When you need to add light to a setup, the most available source is the flash that's built into your camera. Almost every digital camera comes with a small built-in electronic flash that is tied into the autoexposure system. Because of its limitations, built-in flash is not recommended for studio photography. In most cases you just need to know how to turn it off so it won't flash unexpectedly. However, there may be times when you can use it successfully, especially for fill flash on non-reflective subjects. When using the built-in flash, there are a few concerns:

• Because they are so small they also emit a hard, direct light and can't be rotated to bounce flash off a wall or other reflective surface to diffuse and soften it.
• Because of the head-on position of the flash, the light casts no shadows on the subject to add texture or volume. However, they will cast a shadow behind the subject if there is a background.
• When you get close, the lens on some cameras blocks the flash and casts a shadow.
• Some built-in flashes overexpose foreground subjects when they are too close. A few cameras let you vary the flash intensity if this happens.

  When you use the built-in flash, or an external flash designed to work with the camera, you control both with the camera's flash settings. These usually include the following:

• Autoflash fires the flash whenever the light is too dim to take a photo. This is the default mode for most cameras and flash units and at times you may even be surprised when it fires.
• Fill Flash (also called flash on, forced flash, or anytime flash) fires the flash regardless of how much available light there is. Some cameras can even identify backlit subjects and fire the flash so they don't appear as dark silhouettes against a bright background.
• Red-eye Reduction fires a separate lamp to reduce red-eye when taking portraits. Red-eye is caused by light from a flash reflecting off the red retina at the back of the eye, back to the camera. This mode fires a short preflash lamp or a burst of flashes to close the iris a moment before the actual flash fires to take the picture.
• Flash Off or Flash Cancel turns the flash off so you can photograph without the built-in flash firing. This is the mode you'll use most often in studio photography, especially when using other lights to illuminate the setup.
• Slow Sync (sometimes called night, night scene, or night portrait mode) keeps the shutter open longer than usual to lighten the background.