Theory is all very well in……….……err! theory. There are times however when creativity demands that theory can take a back seat. Theoretically there is a correct exposure for any given shooting situation.
The histogram of a ‘typical’ image usually has a wide spread of tones.
The ‘sunny f/16’ rule is based on this assumption (the basic idea is that on a sunny day the correct shutter speed, with the aperture on your camera to set f/16, is roughly the same as the ISO used). The ‘sunny f/16’ can be expanded to work out the exposure for other conditions too. In fact with a bit of searching on the Internet it’s possible to find tables of exposure settings that cover every eventuality (Fred Parker’s Ultimate Exposure Computer is a particularly useful resource).
Who wants to be correct all the time though?
High and low-key photography are styles of photography that require a slight bending of the rules. First though you need to know the rules… A photograph is essentially a range of tones from dark to light that form an image. Typically the key tones are mid-tones (subjects such as grass or rock for instance). Camera exposure meters are calibrated to average out the exposure to an overall mid-tone. A high-key image is one that has been exposed so that the key tones are lighter than this mid-tone ideal. This means that shadows are brighter and more open and the image usually has a light airy feel. Conversely a low-key image is one in which the key tones are darker than the mid-tone ideal. This makes the highlights dimmer, the shadows dense and the overall image looking darker and more brooding.
This is a high-key image. Virtually all the tones in the image are lighter than a mid-grey. The background was lit by a lightbox to make it as bright as possible.
Theoretically (there’s that word again) all you have to do to achieve a high or low-key effect is over or underexpose your images respectively. In practise however, it’s all too easy to clip the highlights or shadows. This results in a loss of detail that can’t be recovered. However, it’s fun to experiment shooting this way. As long as you don’t push the exposure too far it’s possible to create very acceptable results.
Shooting this low key-key product shot involved stopping light falling on the background and precisely directing light onto the camera.
For full control over your high and low-key images you need to modify the light that falls onto your subject. For high-key images this means pushing more light into the shadows. At its simplest this can be achieved by using a reflector or two (the least expensive option being white card, though commercial reflectors give more consistent results). A slightly more complex method is using additional lighting such as flash or studio lights to lighten the shadows. Low-key images require the opposite: actually blocking light from reaching certain areas of the subject. This can be achieved by sheets of card again or by fitting snoots and barn doors to your lighting (a snoot is a tube that directs the light from a flash or studio light, a barn door is a set of four flaps that can be opened or closed to precisely direct light).
The key (hah!) in both instances is interpreting the camera’s histogram so that you’re confident that the desired effect has been achieved. Do that and I’m sure you’ll be impressed with what you’ve accomplished. Well, theoretically.
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