When photographing candids in a dark environment, there are many options for lighting. One could choose to use the camera’s built-in flash, but that gives harsh shadows and terrible red eye. Adding a speedlight (flash) to the hotshoe and firing it directly moves the light source a bit off axis, but shadows are still harsh and red eye is still a risk. Diffusing the light, say with a Gary Fong Lightsphere or a Lumiquest Softbox (both of which mount directly to the head of the shoe-mounted flash), helps too. However, the light is still on axis.
A very common solution, and one which I often use, is to tilt the strobe head up and bounce it from a ceiling or wall. This effectively provides a large off-axis light source, giving a very soft fill. However, if the ceiling is quite high, non-white, or not there at all bouncing just won’t work. Even if bouncing does work, the fill is still quite soft and undramatic.
A lighting solution that I’ve been working with for the past while is to hold the flash in one hand while shooting with the other. I put a diffusion on the flash, usually a Lumiquest Softbox LTz and hold it with my left arm outstretched at about 30 degrees from horizontal. This method gives soft (but not too soft) off-axis light that is easily under my control.I trigger the flash (Nikon SB-900 or SB-700) using Nikon’s CLS (Creative Lighting System). I set the camera’s built-in flash as a “controller” so that it will control remote flashes but not add to the exposure. If I had set it to be a “master” it would fire as part of the exposure. I then set the handheld flash to be a remote, making sure that both it and the built-in flash are set to the same channel and group. (Note: Nikon CLS isn’t actually that complicated once you figure out all of the terminology. I found this site to be extremely useful.)
Of course, having more than one light source usually improves a photo even more. In the case of a wedding I did this fall in a barn, the light shining through the windows and poking through cracks in the wall provided an excellent backlight to complement the light from my flash. Thanks for reading!