Pentax K-x Digital Camera Review

Noise Reduction

We used the default configuration for high ISO noise reduction in our testing, but the K-x offers some flexibility here. By default, high ISO noise reduction kicks in after ISO 800. However, through a custom menu setting, you can choose the setting to start applying noise reduction.

The noise reduction processing does have a significant impact, cutting visible noise by nearly half at ISO 1600.

We break down overall image noise into its component parts, red, blue, green, yellow and chroma (gray). If noise in one color channel is considerably higher than the others it can make noise visibility worse, but that's not the case here. More on how we test noise.

ISO Options

Available standard ISOs range from 200-6400, with an expanded ISO range from 100-12800. There's an Auto ISO mode, which allows the user to limit the highest acceptable setting anywhere from ISO 200-12800.

Focus Performance

The K-x incorporates a significant autofocus system improvement over the K2000 introduced earlier this year. The camera now uses 11 autofocus points (versus 5 for the K2000) and offers four AF point selection modes: the camera can choose from 5 or 11 points, the user can select one of 11 points manually, or the center point can be set in spot mode.

Autofocus speed isn't lightning-fast, but it's not bad — certainly up to the task for day-to-day shooting, and even sports photography works reasonably well, particularly when using continuous focus mode.

If you're trying to snag a sharp shot of a moving subject, catch-in focus is available. You set the focus on a point that the subject will pass and hold the shutter button halfway. When your quarry appears and is in focus, the shutter trips automatically.

The camera doesn't have a dedicated autofocus assist lamp, relying instead on a brief burst of light from the pop-up flash to help achieve focus in dark environments. Fortunately, the system works quickly enough in most low-light conditions even without the flash assist, so you'll be able to take your indoor candids without being branded a flasher.

Long Exposure

Our long exposure testing combines color accuracy and image noise analysis at slow shutter speeds (between 1 and 30 seconds), at low light levels. The K-x didn't fare badly in the noise component, but its bright light color problems carried over when the lights were low, leading to a mediocre overall score. More on how we test long exposure.

The good news is that the color didn't shift when the shutter speed changed — consistency here is a virtue — and there was only slight oversaturation. However, the color hues weren't reproduced accurately, leading to a low score here. As expected, results were very close whether long exposure noise reduction was turned on or off.

Image noise results aren't great, but at under 1% across the shutter speed range the images are certainly useable. As we often find, long exposure noise reduction had no positive effect, and doubled the elapsed time for each shot. Long exposure noise reduction systems work by taking a second exposure with the shutter closed, determining the noise pattern in that shot and mathematically removing these flaws from the original. However, since most image noise is unpredictably random from shot to shot, the system rarely works and, in fact, often increases visible noise.

The Panasonic GF1, with its noisy Micro Four Thirds sensor, posted a slightly lower score than the Pentax K-x, but all of the other comparison cameras (including the non-video Pentax K2000 model) posted higher scores in our long exposure test.

Video: Low Light Sensitivity

Testing the Pentax K-x with its kit lens, the camera didn't do a very good job with low light sensitivity. Still, compared to some of the abysmal results we've gotten from other video-capable DSLRs, the K-x's numbers don't look too bad. The K-x required 23 lux of light to register 50 IRE on our waveform monitor. Of the DSLRs we compared it to below, only the Nikon D5000 had a better low light sensitivity (the Panasonic GF1 and Canon T1i were just slightly worse than the K-x).