“Film Speed” refers to the sensitivity to light of the film. “Fast” film is more sensitive whilst “Slow” film is less sensitive.
Slow films have lower ISO numbers such as 50, 125, 160 are all slow or relatively slow. Fast films have higher ISO numbers such as 3200, 1600, 800. ISO 400 is considered “everyday”. Read on to know more…
Fast film means that you can keep using faster shutter speeds as the light fades. Thats because its more sensative to light, its fast. It takes less time for it to record the image.
Slow film is the opposite. When the light fades the film will need a slower shutter speed than a fast film in the same light. Simple as that.
A good way to realise this is with a light meter. If you press the button to take a recording and then rather than alter the Aperture/Shutter Speed, alter the ISO and you will see that the Aperture/Shutter Speed change accordingly.
So what’s the point to all this anyway?
You need to consider the “grain” and “quality” of the film.
Slow film is of better quality because there is finer grain (you can’t see the grain). The compromise is slower shutter speeds, i.e. you have to use it in stronger light.
Fast film is of worse quality as the grain is more visible. Its grainy. But you can hold the camera in your hands and photo in low light.
TIP: its all made redundant somewhat if you use a tripod. You can use a slow film (e.g. ISO 125) in total darkness if you like, it doesn’t matter.
You would use a slow film in a studio and when you want top notch images. You would use fast film if you photograph in low light conditions, holding the camera in your hands. Fast film is for variable and unknown light conditions. Slow film is for controlled light conditions and when you have a tripod.
Sometimes I will use a fast film even if the light is strong enough for a slow film, for arty reasons. It can look very cool to have grainy images. Much in the same way you use contrasty film. Contrasty film is cool too.
So, in conclusion, mix and match and think aesthetically as well as practically. What look do you want, what quality and how are you going to use it.
EXAMPLES (120 and 35mm)
- Ilford FP4+ 125 (B&W – medium contrast)
- FujiColor Pro 160 S or C (Colour - more contrast than kodak in general, “S” for Skin and “C” for Contrasty)
- Ilford Delta 100 (B&W – low contrast)
- Fuji Neopan 1600 (mega contrast and grain)
- Kodak Portra 400 (Colour)
Hope this helps,