Absolute Beginner's Guide to Digital Photography

CHAPTER 3 FILM BASICS 37

The higher the number in a given system, the faster the film—and the less light you

need for a correct exposure (see Table 3.1). An ISO or EI or ASA 200 film is twice as

fast as an ISO 100 film (one stop faster), half as fast as an ISO 400 film (one stop

slower). For a correct exposure, the ISO 200 film needs half as much light as (one

stop less than) the ISO 100 film, twice as much light as (one stop more than) the ISO

400 film.

Table 3.1 Film Speed and Shutter Speed

Film Speed Sample Exposure

ISO 100 f/2.8 aperture at 1/30 sec shutter speed

ISO 200 f/2.8 aperture at 1/60 sec shutter speed

ISO 400 f/2.8 aperture at 1/125 sec shutter speed

ISO 800 f/2.8 aperture at 1/250 sec shutter speed

ISO 1600 f/2.8 aperture at 1/500 sec shutter speed

ISO 3200 f/2.8 aperture at 1/1000 sec shutter speed

Film speed influences heavily how the film is used. Sports photographers that still

shoot with film must use high-speed film because higher shutter speeds capture

motion with no blur. Slower film speeds are used for portrait photography because

maximum clarity is desirable (see Table 3.2).

Table 3.2 Some Typical Film Speeds and Their Uses

Film Speed Uses Grain

Slow: ISO 50 or less Brightly lit subjects Finest grain

Medium-speed: around General outdoor use Medium-fine grain

ISO 100

Fast: around ISO 400 Indoor or dimly lit scenes, Medium grain

bright scenes with fast

moving subjects

Extra fast: more than Very dark scenes, especially Coarsest grain

ISO 400 with moving subjects

Film Speed and Grain

The faster the film, the more visible its grain (see Figure 3.3). The light-sensitive part

of film consists of many tiny particles of silver halide spread throughout the film’s

emulsion. A fast film is fast because it has larger crystals than a slower film. The