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 6 72010 Hengist the same year when 72008 Clan MacLeod was scrapped. Since no original engines were saved "The Clan Project" plan to build one of the unbuilt engines which would have been allocated to the southern region had it been constructed. The engine will be built to modern mainline standards and being a go anywhere engine aswell as being a low maintenance design will also be ideal for use on heritage railways aswell as hauling railtours. 999 BR standards were built and 72010 will be the 1000th BR Standard engine to be built when completed BR Standard Class 6 72010 Hengist No.72010