F-number lengths. Therefore, reduced–depth-of-field effects will require smaller f-numbers when using small-format cameras than when using larger-format cameras. Image sharpness is related to f/number through two different optical effects: aberration, due to imperfect lens design, and diffraction which is due to the wave nature of light. The blur optimal f-stop varies with the lens design. For modern standard lenses having 6 or 7 elements, the sharpest image is often obtained around 5.6–8, while for older standard lenses having only 4 elements (Tessar formula) stopping to 11 will give the sharpest image. The larger number of elements in modern lenses allow the
International Standard Authority Data Number of an ISADN continues to be relevant to the information science community, as it could be a great help in the problem of measuring an individual author's research output. International Standard Authority Data Number The International Standard Authority Data Number (ISADN) was a registry proposed by the International Federation of Library Associations and Institutions (IFLA) to provide and maintain unique identifiers for entities described in authority data. Having such a unique number would have the benefits of being language-independent and system-independent. Francoise Bourdon was a major proponent of such a standard, proposing a structure for the ISADN and recommending that