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A scientific approach to proving whether man landed on the moon - photogrammetric rectification
Brad Guth wrote:
Bob Monaghan recently had this to say: http://groups.google.com/group/rec.p...bbe950330f1dd4 Film Film Dmax Contrast [n.b. 4096:1 is 12 stops] Vericolor 5072 (neg-pos) 3.9 D 8000:1 Kodachrome 25 3.8 D 6300:1 Kodachrome 64 3.7 D 5000:1 Ektachrome 64 3.7 D 5000:1 Ektachrome 100GX 3.8 D 6300:1 Ektachrome 100plus EPP 3.8 D 6300:1 Fuji Velvia 50 RVP 3.8 D 6300:1 Fuji Velvia 100 RVP100F 3.8 D 6300:1 Fujichrome EI 100 3.6 D 4000:1 in short, lots of us work with films which have 12 or more stops of dynamic range. http://palimpsest.stanford.edu/byaut...al-projection/ Brad Guth --------------------------------------- In that same USENET thread there is this reply to the above: From Stephen H. Westin Date:Tues, Nov 30 2004 2:53 pm "....No, it claims that these films are capable of producing densities with those wide ranges. Not the same thing. And it's wrong. They take the Dmax as the contrast range, which isn't true unless Dmin is zero. For example, the Velvia RVP data sheet AF3-960E shows a Dmax of around 3.8 for two of the layers, but only about 3.3 for the red layer. Anyway, the Dmin looks to be about 0.2 for all three layers, so even the green and blue layers are at about 4000:1 contrast, not the 6300:1 listed above. The red layer is about 1300:1 contrast. But I thought we were talking about the exposure range of the film, i.e. the input, not the resulting output. The exposure range to drive the film from Dmax to Dmin is about 3 log units (-2.5 to 0.5), so the range of exposures to which it will respond (with a response that might be detectable in the developed film) is only about 1000:1, or 10 stops. Similarly, Ektachrome EPP shows a contrast range from 2.85 to 3.65 density steps (700 to 4,500), depending on the layer. And its useful exposure range seems to be perhaps 300:1 to 1000:1. Keep in mind that when we talk about Dmax and Dmin, we're not in the realm of good, or even acceptable, photographic reproduction. We're just talking about the information that is theoretically present at some level on the film. You would have to have a very good scanner and some careful digital processing to hope to turn this into something that's actually visible. The page to which you refer is a bit scary; this guy blithely quotes specifications without having measured what happens in the real world. I've measured a video projector with rated contrast of 500:1 or so; its installed performance was about 70:1. Likewise, it's wonderful that film can produce over three orders of magnitude of contrast, but stray light in a real projector limits that to about 100:1. ------------------ Of relevance to this thread: ".....Keep in mind that when we talk about Dmax and Dmin, we're not in the realm of good, or even acceptable, photographic reproduction. We're just talking about the information that is theoretically present at some level on the film. You would have to have a very good scanner and some careful digital processing to hope to turn this into something that's actually visible." |
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