I almost always shoot my K-x at ISO 100 because, as others have noted, the clean shadow detail it provides is fantastic. There is a slight drop in highlight headroom, but the increase in shadow detail is enough to result in a noticeable net gain in usable DR. I particularly appreciate this in high-contrast landscape situations. You just expose to preserve the highlights and the shadows take care of themselves. Even if half the picture looks black on the LCD, when you open up the RAW files the data is all there and ready to work with.
However, I don't agree that the designation of ISO 100 as an "expanded" ISO is a feature oriented towards new users. It is in fact an artificial ISO produced by extrapolation of sensor data. Falk Lumo did some in-depth analysis of the RAW data from the K-x sensor a while back, and found that Pentax was doing something novel with the sensitivity curve that managed to hold on to the highlights for the most part while really opening up the shadows, in contrast to previous cameras which had "expanded" low ISOs that gained extra shadow detail and lower noise but at the expense of a large chunk of highlight headroom and tonality.
In my opinion, whatever technological magic they worked to accomplish this was in fact the biggest unsung advancement to be found in the K-x. I now lust after a chance to see firsthand what it can do with the K-5's sensor.
Originally posted by Shellinaya 
Similar Threads 
