stops on aperture or shutter speed.

Notice the increased grain and contrast of the 400ASA example. Remember, if you need more light than, you can increase the film speed.

100ASA Film 400ASA Film
Shutter:
Aperture:
Shutter:
Aperture:
final exposure: final exposure: