Softboxes come in all sorts of shapes and sizes but most of them work in the same way—the softbox replaces the reflector that would normally be fitted to the flash head, the light spreads around inside the softbox, bouncing off the walls and then hits an inner diffuser, a sheet of white translucent plastic, which evens out and diffuses the light. Then, in front of this inner diffuser is the front diffuser, which you can see in the picture. This diffuses the light even more. The walls of the softbox are typically a stippled silver material. Silver is highly efficient and the stippled surface helps to break up the light and spread it evenly. A few softboxes, including my Chimera, are also available with plain white interior walls. Plain white is slightly less efficient than silver (about 1/5th of a stop) and produces slightly softer light.
As you can see, the whole of the front diffuser becomes the light source so, if it’s close enough to the subject it can produce soft lighting with gentle shadows, and because the back of the softbox is enclosed there is no stray light bouncing around from the back.
Softboxes are simple pieces of kit but the differences in their design (and build quality) can be surprising.
The ideal softbox is one that allows the light from the flash head to bounce around and get thoroughly mixed up before it strikes the inner diffuser. Some of the better makes have an extra layer of diffusion (actually more of a central patch that partly reflects the light) to prevent hotspots and bounce some of the light from the center of the light back towards the light once more.
And what happens to the light once it reaches the inner diffuser? Well, in an ideal world all of the light should be forced to pass through the diffuser on its way to the outer diffuser, but some of the less well-designed models have a fairly large gap between the inner diffuser and the walls of the softbox, which allows some of the light to bypass the diffuser. The front diffuser is important too. The better ones tend to be thicker and denser than most. They still produce soft light but the light is crisper, better defined.
Some of the better-designed softboxes have a recessed front diffuser with a pronounced lip protruding from it, which helps to prevent unwanted light from traveling back towards the camera lens and causing flare. This lip also makes it easier to “feather” the light, i.e. to light the subject (or background) to create a graduated effect.
In theory, softboxes can be used with any type of flash but only lights that have removable reflectors can work really well, because with a fixed reflector in place the light tends to aim directly at the inner diffuser without first bouncing off of the softbox walls. A few hotshoe flashes are fitted with removable reflectors. Most are not, which makes them less than ideal. Softboxes can also be used with some kinds of continuous lighting too, although low power output and heat can be a very real limitation when using continuous lighting.
People argue endlessly about the “right” size or the “ideal” shape of softboxes but it’s really down to horses for courses when it comes to size and shape. Typically, if I was photographing a wine bottle I’d use a narrow rectangular (striplight) softbox to produce the shape of specular reflection (reflection of the light source) that suits the subject, and even though wine bottles are pretty small I’d use a 6’ high softbox so I could choose how large that specular reflection could be and how far away the softbox could be placed. Small softboxes often can’t be placed close enough to the subject to produce the effect needed.
If I was photographing a person full length [example below—links to larger image], I might choose a large rectangular softbox for the key light. For a headshot, perhaps a square or octagonal softbox, depending on the shape of catchlight that I wanted the eyes to show.
As you can see from the eyes of this portrait below [click on image to see a larger version], a square softbox can produce natural looking highlights in the shape of a window: “glazing bars” can easily be added by attaching black tape to the outer diffuser if required. The softbox was positioned in a fairly classic position—above and to one side where it produced lighting that is soft but without being flat.
Sometimes you may want a small softbox, especially if you’re shooting in a small room, because a small softbox will allow you to produce controlled, diffused light without it being soft. In a large room, a similar effect can be produced simply by moving a larger softbox further back.
One size and one shape of softbox cannot meet all needs. You really need several—but if budget and/or space is a problem, and you’re limited to just one softbox it’s generally better to get a large one and to be able to change the size and/or shape. Some softbox manufacturers supply removable masks that change the effective shape from square to octagonal. A more versatile (and cheaper) solution is simply to mask the front diffuser of your softbox to produce the size and shape you want, simply by temporarily fitting your own mask. The standard method is to fit blackwrap (Cinefoil) using clothes pins, but black trash bags will work too.
A lot of people mistakenly believe that the sole function of a softbox is to produce soft light—softboxes can do far more. In the “Black is Beautiful” [image below], I used two softboxes. They were both behind and to the side of my subject so that they lit the edge of her body and spilled some of the light across her back. The one on the right was higher because although I didn’t want to light the back of her head I did want to light her face. The important thing here was to get the lighting level the same on each side and to arrange both softboxes so that the light skimmed across my model’s back. Used in this way, softboxes can combine soft overall lighting with fairly hard local lighting or to produce low overall contrast and high local contrast.
There are other ways of getting soft light too. Any type of flash can be bounced from a white ceiling or a wall, which turns the ceiling or wall into the light source. There are also artificial tools such as lighting silks (basically just a diffusing material such as ripstop nylon or plain white shower curtain) that can be used instead of a softbox or umbrella or used in front of one to increase the size of the light source or to diffuse the light more.
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