Your raw converter is not set for high dynamic range. There is no such thing as black in a raw file. It just goes from white to noise. The point which is chosen as "black" is entirely a creative choice, though some raw conversion software does not allow the photographer to choose the true raw black point.Originally Posted by Jon Ruyle
Strong contrast and little noise is the most pleasing conversion for most photographs and matches the taste of the most photographers, so the default settings on most raw conversion software are tuned to provide that by setting the black point far above the noise floor and using a tone curve that crushes the shadows.
In other words, the most common conversion is tuned for high contrast and low dynamic range.
If one is interested in utilizing more dynamic range than the typical "high contrast/crushed blacks" conversion, and the photographer chooses their own black point, gamma, and tone curve, it becomes possible to see down to the point where there is nothing but random noise. On some cameras, such as Canon DSLR, the pattern noise becomes a problem long before random noise is reached. Pattern tends to get magnified even further in most raw converters, perhaps because of how it interacts with the edge detection algorithms.
In Lightroom, for example, you can set a "linear" tone curve, "0" blacks, then set shadows to "100" and you should be able to see down into the pattern noise.
IRIS is an exmaple of a raw converter that allows the photographer to have complete control over the black point and true linear exposure compensation. 5.57 is the latest version and it can read 5D2 files. Here's how to do a simple conversion:
File->Open Raw
On the toolbar, find the little icon of the camera, and set it to your model (e.g. 5D2).
Processing->Subtract (enter 1024 for 14-bit Canon cameras such as 5D2, 128 for the 12-bit cameras).
Digital photo->convert a CFA image
To white balance, find a portion of the image that is white, drag a square in it,
Open the console (also an icon on the tool bar) and enter "white"
View->Logarithmic
File->Save (Tiff)
Then open the tiff in Photoshop and analyze the deep, deep shadows. You should see noise (and pattern noise): nothing should be black.
Most people think high ISO has more noise than low ISO, but in the most literal sense that's untrue. It only seems true because photographers tend to reduce light for high ISO and increase light for low ISO. The noise is not caused by the increase in ISO, but the *decrease* in the amount of light. Read noise is reduced at high ISO.
For example, one chooses the f-number for a certain depth of field and shutter speed based on the desired amount of motion blur. The next setting to choose is ISO. Lower ISO for more highlight headroom and more shadow noise. High ISO for less shadow noise and less highlight headroom. In Canon DSLR cameras, that shadow noise includes pattern noise. If, at ISO 100, important highlights are *almost* about to clip, it would be unwise to increase ISO because they would be lost. But if the shadows were more important, then ISO 1600 might be chosen: sacrificing four stops of highlight detail in order to get less noise in the shadows.
We hold these truths to be self-evident, that all photographs are created equal, that they are endowed by their Photographer with certain unalienable Qualities, that among these are Color, Contrast and 12 stops of dynamic range.
That to secure these rights, Raw Converters are instituted among Men, deriving their just powers from the consent of the users, That whenever any Form of Software becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new raw conversion, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Dynamic Range and Contrast. Prudence, indeed, will dictate that Raw Conversions long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the software to which they are accustomed.
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