Digital Camera Flash

The digital camera flash is an intense and portable light source, of necessary use in insufficiently lightened interiors, nighttime, etc. This broadening of our field of action can nonetheless be frustrated by quality and technical problems that this mysterious illumination apparatus can cause.

The largest inconvenience of using a flash with film is it's instantaneousness. During the flash we can have a clear idea of the illumination and it's quality, or the effective exposure level. Exposure errors, if are not adverted in the moment of the shot, can spoil entire rolls of film. One of the large advantages of digital cameras is that they allow us to immediately see the quality of the image obtained when using flash. The direct flash is a hard and flat light source, not appreciated. We are going to get to know this accessory a bit better and try to solve some of the mentioned inconveniences.

The first "models" of flash caused an instant combustion of magnesium dust. Further on, it was limited to the burning of a crystal bulb, and explosive material was used on the filament for it's rapid combustion. This way lamp flashes appeared, very effective, which required a change of bulb with every shot. Lamp flashes disappeared with the electronic flash. The only remembrance of this type of flash is in older shutter models, that include a synchronization option characteristic of lamps.

In electronic flash, the light is generated through an electric discharge of a high voltage, which passes through the gasses contained in the tube or lamp of the devise. Through an action of the electricity, these gasses, appropriately chosen for color temperature effects, emit a very intense and very short flash; once charged, it's ready for a new shot.

The Manual Flash

We have seen in 6.1.1 that the intensity of incident light on a point depends on the distance there is from the point to the source of light: the intensity is inversely proportional to the square of the distance. When we double, triple or quadruple the distance from the point to the light source, the intensity of the incident light on the point will respectively be four, nine or sixteen times smaller. Let's now examine a flash in "manual" functioning mode, were it emits a flash of a fixed intensity. The intensity of incident light on the objects it illuminates will be smaller, the greater the distance it is from it. To maintain a constant exposure level when varying the distance, we have to adapt the illumination's variable intensity through the diaphragm's aperture. When the object is close to the flash we need a more closed aperture than when the object is far.

Lets suppose that the manufacturer of the flash tells us that, in manual mode, the diaphragm's aperture that is necessary to correctly expose an ISO 100 film when photographing an object placed at a meter away is, for example, f16. From this we can deduce the corresponding apertures for other distances, because if we double the distance (2 m) the intensity is reduced in four, and we will have to compensate by opening the diaphragm's aperture two steps (f8). If the object is a four meters, the intensity will be sixteen times less than a meter, and therefore the correct exposure will be achieved by opening the diaphragm four steps (f4). If the object is placed at half a meter, we will have to close the diaphragm two steps (f32) because the intensity is now four times greater than at a meter.