Understanding Digital Camera Flash Units

By Dan Feildman

Flash units can come in many sizes and shapes for digital photography. Those cameras on the lower end of the scale come with low energy built in flash units. However, some gear such as the high end digital SLR cameras can accommodate external flash units advanced in their abilities to provide excellent lighting in complicated situations. Know the basic facts about the difference between built in and external flash units.

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.

Today flash units have eliminated this challenge. An electronic flash tube ensures flash timing is synchronized to the camera. The photographer now gets to concentrate on other aspects of the photo. New digital cameras can even determine on their own if the flash is even needed, set its intensity and other parameters and fire the flash at the precise time the shutter is opened. All of this is automatically done in the background. Should the user want to make their own adjustments, digital cameras also allow the user to manually control the flash, set its intensity and more.

Flash units are divided into two categories: Internal built-in flash units or external flash units. Internal flash units are built into the camera. Almost all digital cameras include such a unit and allow 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 support external flash units. Usually the lower end pocket cameras do not allow external flash units while all high end digital SLR cameras do allow such external flash units. External flash units can vary a lot. 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 optimize the flash effect.

Both automatic and manual flash unit modes are made available on digital cameras. In automatic mode the camera measures ambient light and fires the flash it deems not enough ambient light is present. There can be times the camera will make a mistake in using the flash and will either fire or not fire the flash when the opposite was needed. Keep in mind the importance of setting the flash intensity. Should the flash unit fire too much light energy on objects that are too close to the camera the digital photo will be washed out. 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 then 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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