Since the invention by Harold Edgerton in 1931 of the modern electronic flash, Photography has never been the same. The principle of electronic flash works by charging up a condenser or capacitor then releasing the charge in a split second burst of light from a flash light (a glass bulb filled with inert gases). The output of the flash light response instantly to the presence of power which is being sent to the flash light. As such the main form of control over the output of the light output is dependent upon the duration of electrical pulse sent to the bulb. It used to be that the electrical pulses was controlled by a component called the thyristor however today, modern flash units are completely automated by electronics.
On the whole there are two ways to control the amount of light which enter the camera. By adjusting the shutter speed you can determine how long the exposure time is. The other way is to adjust the aperture of the lens. By doing so you will how much light will get to enter the camera. However Flash photography is different from normal photography. This is because of the speed of a burst of the flash light. The time taken for a burst of light takes only micro seconds. This time frame is so short that the speed of a mechanical shutter is no longer a relevant factor in determining the amount of light entering a camera except when the camera is programmed under the FP mode.
The speed of the camera's shutter is only important when the ambient light is a continuous source. But the duration of a flash pulse is too brief for the camera mechanical shutter to even react to the change of light. Therefore the way to control the quantity of a flash pulse entering the camera is by:
Changing the lens aperture size. The aperture is the physical diaphragm of the camera lens and this control the quantity of light which enters the lens.
You can also adjust the physical distance from the flash unit to the subject. This will also control the quantity of light going into the camera. The laws of physics dictates that the further the distance between the light source and an object, the lesser the amount of light hitting the object.
You can also regulate the amount of light from a flash unit to a subject by using a diffuser. Of course, you have to consider the trouble of lugging around all these items on location.
By regulating the duration of electrical energy to be sent to the flash unit. By control the energy pulse, you control the duration of the flash burst. This allows you to determine how much light will be emitted to enter the camera. Nowadays, this is the principal way to control the electronic flash output.
In essence this is what flash metering is all about. Precise adjustment is not easy and usually takes years of experiences before one can correctly determine the amount or duration of the electrical pulse to set the flash unit too. Fortunately modern Camera like the Canon EOS digital camera has automate the system making it a breeze even for the novice to set the duration of the flash burst to take the ideal picture. - 16747
On the whole there are two ways to control the amount of light which enter the camera. By adjusting the shutter speed you can determine how long the exposure time is. The other way is to adjust the aperture of the lens. By doing so you will how much light will get to enter the camera. However Flash photography is different from normal photography. This is because of the speed of a burst of the flash light. The time taken for a burst of light takes only micro seconds. This time frame is so short that the speed of a mechanical shutter is no longer a relevant factor in determining the amount of light entering a camera except when the camera is programmed under the FP mode.
The speed of the camera's shutter is only important when the ambient light is a continuous source. But the duration of a flash pulse is too brief for the camera mechanical shutter to even react to the change of light. Therefore the way to control the quantity of a flash pulse entering the camera is by:
Changing the lens aperture size. The aperture is the physical diaphragm of the camera lens and this control the quantity of light which enters the lens.
You can also adjust the physical distance from the flash unit to the subject. This will also control the quantity of light going into the camera. The laws of physics dictates that the further the distance between the light source and an object, the lesser the amount of light hitting the object.
You can also regulate the amount of light from a flash unit to a subject by using a diffuser. Of course, you have to consider the trouble of lugging around all these items on location.
By regulating the duration of electrical energy to be sent to the flash unit. By control the energy pulse, you control the duration of the flash burst. This allows you to determine how much light will be emitted to enter the camera. Nowadays, this is the principal way to control the electronic flash output.
In essence this is what flash metering is all about. Precise adjustment is not easy and usually takes years of experiences before one can correctly determine the amount or duration of the electrical pulse to set the flash unit too. Fortunately modern Camera like the Canon EOS digital camera has automate the system making it a breeze even for the novice to set the duration of the flash burst to take the ideal picture. - 16747
About the Author:
Tim Harris is a canon camera enthusiast. For tips on choosing and buying cameras, do check out Canon OS Camera website. Camera 40D Digital Rebel XTI 3D Blog
