Archived posting to the Leica Users Group, 1997/12/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Second message to infinity computations. Assume we take 'infinity' as the distance at 1000 meters. Then with a 50mm lens the reproduction factor is about 1:20000 and with a 21 mm 1:47619. If we next assume that the maximum usable resolution is 40lp/mm (cycles/mm) or .0125mm, then two image details next to each other to be resolvable with a 21mm needs to be at a distance of 595mm. In it self incredibly close. For a 50mm this distance is 250mm. But now: stay with the minimal distance for the 21mm (595mm) and take these objects with a 50mm--->we still have 595mm, but now the 50mm needs only ~20 cycles/mm to record the distance. And if you take a look at the MTF figures of modern lenses and you will see that at 20cycles/mm the performance is vastly better than at 40cycles. It is quite natural that at the same far distance the performance of the 50mm must be better than with any 35 or 28 or 24 or 21. To be fair you can only compare the infinity performance of lenses with the same focal length. Erwin