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 Music Number International Standard Music Number The International Standard Music Number or ISMN (ISO 10957) is a thirteen-character alphanumeric identifier for printed music developed by ISO. The original proposal for an ISMN was made by the UK Branch of IAML (International Association of Music Libraries, Archives and Documentation Centres), put forward by Alan Pope (Blackwell's Music Department, Oxford), Malcolm Lewis (music librarian in Nottingham) and Malcolm Jones (music librarian in Birmingham). A draft ISMN structure and application was presented at the 1987 IAML conference in Amsterdam, then after further discussions at the 1989 IAML conference in Oxford it was decided that the