I know, I know. You NEVER use on-camera flash. That's fine when you can control the environment. However, controlling the environment is sometimes harder than herding cats. Especially for me since I don't shoot in a studio. There are a couple of ways that I use on-camera flash to make better pictures. I'll show you how.
I take candid shots of people. Shots that a mother would love. Shots that are simply "Kodak Moments". Shots of personalities and memories. I don't have the opportunity to pose my subject. And, most of the time, I don't want posed shots. I just want to capture the moment or the personality. On-camera flash helps me and, even better, can help you make great pictures.
You should use flash when you shoot in bright sunlight. For example, the built-in flash on my Canon 30D has just enough power to soften harsh contrast and bring up shadow detail. You can adjust the ratio of fill flash to main light easily. Once set, the ratio is good for a series of similar shots. You don't have to change any other settings. Just compose and shoot as usual. The end result is better pictures in the camera. This shot was taken about 3 PM on the 4th of July in light about as contrasty as can be.
Getting good pictures when shooting in bars, banquet halls, and garages is difficult. The subjects are always moving and the light is variable and usually dim. If you use a built-in flash the results are ghastly – uneven exposure and harsh shadows. Using a Speedlite with direct flash is just as bad or even worse. Well, why not use bounce flash? Because it just doesn't work with high or dark ceilings. Using a brackets to hold the flash well away from the camera still makes harsh shadows and the bracket makes the camera harder to hold and shoot.
You can come close to the effect of off-camera flash and diffuse bounce light using a speedlite mounted directly on your camera. The technique I use works with both Canon and Nikon speedlite. The Canon speedlite has a diffuse reflector called a catchlight panel and an embossed panel called a wide panel. I use both. The Nikon speedlites I have checked have only a wide panel. A 3×5 card taped to the flash head is a good substitute for the catchlight panel. Here are the steps to follow.
Pull out both panels (or the wide panel and add a diffuse reflector). Tilt the flash head to 45 degrees to the lens axis.
Be careful of your focus indicators. Make certain the sparkle is on the right subject. You can make post processing much simpler by using fixed color balance, set to Flash. What this accomplishes is almost magic. For most shots, the major post shooting adjustment required is an exposure tweak. That is all I did to these two pictures.
Expect to take fewer pictures per battery set. Depending on how dim is the ambient light, you should get about half the shots you get with direct flash. Keep your spare charged batteries handy. Go! Shoot! Make those parents happy!