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 3 2-6-2T was transferred away. During this repaint, it mistakenly received a power classification 4 numeral which it carried until withdrawal. Tri-ang produced an OO Gauge model of the locomotive in BR Green and BR Black although this was by modern standard under-detailed being produced in the 1960s, but Bachmann announced a brand new OO gauge model in February 2009. An N gauge version has also been released by Bachmann under their Graham Farish brand. BR Standard Class 3 2-6-2T The BR Standard Class 3 2-6-2T was a class of steam locomotive designed by Robert Riddles for British Railways. It was essentially