Affordable Photography

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 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)

EV or Exposure value is the value used for deciding the sensitivity of the AF (Auto Focus) system or exposure metering which respect to film types or lenses. You need to combine the aperture and shutter speed together to get this value. For example, 1/125 and F2 is equal to EV9 which is also equivalent to F4 and 1/30.

Non Dedicated and 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 rectangular slide-in socket which is usually located on top of the mirror or prism housing is known as the shoe mount. This mount is usually used for affixing the external flash unit to the camera. Sometimes it is called a Hot Shoe Mount as it has an electrical trigger to initiate the flash unit once the external flash is fixed to the camera. The Canon EOS Cameras have 4 additional contact points in the shoe mount which helps to transmit flash data from the 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 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.