Choice of the Digital Camera Aperture

Automatic flashes usually offer the possibility of working with two or more different apertures. While with the manual flash the aperture is set by the distance, in automatic we select an aperture value that remains constant. In the choice of the aperture many things are going to influence our decision: in first place, the depth of field we need (taking in account that in situations of scarce lighting precise focus is very difficult and some depth of field will avoid unwanted lack of focus); in second place, the action radius we need to cover; in third place, the presence of other light sources in the image (9.5); an, finally, the need of economizing the available energy, specially when it is scarce.

The action radius we dispose of is smaller the smaller the aperture, and is given with the expression NG/f. For example, if the guide number of a flash is 32 and the system offers the possibility of working in automatic with f4 or f8, the limit distance for the first aperture is 8 m, and of 4 m for the second. The consumption of energy and, therefore, the duration of the recharge cycle of the devise will be smaller the greater the aperture. From the apertures the system lets us choose from, the largest one means minimal depth of field, greater registration of other light sources, maximum action radius and minimal energy consumption. When we select the smallest aperture that the system offers, we are on the other extreme.