Gerd Ludwig, a National Geographic veteran known for his powerful photo essays, is one of the leading documentary photographers of our time. In Minus 2/3—The Invisible Flash: Crafting Light for Photographers in Field, Ludwig takes us behind the scenes of many of his most iconic images to share his approach to lighting with small flash.As a photographer focusing on diverse cultural and environmental stories, Ludwig is often confronted with a wide r...

The analysis of ejaculate, known as the spermiogram, is the crucial investigative technique in the andrological check-up for childlessness. Althoug other impor tant factors such as medical history, physical examination, hormone analysis and tests, biochemical, microbiological, immunological, and genetic tests, and histological and histochemical investigations must all be considered before a final assessment can be made of male fertility, the spermiogram is the guiding factor in estimating ...