Archived posting to the Leica Users Group, 2006/12/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Walt and others... have you shot C41bw 400, at 800 with normal development? Results? I see this now as advantageous, have never done it, but I plan to try.... thankjs, Steve On Dec 8, 2006, at 6:41 AM, Walt Johnson wrote: > I think I'll start shooting all my Tri-X at 666 ISO. BTW has anyone > noticed the change (years ago) from ASA to ISO appears useless? > > Henning Wulff wrote: > >>> Doesn't it have something to do with logging rhythms. in .3 >>> increments? >>> >>> Henning Wulff wrote: >>> >>>> At 10:29 PM +0100 12/6/06, Philippe Orlent wrote: >>>> >>>>> I was just remembering my ISO scale on the back of my MP: >>>>> 50-100-200-400-800- etc. >>>>> >>>>> But the zones in between are divided in 3 parts. >>>>> >>>>> So between 50-100: 50/3=16,7 >>>>> Between: 100-200: 100/3=33,33, which would put 160 at 100 and >>>>> 2/3ds >>>>> Two full stops under brings us at >>>>> 400 and 2/3ds >>>>> Which is 400 + (800-400)x2/3= 666,7 >>>>> >>>>> I may be wrong, but it looks like Leica logics to me. >>>>> :-) >>>>> Philippe >>>>> >>>> >>>> ISO is not continuous. It's only defined for the discrete >>>> progression (from 100 to 3200) for 100, 125, 160, 200, 250, 320, >>>> 400, 500, 640, 800, 1000, 1250, 1600, 2000, 2500, 3200. >>>> >>>> No numbers in between, ie, there is not 'ISO 300' or 'ISO 666'. >>>> >> >> ISO combines the old ASA and DIN scales, and makes the measurement >> methods and ratings equivalent. DIN was logarithmic while ASA was >> arithmetic, with 400 ASA = 27DIN, 320 ASA = 26 DIN. For every step >> the ASA took an arithmetic step, and DIN took a logarithmic step. >> Different measurement methods meant that there wasn't a complete >> equivalency, but then they got together and came out with the ISO >> method and scaling, which allows for both an arithmetic and >> logarithmic scale. So now the old 400 ASA is approximately ISO >> 400/27. >> >> Both systems jump in discrete, defined steps with intermediate >> values undefined. >> > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information