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.
Generally, there are two ways to control the quantity of light that enter the camera. The first way is adjusting the speed of the shutter which will affect how long the exposure time will be. The second way is through adjusting the aperture of the lens. This will determine how much light will enter the camera. Although you can use filter to block out additional light but here we will only talk about the fundamental ways of how to control flash exposure. Flash photography is an entirely different ball game because the flash pulse involves only micro seconds' display of light. As such, the mechanical shutter speed does not play any part in determining the amount of light which enter the camera except when the camera is in FP mode.
The shutter speed of a camera will only be effective if the light from the environment is a continuous source. However, flash light burst is so brief that the camera shutter hardly has time to register the change in the amount of light. As such to control the amount of light of a flash unit entering the camera;
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.
One can by adjusting the physical distance between the flash unit and the subject matter, control the amount of light going into the camera. Light follows the laws of physics, so the further the distance one is from the light source, the lesser is the amount of light available.
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.
Finally, by regulating the duration of the electrical pulse to the flash unit, you can control the duration of a flash burst. Therefore you will change the final flash output by such control. In fact, this is the primary way nowadays people use to control the electronic flash.
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. - 15437
Generally, there are two ways to control the quantity of light that enter the camera. The first way is adjusting the speed of the shutter which will affect how long the exposure time will be. The second way is through adjusting the aperture of the lens. This will determine how much light will enter the camera. Although you can use filter to block out additional light but here we will only talk about the fundamental ways of how to control flash exposure. Flash photography is an entirely different ball game because the flash pulse involves only micro seconds' display of light. As such, the mechanical shutter speed does not play any part in determining the amount of light which enter the camera except when the camera is in FP mode.
The shutter speed of a camera will only be effective if the light from the environment is a continuous source. However, flash light burst is so brief that the camera shutter hardly has time to register the change in the amount of light. As such to control the amount of light of a flash unit entering the camera;
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.
One can by adjusting the physical distance between the flash unit and the subject matter, control the amount of light going into the camera. Light follows the laws of physics, so the further the distance one is from the light source, the lesser is the amount of light available.
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.
Finally, by regulating the duration of the electrical pulse to the flash unit, you can control the duration of a flash burst. Therefore you will change the final flash output by such control. In fact, this is the primary way nowadays people use to control the electronic flash.
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. - 15437
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
