I've just acquired a K5, having used a Samsung GX-10 for several years, latterly with a couple of Pentax-A and -M lenses which gave me some lovely images, but which wasn't great above ISO 400-800 and had poor autofocus and only OK metering. I was really looking forward to the low noise / high ISO ability of the K5, as I prefer natural light shots most of the time. I've also just invested quite a lot in some more lenses (Sigma 105 Macro, 35 Ltd macro, and Pentax 12-24 (yet to arrive) so am quite keen to see the benefit of the upgrades.
I was initially very concerned at the 'mushiness' of detail in the K5 images - my wife has fantastic golden hair which is a great resolution test, and this was coming out terribly even at ISO400. See first two examples below (Pentax 55-300 @ 55, flash 1/180s, and then 35Ltd Macro :-) also at ISO400). Even the RAW versions were little better.
I did some focus adjustments with various lenses, and whilst this was successful in addressing some errors (front focus mostly), I was still not seeing the contrast and edge clarity that I expected, and some edge-associated JPEG artefacts were horribly obvious - looked like a point and shoot shot. A friend's Canon 5DII was in a completely different league, under the same (poor) lighting conditions.
I have checked for 'black' noise by making 1sec exposures with the lens cap on at different ISOs, using ImageJ to produce histograms of each RGB channel's values in the resulting JPG - there is a systematic and reasonable variation, with very little noise apparent - but this is on the NR-treated JPGs so perhaps not a good index. I'll have to find a way to get the full 14-bit values from the RAW files - any suggestions?
Before I update the firmware, which may alter the results, I have turned off NR completely, and this has made a substantial improvement - rather a relief, but it's concerning that such a negative impression of the camera's quality can be had using the default settings.
Without NR, things are much better: even at ISO3200 a 100% crop is just a little noisy but without the mangling of all detail that was happening before. The second pair of hair samples below are at 800 and 3200 ISO, using the Sigma105 macro. Much preferable, although the RAWs may yet deliver something even smoother and more natural looking.
It seems that this is a solved problem, but I wanted to ask anyone with more experience and knowledge whether this has been a known issue with the default settings, whether the newer firmwares are better behaved, and what optimum settings for NR vs ISO might look like. I had worried that my K5 was defective in some subtle way (poor a/d, whatever) but my worries are receding - any confirmation that all is well would be very welcome! I hadn't seen this question discussed despite my extensive reading-around before getting the K5. I'm going to update the firmware and re-calibrate the lenses next...
cheers to all, happy new year!
Miles