If you are thinking of buying a flash unit you will be well advised to consider the Metz range of models. A wide range of models ensures that there is the right one for every need to support even the most creative ambitions. In spite of a very sophisticated technology, Metz mecablitz units are robust to stand up to any photographic situation, and they are extremely simple to operate. The Metz range embraces models with guide numbers between 15 and 76. Such an enormous light output makes the mecablitz the ideal complementary companion of the sun.
Guide Numberl = aperture x distance
The guide number specifies the maximum light output of the given flash unit. This output is always based on a content_text film speed of ISO 100/21°. The type designation of Metz mecablitz flash units indicates their capacity. For instance, 50 AF means that the flash unit has a guide number of 50. The guide number is calculated on the bases of the aperture and the flash-to-subject distance:
With the above formula you can calculate that with a guide number of 50 and an aperture of f/4, a subject can be shot at a maximum distance of 12,5 meters. (guide number 50 = aperture 4 x distance 12,5 m)
Almost all Metz mecablitz flash units feature an aperture calculator to eliminate tedious mental arithmetic. Once the film speed has been set the appropriate f-stop will be indicated for any flash-to-subject distance and the photographer can fully concentrate on the subject.