The softbox might be the most popular studio light modifier, and for good reason. Photographers tend to think of it as portable on-demand window light. The most important effect a softbox has on a light source is to diffuse it, but it’s the softbox’s ability to contain extraneous light that sets it apart. Whereas the open design of an umbrella creates a lot of scatter—light moving in all sorts of directions, bouncing around the room and inevitably creeping into all elements of a scene—softboxes are opaque on all sides but one, delivering every ounce of light in one particular direction. Many softboxes also can be fitted with fabric grids to further limit scatter, effectively focusing the light’s output without compromising the diffused quality.
Softboxes also differ from umbrellas because they have multiple layers of diffusion; an internal baffle softens the light before it reaches the front silk. This helps eliminate hot spots and makes for more even output. Of course, photographers who like to experiment with their softboxes can remove one or both baffles, amplifying the specular qualities of the light, creating deliberate hot spots and, ultimately, making contrastier and more specular output. If the softbox has a silver interior, this “punchy” quality is already amplified, whether or not the diffusers are removed. Silver interiors boost contrast, great for a glamour look.
In softboxes, as in life, size really does matter. A small softbox (under 24 inches or so) is okay for small subjects and headshots, but the soft light just can’t spread far enough to evenly cover waist-up portraits or other subjects of size. Conversely, the bigger the softbox, the more the light is able to spread, and the more it also becomes capable of wrapping around edges, creating softer transitions between shadow and highlight. This look is great for high-key portraiture of children and families, and even fashion and beauty images.
Another benefit of a big box is that it remains large in proportion to the subject, even as it’s moved away. Since a bigger source maintains its softness over longer distances, a big box is ideal for large scenes like industrial images or group photos.
The oft-cited reason photographers choose octagonal softboxes (otherwise known as octabanks, octodomes or octas) is that these modifiers create more appealing round catchlights in the eyes of subjects. But when you’re talking about the biggest octas, you also get the benefit of a huge source that wraps around edges for a supersoft transition into shadow. That broad source also makes for less dense shadows and slightly less contrasty output. One could interpret that look as too flat, so if what you’re hoping for is more punch, look for an octa with a shiny interior, or one that aims the strobe head outward to the front silk rather than aimed in reverse at the back of the box.