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Jay DeFehr |
23:05 9 Apr 06 |
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David Eisenlord |
11:57 5 Feb 06 |
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Steve Nicholls |
17:03 24 Jan 06 |
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David Jade |
11:11 25 Jan 06 |
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Re: .1 above base fog or approximate CI ? |
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Phil Davis |
9:28 26 Jan 06 |
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Steve --
Let me refer you to the book (4th ed) page 92, "Calibrating Film Curves" for a detailed discussion of speed point location.
You've already discovered the characteristic difference in speed resulting from speed point change—the advantage for contrasty subjects (SBR=8 or more) increasingly in CI's favor. CI's other advantage is more subtle; it tends to keep image gradation more uniform, as SBR changes, by relating toe density to curve gradient. The 0.1 speed point location was chosen as the standard density for the specific conditions of the ISO test procedure (x=1.3, y=0.8). In other words, it's a one-size-fits-all arbitrary number that ignores the fact that most photographic subjects are not "standard."
The visual differences in print images will be subtle, and related to materials' characteristics to a considerable degree. You can get a good idea of what to expect by using the Matcher to display comparable print curves and watching for mid-tone shifts as you change the film's speed point location and vary the SBR. For gleaning this sort of information the Matcher beats the heck out of field tests.
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Steve Nicholls |
16:47 26 Jan 06 |
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Sandy King |
7:12 4 Mar 06 |
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Phil Davis |
10:21 4 Mar 06 |
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Sandy King |
10:39 4 Mar 06 |
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Jorge Gasteazoro |
12:54 14 Jan 06 |
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