Digital cameras flash units come in many shapes and sizes. Low end digital cameras include low energy built in flash units. High end digital SLR cameras can support sophisticated external flash units which can provide superior lighting in difficult scenarios. Here are some basic facts about flash units both built in and external.
Flash units came a long way since their early days. Back then flash units were using powder that was lit by electrical current and literally "blew up" to produce the light energy. Using these flash units was a risky business. It was also difficult as the flash units were not automatically synchronized to the camera's shutter. The photographer had to make sure that the flash goes off at the exact right time synchronized with the shooting of the photo.
The flash units of today are highly developed technology devices. The flash and camera are automatically synchronized using an electronic flash tube taking all of the pressure off of the photographer. Digital cameras today can determine themselves if a flash is necessary, can set their own intensity and other parameters and can trigger the flash at the precise tine the shutter is opened. All of this is done in the background with no manual effort. For those scenarios calling for a more hands on approach, digital cameras also include a manual mode where the user can set all of the same features to their specifications.
Flash units are separated into two basic categories: Internal built-in flash units or external flash units. Internal flash units are naturally built into the camera. Nearly all digital cameras come with such a unit and permit the user some control over it through the camera's menus and buttons. External flash units are attached to the camera's body through a dedicated slide-in slot or by using an electrical cable. Not all digital cameras can support external flash units. Generally the lower end pocket cameras do not support external flash units while all high end digital SLR cameras will. There can be quite a bit of difference in external flash units. They can have different light energy levels that they can emit and different mechanical characteristics. Some external flash units also include smart sensors to measure ambient light, distance and other optical parameters in order to make the most of the flash effect.
Digital cameras can use their flash units in automatic or in manual mode. In automatic mode the camera measures ambient light and fires the flash when not enough ambient light is available. Sometimes the camera will make the wrong decision as to using the flash and will either fire or not fire the flash when the opposite was needed. Setting the flash intensity is important too. If the flash unit fires too much light energy on objects that are too close to the camera the digital photo will be washed out. On the other hand if the flash unit fires a small amount of light energy on an object that is farther away from the digital camera the digital photo will be a too dark.
Flash units have limitations too. They can not light any scene and any object at any distance from the camera. It is important to know your flash unit limitations. For example check what the maximum light energy that it can emit is and what the farthest that an object can be effectively lit from. This is also known as the effective flash range. If the object is out of the effective flash range it is actually better to turn off the flash altogether and use a tripod with a longer exposure. Sometimes it is useful to use the flash even if there is enough ambient light. In such cases you can manually force the camera to fire the flash. This is also known as fill-in flash as it is usually used to fill-in shadowed areas on objects in the digital photo.
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