The K-x includes a couple of interesting features. In addition to the traditional program, aperture-priority, shutter-priority and manual exposure modes, Pentax offers a 'sensitivity-priority' option, which automatically adjusts the shutter speed and aperture as you scroll through a user-determined range of ISO sensitivity values. It's a good alternative to the trial-and-error approach to finding the lowest ISO sensitivity that will deliver a desired exposure. There are also other veteran Pentax features like 'catch-in focus' and the effects filter introduced with the K-7.
An auto high-dynamic-range feature combines three sequential exposure-bracketed shots into a single JPEG. But, unlike competing implementations from Sony, for example, it's not really effective as a simple way of producing better low-light images -- shake reduction is automatically turned off and the camera doesn't seem to do any advanced alignment of the images. Even at a fast shutter speed, there's significant camera shake, so you can only use it on a tripod.
For the most part, the K-x is very fast. It takes 0.7 seconds to turn on and shoot, which is quite slow but not too bad. The time taken to focus and shoot in good light is a zippy 0.3 seconds, increasing to only 0.5 seconds in low light. Two sequential JPEGs run at 0.4 seconds, with a slight bump to 0.6 seconds for raw. The camera's 1.2-second shot-to-shot time with flash is the only real cloud in the K-x's speed sky, although Sony models generally perform worse in this regard. The typical continuous-shooting speed is a solid 4.2 frames per second.
Unfortunately, the K-x's image stabilisation is something of a letdown. For whatever reason -- excessive mirror slap vibration, a stiff shutter or simply a poor implementation -- we had plenty more photos with camera shake, even at high shutter speeds and modest focal lengths, than we're used to seeing these days. Furthermore, the LCD display is fairly coarse, which makes it hard to accurately judge if photos are sharp enough. It's also difficult to see the display in direct sunlight. And, as is typical for all but Sony's dSLRs, the live-view autofocus is pretty slow.
Turn the noise down
The K-x is capable of shooting excellent photos. It has a very good noise profile for its class, including well-balanced noise reduction in JPEG files. You can start to see some degradation of detail in shadow areas at ISO 800, but we found the images quite acceptable even as high as ISO 1,600. By ISO 3,200, the decrease in detail becomes obvious.
Pentax rightfully considers ISO 12,800 (and ISO 100) an expanded mode, although we'd probably add ISO 6,400 to that as well. Although there's still usable detail at ISO 3,200, noise and noise-reduction artefacts are obvious by ISO 6,400, even when scaled down.
We wouldn't recommend using ISO 12,800 as a rule, but it's actually pretty good. You lose much of the shadow detail and there's obvious blotchiness, but photos retains good saturation and are more than acceptable for Web use at small sizes. The K-x maintains good colour consistency across all ISO sensitivity levels.
Pentax's 18-55mm kit lens doesn't display much distortion, and the body's optional internal distortion correction does a pretty good job of fixing what little there is. On the other hand, the lateral chromatic-aberration adjustment option didn't seem to fix much at all. Overall, it's a generally good kit lens.
Although the K-x's default 'bright' image setting produces a slight colour shift over neutral, despite ostensibly bumping up only the contrast and sharpness, it's not nearly as severe a shift as in Sony's comparable models. Unlike Sony, Pentax also provides a 'natural' option. Pentax's automatic white balance normally tends to be on the cool side, however, which results in an overall colour cast.