Pentax K-x Performance, Timings, and Image Quality

November 16, 2009 by Adam Crawford Reads (11,297)

Pentax has built a nice little camera with the K-x, though it does have a few flaws. It is poised to take over the place of the K2000, following the path they pursued with their point and shoots by including HD video capture in every camera. Some advanced functions position the K-x not quite at the entry-level, while at the same time it offers different scene modes and automatic settings, making the K-x on paper seem to be the best of both worlds. For the most part, the K-x is the best of both worlds, but some of what it lacks includes poor power performance, trouble focusing during live view capture, and a somewhat sluggish image buffer.

Shooting Performance
The K-x performed very solidly in our lab tests. We measured shutter lag (press-to-capture, pre-focused) at 0.03 seconds, which is just below the Olympus E-620. AF acquisition (using the viewfinder) came in at 0.25 seconds, while the K-x’s continuous shooting reigns supreme at the top of the pile, at a fast 4.4 fps (slightly slower than the advertised 4.7 fps though).

Shutter Lag (press-to-capture, pre-focused)

Camera Time (seconds)
Olympus E-620 0.02
Pentax K-x 0.03
Canon EOS Rebel T1i 0.04
Panasonic Lumix DMC-GH1 0.06

AF Acquisition (press-to-capture, no pre-focus)

Camera Time (seconds)
Canon EOS Rebel T1i 0.19
Pentax K-x 0.25
Olympus E-620 0.32
Panasonic Lumix DMC-GH1 0.37

Continuous Shooting

Camera Frames Framerate
Pentax K-x 17 4.4
Olympus E-620 6 4.1
Canon EOS Rebel T1i 170 3.8
Panasonic Lumix DMC-GH1 5 2.8

There are three auto focus modes on board the K-x, including AF.S (Single mode) where focus is achieved via a halfway press of the shutter, AF.C (Continuous mode) where the subject is kept in focus after you press the shutter a half click and continues to keep the selected subject in focus, and AF.A (Auto) which switches between the two modes to give you the proper AF mode depending on the scenario. I mostly used AF.A, which worked great for single captures. However, when I used the continuous shooting drive, the AF.C was a requirement.

The AF uses a phase-detection system like most DSLRs, and offers four different options, including Auto 5 AF points, 11 AF points, Select, and Spot. All work well in the field, but the biggest issue we found with the focusing system was in Live View. It worked very hard to find its focus on objects, even in good lighting. Overall, the AF system works well, but does struggle a little bit in low light.

Continuous shooting is top notch. With a 4.4 fps rating, the K-x is completely capable of grabbing a split second frame in the middle of fast-moving action. Other exceptional areas of performance include the Shake Reduction feature, which reduces blur in images. When shooting, I tested out the SR with it on and then off, and it makes a dramatic difference.

Pentax K-x
Shake Reduction off

Pentax K-x
Shake Reduction On

Flash performance is spot on, giving a nice fill with its automatic modes and slow sync. The K-x is even equipped with a wireless flash mode that can set off optical slave flashes.

The biggest deficiency I found in the K-x is the powering system behind it. It uses four AA batteries instead of a rechargeable lithium-ion battery. We have mixed feelings about the AA system – it’s convenient in that you can pick up batteries anywhere, but a DSLR takes a lot of juice to function. Even if you opt for rechargeable AAs, a power-hungry DSLR can run them down pretty quickly.

I advocate that AAs are better suited for point and shoots, but for a DSLR with advanced features, it is bound to be a power hog. In the case of the K-x, it’s true. I went through four sets of batteries during the span of writing my review. The functions that chip away most at the power are use of live view, video capture, flash, and advanced camera processing like HDR and the different digital filters.

Lens Performance
Our K-x review unit arrived body-only, but I was provided with what the kit lens is for the camera – the smc Pentax DAL 18-55mm variable aperture lens. It’s a pretty typical piece of kit glass, though it doesn’t offer much reach for playing with depth of field. Although you can get a pretty shallow depth of field in Av mode, the lens does a reliable job of giving you what you need.

Pentax K-x

The camera’s low-light performance is exceptional, so the glass if more forgivable when you can just bump up the ISO and still get a great low-light shot. This is great when you want an affordable lens like this one, and still want to get good dark shots.

Another great part of the camera body is that you can correct for aberrations that sometimes the lens can cause, and in this case, its inherently going to have some issues like barrel distortion and pin cushioning. Options include in-body distortion correction that works quite well, and also Chromatic Aberration control that helps get rid of purple fringing around the edges of high contrast. All in all, the K-x offers some nice alternatives in-camera to fixing problems in post-processing.

Pentax K-x
Distortion Correction Off

Pentax K-x
Distortion Correction On

Video Quality
There seems to be a problem with Pentax’s rendition of HD video. Earlier this year I reviewed their ultrazoom X70 and the HD video was not good at all. We found all sorts of artifacts and grain in the capture. Video recording in the K-x improves on that, presumably thanks to a bigger image sensor. The video captures detail, but still struggles with the grain issue throughout the frame. The quality is pretty decent, but the noise levels make the video subpar compared to video capture from its competitors.

Image Quality
Image quality at default settings is very faithful to what the eye sees. There is also a cool manual tool for changing the image processing called Custom Image, which allows you to use sliders to change the saturation, hue, high/low key adjustment, contrast and sharpness of your image. Among these preset options with sliders are Bright, Natural, Portrait, Landscape, Vibrant, Muted, and Monochrome.

Other in-camera tools include Cross Processing and High Dynamic Range capture mode. The latter is available in HDR1 and HDR2, offering different levels of processing that create the effect of a wider dynamic range in your final image. What the HDR tool does is take three images simultaneously (one over, one under, and one correct exposure) and processes them together in-camera.

Pentax K-x

Pentax K-x

The digital filters are also unique, giving you everything from a fish eye lens to a toy camera mode. It seems like more and more companies are putting in this camera processing modes to sidestep the digital darkroom edit.

Pentax K-x
Extract Color
Pentax K-x
High Contrast
Pentax K-x
Pentax K-x
Toy Camera

Auto White Balance in the studio shot slightly warm, but in the field worked well under a variety of lighting conditions. Even on a blown out gray day, the AWB gave me the right exposure every time. Although the AWB works great in the field, you still have your pick of WB Daylight, Shade, Cloudy, Fluorescent Light Daylight Color, Tungsten Light, Flash, CTE, and Manual.

Pentax K-x
Auto White Balance, 3200k incandescent light

This brings us to the ISO performance charts, and this is where the Pentax K-x really sings. The ISO range is 200-6400, with expanded options up to 12800. As you can see in the lab samples, ISO 200 all the way to 1600 produce a great image, which is excellent for a 12.4 megapixel image. As I have said before, 12 megapixels is an optimal resolution for an APS-sized image sensor. I’m glad Pentax stepped away from pushing higher resolutions and concentrated on image quality instead.

Pentax K-x
ISO 200
Pentax K-x
ISO 200, 100% crop
Pentax K-x
ISO 400
Pentax K-x
ISO 400, 100% crop
Pentax K-x
ISO 800
Pentax K-x
ISO 800, 100% crop
Pentax K-x
ISO 1600
Pentax K-x
ISO 1600, 100% crop
Pentax K-x
ISO 3200
Pentax K-x
ISO 3200, 100% crop
Pentax K-x
ISO 6400
Pentax K-x
ISO 6400, 100% crop

Even at the 3200 and 6400 ISO settings, you get a workable and usable image, but this is where you start to also see the noise creeping into the cropped image. My field-testing matches right up with the lab test, giving me great images in low-light conditions, mainly due to the ISO performance.

Additional Sample Images

Pentax K-x Pentax K-x
Pentax K-x Pentax K-x
Pentax K-x Pentax K-x

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