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 at the Severn Valley Railway, are now in an advanced state. Further parts and patterns continue to be amassed with wheels and axle-boxes cast and cylinders on order. With construction work on the new engine advancing every week the Trust classifies 82045 as the 1001st steam locomotive to a BR Standard design since the commencement of its construction follows that of 72010 "Hengist". Unlike a number of other "new-build" projects the group building 82045 will equip the locomotive with a traditional riveted boiler complete with copper firebox. The 16-spoke driving wheels from BR standard class 4 2-6-0 No.76080 – which