H Number

H Number

H Number, also known as Hurter and Driffield number, is a term used in photography to describe the sensitivity of photographic materials. It is a numerical value that indicates the amount of light required to produce a given density on a photographic negative or positive. The H Number is determined by measuring the logarithmic density differences in a photographic negative, which helps to determine the blackest point in a black and white print. The H Number is an important concept in photographic developing, as it helps to determine the optimal exposure time and developing conditions for a given photographic material. By measuring the H Number, photographers can ensure that their images are properly exposed and developed, resulting in high-quality prints with accurate tonal values and contrast. The concept of the H Number was first introduced by Ferdinand Hurter and Vero Charles Driffield in the late 19th century, and it has since become an important tool in the field of photography. The H Number is used to measure the sensitivity of photographic materials, including film and paper, and it is an essential part of the sensitometry system developed by Hurter and Driffield. Overall, the H Number is a crucial concept in photography, as it helps to ensure that images are properly exposed and developed. By understanding the H Number and its significance, photographers can create high-quality prints with accurate tonal values and contrast.

H Number, Hurter and Driffield, sensitivity, photographic materials, exposure time

— Andrew Moore