When measuring light and setting exposure in professional photography, several key factors must be considered:
- Lighting: Assess the intensity and distance of the light source, accounting for any light loss due to diffusers, acetates, or atmospheric conditions between the source and the subject. Ensure the brightness range (contrast) remains within the film’s tolerance to capture full detail.
- Subject Properties: Evaluate how much light the subject reflects, considering its tone, color, and surface texture, from a black cat in a coal store to a milk bottle in the snow. Since the light meter cannot identify the subject, interpret the readings to accurately record both light and dark subjects.
- Film Speed: Consider the ISO speed rating along with any necessary adjustments due to the film’s color sensitivity relative to the subject light source or for extremely long exposure times, keeping in mind reciprocity failure.
- Unusual Imaging Conditions: Account for light absorption due to lens filters and attachments, or a dimmed image caused by extending the lens for close-up focusing.
Additionally, important interpretative or subjective considerations come into play. Decide whether to expose for the brightest parts of the scene, rendering darker parts black, or to expose for shadows, allowing light parts to ‘burn out.’ These decisions involve overriding the camera’s automatic settings.
The chosen exposure is delivered to the film by a combination of:
- Intensity (image brightness): Controlled by the lens aperture, which also affects depth of field and, to some extent, definition.
- Time: Controlled by the shutter speed, influencing the reproduction of subject or camera movement and the spontaneity of expression or action.
For instance, when photographing a subject moving parallel to the camera lens, depth of field plays a crucial role in keeping the figure in focus across various settings. Using a tripod for the camera minimizes shake at slow shutter speeds. The effect of different shutter speeds will be evident in the final photograph. Faster shutter speeds freeze the action, while slower shutter speeds result in a blurred subject.
In everyday photography, you may not encounter such extreme subjects frequently, but you will need to balance time and intensity, deciding whether depth of field or movement is the primary concern.
