The Canon Camera Guide to Flash Terminology.
This flash terminology guide will give a brief overview of the various terms and idea used commonly with respect to the Canon EOS flash photography.
Flash units and Strobe
What is the main difference between a Flash and strobe is just whether you are using UK or US English. We refer a strobe as a flash unit in the US whereas the British uses the word as meaning anything which emit blinking lights. Other commonly used terms which cause confusion in flash photography are the words “Speedlight” and “Speedlite”. Speedlight is actually the brand name of Nikon series of flash units while Speedlite is the brand name of Canon series of flash units.
Guide Number
The maximum distance which a flash unit can reach with its flash pulse is known as the guide number. But if you are using automatic flash metering, this number is not important at all. You will only need to know this number when you are more inclined to do manual settings for your flash.
Exposure value (EV)
Used for determining the sensitivity of the Auto Focus or (AF) system or exposure metering for film types or a lens, the EV or Exposure Value is a combination of both Aperture settings and Shutter speed. The numbers 1/125 and F2 give an EV value of 9 which can also be obtained from F4 and 1/30.
Non Dedicated and Dedicated Flash Units
Dedicated flash units are flash units designed by the Camera manufacturers for their own range of cameras. These flash units can communicate with the camera system allowing for more precision photography. For example Canon manufactured the “speedlite” range of flash units for their EOS cameras. Non dedicated flash units are those flash units usually manufactured by third party manufactures. They normally work the same way on all brands of camera with little or no communications with the camera unit itself.
Shoe Mount
Usually located on the top mirror or prism housing, the shoe mount is a slide-in rectangular socket meant for attaching an external flash unit to the camera. They are also known as “Hot Shoe Mount” as they possess an electrical circuit which will initiate the flash unit once it is attached to the camera. Canon EOS cameras have an additional four electrical points in the shoe mount which transmit data from the flash trigger.
Redeye Effect
When the light from a flash unit is reflected back into the camera off the walls of the retina, this will produce the Redeye effect which we always see in pictures taken in low ambient light conditions. This due to the fact that the low ambient light condition causes the pupils of the eyes to dilate bigger and the color red is because the retina walls are lined with red blood vessels.
Redeye Reduction
To circumvent around the problem of redeye effect, there are several ways to go about this. One effective way is to move the flash away from the lens or reflect the flash light off the walls onto the subject instead of directly illuminating the subject. Another way is to get the subject to view a bright light just before taking the picture of the subject. This causes the pupils of the eyes to dilate smaller and therefore decreasing the reflective effect of the retina.
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