When Harold Edgerton invented the modern electronic flash in 1931, the world of photography was revolutionized. The principle behind the electronic flash is that when you charged up a capacitor or condenser and release the energy through a flash light bulb (A glass bulb containing inert gases), a split second burst of light will occur. This output of light occurs instantly when you send power to the flash light bulb. Therefore you can control this output of light through regulating the duration of electrical pulses to be sent to the flash light bulb. Before the advert of modern electronics, the duration of electrical pulses used to be controlled by a component called the thvristor. Today, modern electrical circuitry has taken over the function of this component.
In normal photography, there are two ways to control the amount of light entering camera. One way is by adjusting the shutter speed which affects HOW LONG the exposure time will be. The other way is by adjusting the aperture of the lens. This will affect HOW MUCH light will enter the camera. You can also use filter to block out additional light but in this guide we will only discuss about the basic ways how flash exposure can be controlled. Flash photography differs from normal photography because flash timing involves split second of light. As such, the shutter speed does not play any role in determining the amount of light entering a camera except when the camera is in FP mode.
The Camera's shutter speed is only relevant when the ambient light is continuous source. Due to the fact that the flash pulse time span is so brief, the mechanical shutter have no time to even register any changes in the light source. Thus in order to control the amount of light which enter the camera, you have to:
Change the physical diaphragm of the camera lens which is the lens aperture. Doing so allows you to control the amount of light that can enter the camera.
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.
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.
Lastly, we can affect the duration of the flash burst by adjusting the duration of the electrical pulse to the flash unit therefore controlling the amount of light produced. This is the primary ways today how we control 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. - 16752
In normal photography, there are two ways to control the amount of light entering camera. One way is by adjusting the shutter speed which affects HOW LONG the exposure time will be. The other way is by adjusting the aperture of the lens. This will affect HOW MUCH light will enter the camera. You can also use filter to block out additional light but in this guide we will only discuss about the basic ways how flash exposure can be controlled. Flash photography differs from normal photography because flash timing involves split second of light. As such, the shutter speed does not play any role in determining the amount of light entering a camera except when the camera is in FP mode.
The Camera's shutter speed is only relevant when the ambient light is continuous source. Due to the fact that the flash pulse time span is so brief, the mechanical shutter have no time to even register any changes in the light source. Thus in order to control the amount of light which enter the camera, you have to:
Change the physical diaphragm of the camera lens which is the lens aperture. Doing so allows you to control the amount of light that can enter the camera.
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.
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.
Lastly, we can affect the duration of the flash burst by adjusting the duration of the electrical pulse to the flash unit therefore controlling the amount of light produced. This is the primary ways today how we control 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. - 16752
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
