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 2-6-0 at Brighton, Derby and Doncaster. Although the boiler shared flanged plates with the GWR No.2 boiler the barrel was shortened by inches and a dome added. Strangely the class did not share the same design of wheels as the Doncaster-designed BR Standard Class 4 2-6-0 (76XXX), which also had driving wheels and the same piston stroke, and hence crank-pin throw. In common with a number of the other BR Standard Classes, the chassis design used a number of LMS-designed components including Brake Hanger Brackets, Flexible Stretcher Brackets and Reversing Shaft Brackets. The cylinder covers of engines as built were fitted