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 4 2-6-0 locomotive. In time, the moulding tools passed on to Dapol who have also produced the model kit. Bachmann produces a ready-to-run model in both 00 and N gauge. BR Standard Class 4 2-6-0 The BR Standard Class 4 2-6-0 is a class of steam locomotive designed by Robert Riddles for British Railways (BR). 115 locomotives were built to this standard. The class was designed at the ex-LNER works at Doncaster which was also responsible for building 25 of the 115-strong class. The remaining 90 were split between Horwich and Derby Works. The last in the series, No.76114, was also the