As much as I don't like using on-camera flash very often, there are times when you're in a relatively dark room and you have no choice. And for the most part built-in flash does a respectable job of lighting nearby scenes. It's especially useful when you're taking people shots indoors. One danger of using flash indoors though is that flash will bounce back from any reflective surface, such as mirrors, windows and even shiny painted surfaces.
Flash reflections are not only distracting (it looks like a car headlight outside the window in this shot) but they can fool your camera's meter into underexposing the main subject. (In fact, I had to lighten this shot in Photoshop just to get some detail back in the faces.) Because the reflective surface is a far more efficient reflector than your "average" subject, it reflects back much brighter. The meter sees that bright light and thinks the entire scene has enough light.
You can avoid flash reflections easily by just being careful about what's behind your subjects. If there's a window or a mirror, for example, just alter your shooting position a bit so that you're not firing the flash right into the surface. If you can't get rid of a window, try just closing the curtains or the blinds. If I had closed the blinds all the way for this shot I probably would have still had a bright highlight, but it would have been much more subdued. Another option, if you have an accessory flash unit that has a bounce feature, is to tilt the flash head up and bounce the flash off of the ceiling (provided you have a white ceiling at normal height). The ceiling will act as a big diffusion panel and not only prevent flash-back, but also soften the overall light.
Friends in Beijing
9 hours ago