Originally posted by GeneV The Kx has a Sony Sensor that is miles ahead of the Samsung in the K7 or K20d for low light. It was the first Pentax which I could use at 3200 ISO. Newer models have higher resolution and it can be hard to compare, but when I was using both the K3 and Kx, I did not see a big difference in high ISO capability, especially if I use Noise Ninja. The K5II is a little better than either of them.
Not wanting to drift too far from the OP's original questions, however...
I've used a K-r, which had the same sensor as the K-x, I believe. I agree, it's excellent. Compared to later, higher resolution cameras at 100% reproduction, it's surprisingly good. However, for photos viewed at the
same physical size, the effect of down-sampling on later, higher resolution sensor images produces generally better results at higher ISOs in terms of noise (in my own personal experience, at least).
Originally posted by GeneV It is too bad that DPReview’s image comparison tool does not allow a comparison between the Kx and K70, because they changed their test image. However there isn’t much difference between the K3 and K70.
Assuming we're talking about RAW shots, the K-70 shows a noticeable improvement over the K-3, especially where colour noise is concerned. Overall, I'd say there's about one stop of improvement, but at higher ISO settings the colour noise difference is huge.
I'm not saying the K-x is a bad camera - far from it, it's very good. But higher ISO performance on the K-70, for photos viewed at the same physical size, will be better.