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
BR Standard Class 2 2-6-0 BR Standard Class 2 2-6-0 The BR Standard Class 2 2-6-0 is a class of steam locomotive, one of the British Railways Standard classes of the 1950s. They were physically the smallest of the Standard classes; 65 were built. The design was derived from the Ivatt-designed LMS Class 2MT 2-6-0, with a reduced cab to enable it to fit into a universal loading gauge, and other standard fittings, most notably a taller chimney, others including the lack of an Ivatt dome and side plates connecting the two sections of the engine. Like the LMS predecessor the BR design had a