The Canon Camera Flash Terminology Guide
This general guide will help to explain to you some of the concepts and terms used in relation to Canon EOS flash photography.
Flash 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 guide number is the maximum range of a flash unit when it gives out its flash pulse at its maximum setting. However, if you are using automatic flash metering, the number is not relevant. This number only becomes important when you are involved in manual flash settings.
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.
Dedicated or Non dedicated flash units
Camera Manufacturers like Canon manufacture their own line of flash units to cater for their own range of cameras. The Canon line of flash units is known as the Speedlite series. These flash units are able to communicate with camera system thus allowing the photographers to enjoy more precision photography. They are called dedicated flash units. Non dedicated flash units are those flash units which are manufactured by third party manufacturers. They are usually generic and are not able to communicate with the camera system.
Shoe Mount
The shoe mount is a slide in socket rectangular in shape located on the top mirror/prism housing. This socket is used for affixing the external flash unit to the camera. They are also called “Hot Shoe Mount” as they have an electrical trigger which activates the flash unit. The Canon EOS cameras have additional four electrical contacts within the shoe mount which carries signal data apart from the main flash trigger.
The Redeye Effect
The redeye effect is a common problem in flash photography. This is a result of flash light which is reflected back into the camera after it bounces off the retinas of the eyes which is lined with red blood vessels. Usually it occurs when the low ambient light cause the pupils of the eyes to dilate bigger to let more light enter the eyes.
Redeye Reduction
To reduce the problem of Red Eye, one can use several methods. The most effective way is to distance the flash away from the lens or bounce the flash light onto the subject as opposed to flashing directly at the subject. The other way is for the subject to observe a bright light source just before taking the subject picture. This will make the pupils smaller and thus lessening the reflective capability of the retina.