Originally posted by outsider Sure you can fix all sorts of things on post processing, but that takes time and only improves PERCIEVED quality.
I find the latter half of this statement to be an extremely strange notion. Yes, it takes time to remove noise in a satisfactory way from an image with software, and even if the results are good, it may not be worth it to someone to go through the hassle. And in some cases an image is just going to be too noisy to rescue with software without a notable degradation of overall detail.
But what's this business about "Perceived quality"? What does that even mean? If you are willing to take the time to edit a photo at all you are implicitly stating that the raw produced by the camera is just that - a raw material that you will mold into a final image. If your post processing includes noise reduction, and the result is something that you "perceive" as a beautiful image, can you tell me what exactly you are losing out on?
Unless you are a no-PP purist, any other editing you could possibly do to enhance your raw photo smacks of a strange double standard. For example, is playing with curves to make a more striking, contrasty image merely affecting its "perceived quality"?
You are right though in a sense: the quality of an image is in how it's perceived by the viewer. So who is your audience -- the camera itself? Sadly, all it perceives is electron volts.
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More on the topic of your question: I agree with Wheatfield's assessment. I tend to manually set my sensitivity so I have little experience with the range intermediate between ISO 400 and ISO 800, but somewhere in that gulf there is a large increase in noise. Though I still find ISO 800 quite acceptable because the noise has a grainy quality. By ISO 1600 the noise takes on hideous chromatic characteristics that make it uniquely digital. These images I find to still be rescuable with noise reduction in PP so long as they were exposed well, but there is a noticeable loss of fine image detail by this step.
If you typically shoot under ISO400, I don't think there's much to complain about with the K-7's noise, unless you are trying to pump up the shadows too much, as others have mentioned.