Archived posting to the Leica Users Group, 2006/02/10
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Eric wrote: > Jonathan: > >> In digital one can likewise underexpose until the image becomes >> background noise. 5 stops up from this gives an "ISO" for which a >> Zone 0 is background noise (pure black in the digital world). > > That's making the assumption that digital has exactly 10 stops from > pure > black to pure white. I'd say that assuming digital will behave > exactly like > a negative is a faulty assumption, and comparing results from Canon > vs. > Leica based on that is going to be a meaningless comparison. No assumptions. This test is designed to hold shadow detail constant while measuring the effective speed of a sensor e.g. the DMR vs Canon. I am not suggesting that working photographers need to do this -- unless they are curious about which sensor to purchase and want a semi numerical way to compare different sensors. You need to understand how a digital sensor works in order to really understand why this might be useful, but just consider this akin to the "Zone System" which itself was designed to tailor different film emulsions (each having different characteristic curves) with different developer/time combinations (each having different characteristic curves) with different lighting conditions (each having a different lighting range). Moreover I am not suggesting that this is necessarily a way to determine exposure for any given scene -- for that the histogram is a far better tool. Regarding film vs. digital: both are fundamentally sensors that turn light/photons into something else -- indeed both sensors cause a change in an electron on receiving a photon. Both also have characteristic curves. One would not expect the characteristic curves to be identical. Jonathan