Gonz wrote:
Not quite accurate, but close. There is still an amplifier there. Just multiplying the digital values you get will result in posterization at the shadow end, its math. You can't create information out of nothing. If you only have 2 bits of information (4 values), then the digitization can only result in 4 values, no matter what you multiply it by. What they mean by ISO invariance is that the sensors are so good noise-wise that those 4 values will be extremely consistent (less random/noisy) and will compare favorably with the amplification by the analog amp. The analog amp will however, result in many more values, albeit noisy. I.e. the conclusion is you can take the best pictures by utilizing as much of the histogram as possible. Its just not realistic to take all your pictures at ISO 100 and compensate in Lightroom.
Yup, theory and practice. In practice, Lightroom is only good for compensating by a few stops. With the K100 and K20, when shooting in low light I was ruled by the histogram, with the K-5,3,1 it guides me. I know that I can give a lot more latitude when under exposing to preserve highlights. When shooting static scenes, I'll bracket rather than carefully chimp each histogram, although bracketing ISO is pretty much useless. I wish the camera let me choose what to bracket independent of metering choice.
A lot of theory and advice have been given in this thread. In theory, theory in practice are a lot closer than they are in practice. The only way to learn what works for you, and your camera, is to try it. It's best if you can try it on some photos that it doesn't matter if you ruin.
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