The modern Electronic flash was invented by Harold Edgerton in 1931. Its introduction into the modern photographic world changed the photography as we know it today. The theory behind flash photography is that when you take a capacitor or condenser, charge it up and then release the electrical energy through a glass bulb filled with inert gases (Flash Light Bulb), you will get a split second burst of bright light. This emission of light occurs immediately after you send a pulse of electrical energy to the flash bulb. As such, there is a mean of control of the light output by way of controlling the electrical pulse duration to be sent to the bulb. Previously, a component called the thvristor was used to control this duration of electrical pulse. Nowadays, this process is automated with the use of 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 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;
You can change the size of the aperture of the lens. This is the physical diaphragm of the lens which controls the amount of light entering the lens.
Adjust the distance between the subject and flash unit. This method is an application of the laws of physics. The further an object is from a light source, the less illuminated the object is.
One can also control how much light there is between the flash unit and the subject matter by using diffuser. Although this is a possible way, one also has to consider the inconveniences of carrying all these items around 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 conclusion, this is the main principle of flash metering. The precise measure of flash metering is difficult and it requires years of experience before anyone can accurately judge the right duration for the electrical pulse to be sent to the flash unit. Nowadays, we are fortunate as camera like the Canon EOS digital camera fulfill this function automatically with modern 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 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;
You can change the size of the aperture of the lens. This is the physical diaphragm of the lens which controls the amount of light entering the lens.
Adjust the distance between the subject and flash unit. This method is an application of the laws of physics. The further an object is from a light source, the less illuminated the object is.
One can also control how much light there is between the flash unit and the subject matter by using diffuser. Although this is a possible way, one also has to consider the inconveniences of carrying all these items around 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 conclusion, this is the main principle of flash metering. The precise measure of flash metering is difficult and it requires years of experience before anyone can accurately judge the right duration for the electrical pulse to be sent to the flash unit. Nowadays, we are fortunate as camera like the Canon EOS digital camera fulfill this function automatically with modern electronics.
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
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