Camera FlashPhotography is often described as "painting with light". A camera is simply a machine that captures and records light. It is the photographer - as an artist - -who controls the way the machine captures the light - how much, from what angle, for how long and so forth. All of these variables affect the exposure and ultimately the final image itself. But sometimes things don't work out. Sometimes the light doesn't want to cooperate with the needs of the photographer and it is at these moments, when all else fails, that we turn to the flash.
How does a flash works?There are two answers to the question of how a flash works. The short answer is that a flash is bright light which bathes the subject of a photograph with an even tone of light to enhance the natural or ambient lighting. This will help in reducing blur and bringing out darker areas.The longer answer is that a flash works by storing charge in a battery and then transferring it to a powerful capacitor. This capacitor being charged is indicated on the camera in a variety of different manners depending on brand. When the shutter button of the camera is triggered the charge from the capacitor is released into a tube of xenon gas, exciting the particles and creating an extremely bright, white light. This is very similar to how fluorescent or neon lights work. The primary difference is the gas used (xenon) and the length of time which the charge is maintained (very, very briefly). The flash is timed - this is called flash synchronization - to the shutter in such a way that the reflected light from the flash is evenly distributed over the photo sensitive substrate (film or sensor). The light from a flash will illuminate less at increasing distances due to something called the inverse square law. Because the light is diffusing from the flash bulb it gets less intense the farther it travels from the bulb. The amount of light drops off in such a way that if you doubled the distance to an object only 1/4 of the light would reach it. Because of this flashes have limitations. A subject shot with a dark, distant background using a flash may appear to be standing in front of nothing but darkness. This is because the things in the distance were far enough away that light from the flash didn't reflect strongly enough to be picked up.
What kinds of flash are there?
Internal flashes are very common in small, portable handheld cameras. These cameras often have a small sensor and a small, slow lens and the flash is a great aid to these cameras. Use of a flash can increase the amount of light available for a sensor to process resulting in a sharper, more distinct image. Unfortunately, due to the proximity of the flash to the lens these types of flash setups can have some unwanted side effects, as we shall see.
Another type of external flash is the Master/Slave system. This system uses a variety of flashes to light the subject from multiple angles. The primary flash which is set off with the shutter is called the master flash. The slave flashes are placed wherever they are needed and these flashes are set to react to the light of a flash. Seems redundant right? When the light of the master flash hits one of the slave flashes it activates it. There are other master/slave systems where the flashes are hard wired together and the timing is controlled through the wire.
When should I use a flash?There is no simple way to answer this question. A flash can be used in almost any situation or avoided in almost any situation. Flash photography can have a very characteristic feel to it and it is up to you, the painter of light, to decide if that feel is right for you and right for the photograph you are trying to capture. Flashes can have such a wide range of effects that rather than trying to present a set and clear rule for when and how to use flashes I will try to present some of the various ways flash can affect your image.
The GoodFill Flash - fill flash is potentially the best and most useful way to use a camera flash. Using the flash to supplement the natural light rather than overpower it fill flash lets you create beautifully exposed images even with extremely challenging lighting conditions. The most common use of fill flash is illuminating a backlit subject. Suppose you are with your friend watching a beautiful sunset. The light is still bright enough that your camera doesn't automatically engage its flash. This is great for the sky but when you try and snap a picture of your friend against the bright sky they are too dark to see. If you turn on your flash - possibly by overriding the automatic setting - you may be surprised to find that you can take a picture where the sky is still vivid but your friend is also well defined and correctly exposed.Low lighting - flashes will help you to take clear, pictures even under low lighting conditions. Because flash intensity follows the inverse square law you need to be relatively close to your subject. Within the appropriate range flash will illuminate with even white light and bring out details that would otherwise be lost to the darkness. As you may expect more powerful flashes have a more powerful range and this range is indicated by the guide number of the flash. Avoid blur - because flash quickly and brightly illuminates the subject of the photograph pictures taken with flash tend to avoid blur. A fast flash and a fast shutter is capable of clearly capturing extremely fast rapid motion. Experiment with your camera settings to see what is possible!
The BadHarsh light - one of the drawbacks to flash photography is the quality of the light created by a xenon lamp. This cold, white light can bring out the worst in certain subjects especially making peoples faces look washed out. A related problem is the bright glare of the flash off of any reflective objects within the frame. These types of problems can be eased by using a diffuser or reflecting the flash off of a nearby object to avoid direct glare.Flat tone - another challenge is avoiding a flat tone. Many built in camera flashes will illuminate the subject from almost exactly the same angle as the shutter views it, the result is that - much like the sun overhead at high noon - shadows tend to disappear underneath objects and a flat tone can develop. Reflecting off the ceiling or a wall will help with these types of problem. Also try using a slower shutter speed - may require a tripod - to capture more of the natural light and shadow. Loss of natural lighting - related to the above to problems is the loss of natural lighting. Natural light - especially at dawn or dusk - can have a beautiful tone to it which many photographers strive to capture. A flash can ruin this light by washing out warm natural tones with a flat, white glow. Creative solutions - such as backlighting the subject and using fill flash - can work around this but capturing natural light remains one of the greatest photographic challenges.
The UglyRed Eye - one of the most unfortunate side effects of using a photographic flash is the dreaded red eye. Red eye strikes when the subject looks directly at the lens when the lens and the flash are in line. Light from the flash reflects off the back of the eye and onto the camera sensor. Blood in our eyes causes the red tone. Red eye can be avoided by using an external flash. You can also have subjects look slightly away from the camera. If red eye can't be avoided you can always try and remove this effect with one of a number of different programs.Black shadow - another ugly visual drawback of using a flash happens when the subject is close to a wall or other surface. The bright flash creates a hard, black shadow on the wall which is very distracting photographically. This shadow may be avoided by angling the flash so it reflects off another wall - maybe even behind you - or simply not using a flash when the subject is very close to a wall.
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