Pentax K10D vs Sony Alpha A100

Battle of the stabilized 10 megapixels DSLR cameras!

The Sony Alpha A100 and the Pentax K10D compete head-to-head with the most similar feature set among 10 megapixels DSLR cameras. These two digital cameras share the same image sensor, built-in stabilization and dust-reduction. As a matter of fact, these are the only two currently shipping 10 megapixels DSLR cameras with built-in stabilization. Later this year, they will be joined by the Olympus E-510 which has a smaller 2X crop sensor with 4:3 aspect ratio.

Besides the lens mount, the most prominent feature difference is the Pentax K10D's weather-sealed body. Note that weather-sealing is only truly effective when using weather-sealed lenses and Pentax has not shipped any such lenses yet. The first two such lenses, the 16-50 F2.8 and the 50-135 F2.8, are expected to ship in May 2007. Since these are moderately high-end lenses with retail pricing above $800, the weather-sealing feature may not be relevant to all buyers.

The remaining differences between the Alpha A100 and the K10D can be spit into performance features and usability features. Since these camera's share the same sensor, performance differences were not expected to be significant.

Warning: This comparison is about details which make the experience of using each camera different. To some, they may seem picky but when using a camera frequently and under pressure they can matter greatly.

Performance

In our full-review of the Sony Alpha A100, we already showed that the Pentax K10D produces images with noticeably more details starting at ISO 400 and slightly less noise starting at ISO 800. See this in the outdoor crops from the A100 review. Higher-than-average image noise is definitely the A100's more serious weakness.

A camera's performance is not simply about image noise. There are also differences in sharpness, exposure, color, speed, stabilization and dust-reduction. Sharpness is the most difficult to quantify because it depends on both the camera and the lens used. Generally, DSLR cameras produce slightly soft images by default. However, boosting the image sharpness of both the K10D and the A100 to their respective maximums clearly shows that Sony's image processing is capable of producing much sharper images. Indeed, JPEG softness is the K10D's most critical weakness.

The exposure systems of both cameras are excellent. The main difference is that the A100 uses 40 segments for its multi-segment metering compared to the K10D's 16 segments. In practice this translates to more consistent metering for the Sony Alpha. In other words, the A100 changes its metering less when the camera is moved around the same subject than the K10D. In terms of accuracy, both cameras meter conservatively to reduce the chances of burning highlights. That does not mean that they meter identically, since there is no generally no absolutely correct exposure for scenes which exceed a camera's dynamic range. The images below shows a case where the A100 chose a brighter metering and one where the K10D did. This proves that neither camera is consistently more conservative than the other.

Color accuracy varies depending on light sources and a camera's white-balance system. Both the Sony Alpha A100 and Pentax K10D showed very accurate white-balance systems when set manually. When set automatically, white-balance occasionally differs substantially. Under natural light, differences are small but the K10D consistently produced more accurate results. In artificial lighting, the K10D got slightly better results with preset white-balance but often got significantly worst results with automatic white-balance. Overall, the K10D produced better results more often than the A100 while using automatic white-balance. However, when both camera's automatic white-balance failed, the K10D left a much stronger color cast than the A100. Therefore, those who generally leave white-balance on automatic will probably be served better by the Sony Alpha A100.

Speed is great with both cameras. They are both capable of shooting continuously at 3 FPS until the memory card gets full. The way the K10D's shutter-release is designed makes the K10D feel more responsive than the A100. While, this difference is noticeable, it is only a minor difference. For every thing else, both cameras show excellent responsiveness and never leave the photographer waiting.

Clearly, built-in image-stabilization is the most important selling point for these two DSLR cameras. The obvious advantage to built-in stabilization is that it stabilizes all lenses. The disadvantage is that its performance is dependent on the camera. You cannot buy a better stabilized lens if the built-in stabilization is not good enough. Neither Pentax nor Sony, or formerly Konica-Minolta, produce any stabilized lenses anyway. Sony claims that its Super-Steady-Shot system provides 2 to 3.5 stops of added stability. Pentax claims 2 to 4 stops of added stability. After several hundred shots with each camera but before formal testing, the initial impression was that Sony's stabilization worked much better than Pentax. After some Internet research, it was clear that opinions of the K10D's stabilization are much more mixed than opinions on the Alpha A100. Therefore, more formal testing was required.

The effectiveness of stabilization is not systematically measurable because it depends on so many factors including the photographer's movements. Instead, it must be measured empirically. For this we took shots of several targets while varying shutter-speeds and quantified the number of sharp shots. The results showed that the Sony Alpha A100's built-in stabilization performs statistically better and more consistently than the Pentax K10D. However, the difference is less pronounced than anticipated. The table below summarizes the observed results:

There is one small but very important detail which advantages the Sony Alpha A100 with regards to stabilization: the shake-meter. For the unaware, the shake-meter is a 5-point scale visible in the A100's viewfinder, similar to its Konica-Minolta Maxxum predecessors, which indicates relative camera shake. The photographer can use the shake-meter to judge the stability of his body-motion and adjust his posture and breathing to lower the indicated shaking. As such, the A100's stabilization can stabilize the image sensor and the photographer!

The final aspect of performance is dust-reduction. Both cameras perform dust-reduction by shaking their sensors. The difference lies in usage: The K10D has a system menu option to trigger sensor cleaning directly while the A100 has a setup option which cleans the sensor at each power-off. This meant that this Sony DSLR accumulated little dust but going through extra dust-cleanings did not improve things. This Pentax DSLR, however, accumulated more dust and going through several dust-reduction cycles reduced its appearance slightly. In relation to the size of dust particles, dust-reduction worked mostly on small dust particles, like those that can be seen at F11 and beyond. The end result is that both cameras still required manual sensor cleaning and neither was capable of getting rid of the dust that really mattered.

Continued on page 2...