A softbox is essentially a reflective cloth material stretched over a frame that can be square, octagonal, rectangular, or long-strip rectangular.
Each produces slightly different light, and some professional photographers will only work with octagonal softboxes due to the more natural catchlight they produce in the eyes of a subject. Softboxes may cost more than umbrellas and take a little bit longer to set up, but the quality of light they produce is just about as soft as it gets. By carefully choosing the type, shape, size, and any accessories to direct the output, you can very effectively control the spread of light, too.
However, the downside is that you often have to be more conscientious in managing the contrast. You haven’t got the spread-around light of a typical shoot- through umbrella to help you, for example.
Typically, the reflective material inside a softbox is silver. Some manufacturers offer white-lined softboxes for a slightly softer light, though these do reduce the power of the light slightly. Most softboxes have an inner diffuser—essentially a piece of white diffusion fabric similar to the fabric in a shoot-through umbrella. This inner diffusion can usually be removed to provide a slightly harder light source, or to make the light more efficient if power is an issue.
The front of the softbox has a second diffuser. It is these two layers of diffusion and the lack of all-around spill light that provides a soft yet directional light source. On some softboxes, the flash is totally flush with the front of the box, and on others, it’s set slightly inside so that the edges of the softbox provide a small lip to stop light spilling around too much.
Many people point their softboxes directly at their subject, but the way a softbox works is that the light falls off gradually at the edge. You can use the light in this fall-off zone for a softer effect, which is called ‘feathering the light.’
The Flash Photography Field Guide is Adam Duckworth’s indispensable guide to getting the best out of your artificial light sources, whether you shoot with a simple light on your camera, a remotely-triggered unit, or a complete studio setup. Duckworth offers expert guidance on lights, supports, adapters, triggering, placement, and techniques, plus with comprehensive case studies, lighting diagrams and information on setups that will help you to achieve professional quality results using flash.