Pentax K-x Performance

Very good speed for a consumer digital SLR.

The Pentax K-x's startup and shutdown times are about average for an SLR. Buffer clearing time depends on the image size and quality, burst length and how fast the card is.

Mode switching time is good for an SLR, though switching from Record to Play was a bit on the slow side.

Full autofocus shutter lag using single-point (center) AF mode is excellent, at 0.097 second with our reference Sigma 70mm f/2.8 lens. Switching to auto-area AF mode increased lag slightly to 0.122 second, but that's still very fast for a consumer model. Enabling the flash increased the lag to 0.225s, which is still very good. "Pre-focus" time is also quite fast, at 0.082 second (pre-focusing means half-pressing and holding down the shutter button before the final exposure). Continuous autofocus lag and Manual focus lag weren't much slower than prefocused, at 0.083 and 0.082 second respectively.

As expected, Live View mode shutter lag was a lot slower than using the optical viewfinder. Using Phase-Detect mode, full autofocus lag averaged about 0.448 second with our Sigma 70mm f/2.8 reference lens. That increased to 2.57 seconds when using Contrast-Detect mode. Prefocused, Live View mode shutter lag was a tolerable 0.427 second.

To minimize the effect of different lens' focusing speed, we test AF-active shutter lag with the lens already set to the correct focal distance. We also use the same Sigma 70mm f/2.8 macro with every camera (on all platforms except Four Thirds/Micro Four Thirds and Nikon consumer models lacking an in-body focus motor), to further reduce variation, and because our tests showed that focus-determination time with this lens was close to the fastest, across multiple camera bodies from different manufacturers. Being an older design with a non-ultrasonic motor, it wouldn't be the fastest at slewing from one focus setting to another, but that's exactly the reason we measure focus determination speed, which is primarily a function of the camera body, vs focus adjustment speed, which is primarily a function of the lens.

Shot-to-shot cycle times are very good for a consumer SLR, ranging between about 0.3 and 0.4 second, depending on the image quality setting. Continuous speeds are also quite good, at about 4.3 to 4.6 fps, depending on the image quality in Continuous Hi mode. JPEG buffer depth is pretty good too, at 25 Large Fine JPEG frames. This drops to 5 and 4 frames in RAW and RAW + LF JPEG modes respectively. (Note that our target image for this test is difficult to compress, so you'll likely get longer bursts with more typical subjects.) The flash takes 3.3 seconds to recharge after a full-power shot, which is also pretty good.

Connected to a computer or printer with USB 2.0, download speeds are very fast as well.

Bottom line, the Pentax K-x is pretty fast in just about every aspect of its operation. Continuous mode speeds are best-in-class, and shutter lag and cycle times are quite fast, too. Very good performance overall for an entry-level model.

Battery
Below average battery life with rechargeable NiMH batteries.

The Pentax K-x uses four AA-type batteries for power, and ships with a set of ordinary alkaline cells. Battery life is below average when using the optical viewfinder, and will most certainly be much less when using the LCD in Live View mode. We strongly recommend you pick up a couple sets of rechargeable NiMH batteries and a good quality charger, as they'll save you many times their cost over the life of the camera. We found, however, that the K-x didn't work well with one our favorite brands on NiMH batteries, Sanyo Eneloops, sometimes reporting low batteries when fully charged. We instead used disposable Lithium batteries for our testing. (Note: Pentax has released a firmware update (version 1.01) which corrects this issue. After the update, our Eneloop NiMH batteries worked fine. You can download the firmware update here.)

The table above shows the number of shots the camera is capable of (on either a fresh set of disposable batteries or a fully-charged rechargeable battery as appropriate), based on CIPA battery-life and/or manufacturer standard test conditions.

(Interested readers can find an English translation of the CIPA DC-002 standards document here. (180K PDF document))

Storage
The Pentax K-x accepts SD/SDHC memory cards, and no card is included with the camera.

We strongly recommend buying either a large capacity SDHC card, at least a 2GB card, preferably a 4-8GB one, to give yourself extra space for extended outings. (Check the shopping link above, cards are really cheap these days, so no reason to skimp.)