Virtually all modern small and medium format cameras are equipped with integrated systems to measure the luminosity of the subject’s light, thereby evaluating the correct exposure.
This functionality operates either by manually adjusting an appropriate combination of f-number and shutter speed or by automatically setting:
- The correct shutter speed for a pre-adjusted aperture;
- The appropriate aperture for a pre-set shutter speed;
- An optimal combination of shutter speed and aperture adjustments selected by the system as part of an integrated program.
A small, light-sensitive sensor can be placed at the front of the camera housing, near the lens, or positioned inside the camera, sampling light that has passed through the lens. In both locations, the sensor must measure light through any filters used on the lens.
An internal sensor system is more precise and performs consistently when changing lenses. All modern exposure measurement systems require battery power, typically sharing the same power circuit with autofocus, shutter synchronization, and the film transport mechanism.
You may need to adjust the film sensitivity (ISO speed), although many 35mm cameras do this automatically by reading a barcode on the cassette through electrical contacts in the film compartment.
Large format cameras rarely include integrated light measuring devices, necessitating the use of an external measuring device or manual calculations instead.
