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When photographing subjects against the direction of the light, contrast may exceed the latitude of the film sensor. An averaged exposure measurement is a good compromise but may not solve the problem. Detail may still be lost, particularly when using colour film with limited dynamic range. The advice normally offered is to increase exposure, by either selecting a larger aperture or a slower shutter speed, to avoid pictures being too dark. Exposure meters compensate for a bright background by reducing exposure and trying to find a compromise that suits both the brightly-lit areas and the shadows. However such compromises may not work. If the exposure is set for the highlights, detail may be lost in the shadows. If it is set for the shadows the highlights may burn out.

To ensure that all the detail in a high-contrast scene is rendered satisfactorily it is necessary to reduce the contrast. One way to do this is to soften the primary light source with a diffuser. This is routinely done in studios by using softboxes on the flash heads, but the same principle can be employed elsewhere. In the case of windows, net curtains soften shadows and reduce contrast considerably. Outdoors, a sun sail can be used. This is a 2 x 2m square of fine-mesh white material, such as tulle, supported by long poles. Introducing this between the sun and the small subject such as a person is surprisingly effective if somewhat inconvenient.

Daylight fill-flash is another useful technique for reducing contrast. A dedicated flashgun equipped with a small softbox provides a reasonably diffused controllable light source to fill dark foreground shadows. The basic principle of fill-flash is to adjust flash output to balance the ambient light. Foreground subjects and shadows are consequently illuminated to match the wider scene. However, this can produce a rather brash unnatural images. More subtle effects may be realized by using flash compensation, for example, by reducing the power of the flash by one or two stops (halving or quartering the output). Precise levels of fill and compensation must be decided with knowledge of the basic flash strategy used by a particular camera. They are also dependent on ambient light, contrast, film latitude, the nature of the subject and the type of image required.

The use of fill-flash implies a number of limitations on normal camera operation. The recharging cycle of all but the most sophisticated flashguns will be much slower than motor-driven film transport so firing rate must reduce. But, more significantly, it is necessary to keep the shutter speed below the camera's flash synchronization speed. Above this speed the trailing blind of a focal plane shutter begins moving before the leading blind has stopped. Exposure is achieved progressively as a narrow opening between the shutter blinds sweeps across the frame. Consequently only part of the frame will be exposed to the comparatively brief burst of flash. This limitation imposes a corresponding restriction on aperture, and hence depth of field.

A similar fill effect can be achieved with reflectors of various types. Gold and half-gold reflectors return warm light appropriate for skin tones, whereas white surfaces produce a cooler effect. Reflectors are easier to use than flash in the sense that their effect can be seen and adjusted before the shutter is released. But in practice they are cumbersome, need to be held in place and tend to attract attention.


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