Archived posting to the Leica Users Group, 2006/02/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Thanks for this explanation. Now, I've got to digest this and apply it for myself. Thanks! Scott Jonathan Borden wrote: > Scott McLoughlin wrote: > >> Good info! My JPEG curve is the popular, updated version of >> the old "White Wedding" curve. >> >> In a digital context, how would one "test" ISO. > > > Excellent question. > > Film ISO is measured as defined by the International Standards > Organization. > I suggest that the following method would allow one to develop an > equivalent "ISO" for digital sensors: > > The method that I've used to measure my own "ISO" has been to shoot a > textured grey fabric with a meter at the recommended exposure and > then each frame at a successive underexposure of one stop. > > Using the Zone system, Zone 0 ought be pure textureless black. > consequently the proper "ISO" for a particular film/dev combo ought > be when 5 stops of underexposure give a blank textureless negative. > That is to say the exposed part and the unexposed edge have the same > density (film base + fog). > > 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). > > By this method one could actually compare the DMR with a Canon sensor > -- it may be that Leica is just being more conservative than Canon > regarding the ISO ratings. Underexposing by more stops than is > supported by the sensor is just like pushing a negative -- although > you get a picture you loose shadow detail. > > Do you fault Kodak or Ilford for selling ASA 3200 films that really > have a true ISO rating of 800-1000 (given the film base + fog > measurement technique)? This might be the exact same situation as > Canon allowing a higher "ISO" for the 20D than the Leica DMR. Has > anyone measured this? > > Jonathan > > > >> >> Tim Atherton wrote: >> >>> Bear in mind that the on camera histogram may be a little >>> misleading - it is >>> usually the histogram as applied to a to a JPEG which has had the >>> camera's >>> default conversions applied to it (including a fairly steep S curve) >>> >>> So what you see there has already dumped a lot of the information >>> that would >>> be in the RAW file - including highlight detail >>> >>> Add in - that rather like the old days you still need to tweak the >>> iso of a >>> digital camera (remember shooting slide film at 80 or 125 instead >>> of 100? >>> etc or rating 160 neg film at 125 or 100?) . A digital camera's 100 >>> iso may >>> actually be closer to 80 or 125 - you need to run your own tests - >>> just like >>> the old days :-) >>> >>> tim a >> > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information -- Pics @ http://www.adrenaline.com/snaps Leica M6TTL, Bessa R, Nikon FM3a, Nikon D70, Rollei AFM35 (Jihad Sigint NSA FBI Patriot Act)