Speedlights and on-camera flashes have become so advanced that many photographers are using them as primary studio and location lights. Thanks to wireless communication, multiple flashes can be used together in several groups to produce very sophisticated lighting setups.
Just as adding more flashes will give you exponential lighting possibilities, working with light-modification tools will give you even more ways to control, shape and build your light. These tools are important because your flash is a highly directional light source. When used without any modifiers, a flash produces scenes with very heavy contrast. Your subject is lit from a single direction while the rest of the scene is dropped into shadow since the camera meters for the flash burst.
To wrangle the harsh unidirectional light output of a flash, diffusers are a class of light-modification tools that soften and spread light by passing the output through semitranslucent materials. Keep in mind that diffusion reduces the amount of light from your flash, and the material that you’re using can also influence the color temperature and texture of the light.
The most popular diffusion system is the softbox, which offers a front panel of white see-through material on a housing that usually includes a reflective interior for channeling as much light spill from the flash forward as possible. The result is softened wraparound light that’s very flattering for portraiture, much like natural daylight through a window on a cloudy day. Many softboxes are available with removable interior baffles for diffusing light further. Octaboxes offer a similar construction with a wider, more circular shape for a larger spread of light and rounder reflected catchlights in the eyes.
Umbrellas are particularly popular with speedlight users because the results are very much like a softbox, and setup is even faster and easier. Umbrellas produce more side spill, however, and because of this, you often lose more light from your flash. They’re usually more affordable than softboxes, as well.
Beauty dishes are a good intermediate choice because the open-face design, coupled with a reflective half-moon interior, diffuses at the same time that it channels light forward. The results are much like an umbrella with soft light that wraps around your subject. Beauty dishes are popular in fashion and portraiture for their lively catchlights.
Domes are great diffusion solutions for on-camera flashes during events because they soften the highly directional output, and produce candids and portraiture with a more natural overall light spread that’s similar to bouncing the light from a nearby wall or ceiling. They don’t channel light forward, however; light rays are distributed along the circular circumference of the globe and become more omnidirectional. Domes can reduce light output quite a bit and are better for working at close distances.
Silks or even semi-opaque fabrics and other materials can be placed in front of lights or hung just off-frame for adding texture or reducing light. Silks must be mounted to a frame, stand or other device, but they’re not limited by the shape of your light modifier, so they’re very versatile for placement. They can also be used as background material with a large enough panel.
Most modern flash designs include a swiveling head and small bounce card for diffusing light output by bouncing it off of a wall or ceiling, which spreads light rays more evenly through a scene. For finer control, you can use much larger reflectors and bounces in a large variety of different materials, sizes and textures.
These different constructions will influence the reflected light. A silver bounce, for example, is highly reflective, and the light will be very bright and specular like a mirror. Gold, on the other hand, introduces warmth to the reflected light, making it an ideal tool for adding an afternoon glow to portraiture. White bounces are available (you can also use bright white posterboard), but they’re not as specular as silver, so the light produced is softer and more diffused for a natural daylight feel. Reflectors and bounces are often malleable for more control over the shape of reflected light and are typically designed as quick-twist round panels that can be handheld or mounted to a stand.
Grids and snoots control rays of light by channeling them. Grids have a namesake "grid" that’s placed directly in front of the light, which is channeled through these grids at a straight angle. This eliminates side spill for stronger contrast and a more direct throw. Be wary of cheaper models, as thicker grids will show a patterned grid of shadows in the light.
Snoots are highly directional, even more so than your flash. They provide so much contrast that they result in a spotlight effect with extreme natural vignetting around the light. Snoots are often too powerful, so there are many models that will allow you to shape the front cone for more or less light.
Though they have less application with the small form factors of flashes, there are also tools to shape light by blocking it. In studios, C-stands and gobo heads are used with extension arms to add light blockers like flags and cutters, which are usually constructed from black fabric or metal to absorb light spill and add shadow, useful for thinning faces and bodies in portraiture. They’re also used to prevent directional flares from entering the camera lens from your lights. This gives you a way to control subtle spills of light at the same time that it gives yo
u the ability to keep one portion or subject illuminated differently from another in your shot. Scrims are similar to silks, only they reduce or block light like a flag as they’re made from much thicker materials. Like silks, the advantage is versatile placement.
Cucosloris tools, also known as "cookies," are flags with patterns cut into them in order to facilitate fake shadows or silhouettes, like tree branches or other textures. Gobos are similarly patterned cutouts that are placed within the light housing or directly affixed to the front of a light.
Finally, gels give you a way to produce in-camera color effects while also providing a solution for working under off-white or mixed-lighting situations. The most popular gels for camera flashes are CTO (orange) for matching flash output to tungsten and halogen lights, and Plus Green for working under fluorescents. CTB (blue) will correct your flash output for areas where you have a heavy blue shift like shade. Gels are available in varying strengths as well as kits.