Flash. The bright light that blinds you before the picture is taken and leaves you and your family/friends looking like a bunch of Hellspawn on
a bad day. Sort of like this...
Well, did you know that flash can be your best friend instead of your worst enemy? It's true! Flash, when used in certain ways, can generally brighten up a dark scene or illuminate objects hidden by shadow, especially when outside!
Some general tips about flash and red-eye
Light gets dimmers the farther it travels. The same is true about flash. So subjects close to the flash when it goes off will be lit up while subjects farther away will be darker or hidden in shadow.
A flash-lit scene may not be evenly illuminated. To solve this problem, use a smaller aperture for subjects close to the flash and a larger aperture for subjects farther away.
Since flash is so quick, it usually catches an object in motion so you don't have to worry about anything blurring, though it's hard to tell what the subject looks like when lit.
Red-eye is the reflection of the eye's retina through its lens. It usually occurs when the flash is mounted too close to the camera's lens.
To avoid the red-eye effect, DO NOT take pictures of people or animals using flash while in dimly-lit room. Though most digital cameras today come with a setting to correct red-eye.