Update : Sunday, January 15, 2012
Flash is used to change the lighting of a scene. We also use it when taking pictures where quick movements are present.
The current flashes are more devices 'TTL'. Which means they can translate the information from the camera to meter power correctly when taking the picture. This will avoid to have an image burned by the flash or not enlightened enough.
Use in daylight as a surprise to most people. However this use will help correct some areas become too dark compared to the rest of the image. Such use is called 'Fill-In '.
The power of a flash is characterized by its 'Guide Number', which means the distance at which you can shoot with the flash correctly. Guide This number is provided by default with an aperture of f/1 ISO 100.
You can calculate the aperture for taking correct and consistent image. It is reflected in the nominal guide number of the flash divided by the distance in meters of the subject.
You have a flash with a guide number of 56 and your subject is 12.6 meters, it will give you an aperture of f/4.4. So, you can use a maximum aperture of f/4.4. computes This takes into account the fact that you would with a sensitivity of ISO 100.
In case, you would use a different speed. You would calculate the new Guide Number of your flash.'s Formula is the square root of ISO used and divided by 100 ISO, which will increase to Flash Guide Number.
Having changed the sensitivity of your camera to ISO 400 and you have a flash with a Guide Number of 56. You could actually flash with a Guide Number of 79 equivalent.
We can distinguish several types of Flash.
4.4 = 56 / 12.6
New Guide Number = (v (ISO Utilisé/100 ISO)) * Number of Real Guide
79.1959 = (v (400/100)) * 56
Flash Case
The flash of the case is the easiest to use and easier. This is not the most convenient flash, less powerful and not removable. Moreover, they take a lot of the energy housing. However, being integrated within the camera, transport is facilitated.
Some devices do not have built-in Flash. These are the most professional equipment.
Cobra Flash
This flash is probably the best known. It takes its name from when the animal stands on its tail close to attack.
Most people avoid using this type of flash because it causes congestion. They exist in several sizes and weights, which are obviously related to their powers. They are fully programmable much in the power of flash in the number of flash (one by one, or burst).
In recent years new Flashes cobra appeared, with the particularity to move their heads on the two planes, vertical and horizontal.
Ring Flash
This is the specialist in macro photography. Built with Flash or Cobra, you have a lot of problems in order to have a beam of light is not blocked between the flash and the subject. So you end up with one shadow cone in front of the lens.
This equipment is positioned directly on the edge of the lens which results in a beam without hindrance.
Flash Studio
This tells Flash electronics equipment, has in general a halogen bulb. Increasingly Flash Studio is equipped with LED flash. Assistant There umbrellas, screens, or cones to disseminate light premise in the direction of the subject and to manage the beam, so the amount of light that we have decided to target.
Its activation is effected either by cable or by infrared. When using the infrared mode, the case emits a pulse which triggers the flash via photoelectric cells.
Photo taken with a Canon 5D Mk II and a Canon 70-200mm (ISO800 - f/5.6 - 1/200s)