Understanding the SLR Camera

The most important technical step to a good print is a good negative. The key to a good negative is correct film exposure.

Three variables control film exposure:

• Lens Opening
• Shutter Speed
• Film Speed

Lens Opening:

1. The larger the opening, the greater amount of light that reaches the film.
2. The size of the lens opening is measured by f-stops. ( The larger the f-stop, the smaller the opening )
3. The f-stops are as follows:
   • f 1.4 ( most light )
   • f2
   • f 2.8
   • f4
   • f 5.6
   • f8
   • f 11
   • f 16
   • f 22 ( least light )

Shutter Speed:

1. The time for which film is exposed to light is controlled by the shutter speed.
2. The faster the shutter speed, the shorter the duration of film exposure, and the less light reaches the film.
3. A dimly lit subject requires a slower shutter speed than a brightly lit subject.
4. The following are shutter speed settings: ( fraction of seconds )
   • 1 ( most light )
   • 2
   • 4
   • 8
   • 15
   • 30
   • 60
   • 125
   • 250
   • 500
   • 1000 ( least light )
5. Each setting represents a halving or doubling of light that reaches the film. For example, 1/8 allows light in for twice as much time as 1/15.

Film Speed:

1. The third film -exposure control is film speed, or the sensitivity of film to light.
2. Fast films receive and record light more readily than slow films. ( The terms fast films and slow films should not be confused withfast or slow as it applies to shutter speeds or lens.)
   Example: Imagine two strips of film, one with a fast speed and the other with a slow speed. If both strips are exposed to equal amounts of light, upon development the fast film will produce a greater density than the slow film.
3. A fast film is needed in a dimly lit room to capture the little light that exists.
4. A slow film is adequate for brightly lit subjects where light is plentiful.
   Fast films have emulsions that consist of larger silver crystals than slow films. These crystals when exposed and developed, clump together to create the density that makes the image. These clumps are referred to as grain, and look like fine particles of sand. Grain can make the picture look fuzzy or course. The faster the film speed, the courser the image.
5. The following is a chart to determine film speed and its use:
   • 32 ISO – Slow film; best with brightly lit subjects; produces very fine grain negatives.
   • 125 ISO – Medium speed film; best for general outdoor use; produces medium fine grain negatives.
   • 400 ISO – A fast film; best for indoor or dimly lit subjects, though can be used outdoors; produces acceptable, but coarser grain than slower films.

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