I'm just wondering. Does anybody know the relationship between them?
DocFrankenstein Cream of the Crop  12,324 posts Likes: 13 Joined Apr 2004 Location: where the buffalo roam More info | Nov 01, 2004 12:02 | #1 I'm just wondering. Does anybody know the relationship between them? National Sarcasm Society. Like we need your support.
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daveh Senior Member 318 posts Joined Apr 2003 More info | Nov 01, 2004 12:41 | #2 =
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alansh Member 178 posts Joined Oct 2004 Location: At the foothills of the Pennines More info | Nov 01, 2004 13:45 | #3 Incestuous ? Canon 50D, 40D & 30D + 17-85IS x2, 17-40L, 70-300IS, 28-135IS, Sigma 12-24,Sigma 18-200OS & Sigma 80-400 OS,
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Jesper Goldmember  2,742 posts Joined Oct 2003 Location: The Netherlands More info | Nov 01, 2004 14:04 | #4 They should be the same. Canon EOS 5D Mark III
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slin100 Senior Member 976 posts Likes: 1 Joined Sep 2003 Location: Cupertino, CA More info | Nov 01, 2004 15:15 | #5 The relationship is not quite that straightford. The problem is that the determination of a film's ISO rating is based upon the amount of light necessary to produce a minimum density (0.1) that is generally agreed to produce resolvable detail in the shadows. Digital sensors, being linear devices, don't exhibit the same kind of "toe" characteristics of film. As a result, manufacturers have had quite a bit of leeway in assigning ISO ratings to their sensors. You may very well find that ISO 100 corresponds to two very different sensitivities between two manufacturers. With appropriate electrical or digital gain, a DSC can provide an appropriate output signal level for a range of sensor exposure levels. The maximum exposure level is the exposure level where typical picture highlights will be clipped as a result of saturating the image sensor signal capacity or reaching the camera signal processing maximum signal level. The minimum exposure level depends on the amount of noise that can be tolerated in the image. These situations lead to two different types of speed values, saturation signal based values, and noise based values. The ISO speed is preferably determined using a noise-based method. The saturation-based value is preferably used to indicate the camera's overexposure speed latitude. A second noise-based value is preferably used to indicate the camera's underexposure speed latitude. For some types of DSCs, such as those employing lossy compression methods that significantly affect measued image noise values and cannot be bypassed, it is not possible to correctly determine the noise based ISO speed. In such cases, the ISO speed of the camera is determined using the saturation-based measurement, and the ISO speed latitude values are not reported. In other cases, the noise-based ISO speed may be lower than the saturation-based speed, in which case the saturation based-speed is reported. I suppose the second method could in some way correspond to the method used for film. More from the standard: The ISO speed ratings described in this standard are intended to harmonize with film ISO speed ratings. However,there are differences between electronic and film-based imaging systems that preclude exact equivalency. DSCs can include variable gain, and can provide digital processing after the image data has been captured, enabling desired tone reproduction to be achieved over a range of camera exposures. It is therefore possible for DSCs to have a range of speed ratings. DSC stands for Digital Still Camera, btw. Steven
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photofinish Member  232 posts Joined Sep 2004 Location: Near Hartford, Connecticut USA More info | Nov 02, 2004 09:11 | #6 You might want to check this out for a little more info, too: ---jerry
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