The K-7 suffered from arguably sub-par image quality due to it's relatively old sensor; however, the K-5 makes up by delivering best-in-class sensor performance. That's right- the Pentax K-5's sensor scored higher than any other APS-C DSLR when tested by DxO Mark, and it also beat both the Canon 5D Mark II, and the Nikon D700 full-frame models. Most excitingly, the K-5's dynamic range performance seems to be exceptional, with about two stops of expanded sensitivity compared to previous Pentax models. This means that when photographing K-5, more detail will be retained around dark and bright areas of the photograph, resulting is a more natural and easy-to-manipulate image.
While the K-7 only featured a 100-6400 ISO range, the K-5's has been expanded to 80-51200. Not only is its top sensitivity 3 stops higher, but its noise handling has also been overhauled. Through our tests, it appears that the overall image noise levels are over two stops lower on the K-5 than on the K-7, meaning that ISOs as high as 6400 can now "comfortably" be used to deliver high-quality results, and that, at lower ISOs, the K-5's sensor also delivers much clearer images. That's not to say that ISOs beyond 6400 are unusable however, as we were also surprised to see that ISO 12800, 25600, and 51200 still delivered manageable levels of noise. For a more detailed treatment of the K-5's high-ISO performance, please refer to our ISO tests later on in the review. We've also done a side-by-side comparison with the K-7 to illustrate the jump in image quality.
The Pentax K-5 features a 7 FPS shutter- a 1.8 FPS improvement over the K-7. At maximum FPS, the K-7 could take up to 40 JPEGs and 17 RAWs in continuous mode; the K-5 can take about 34 JPEGs and 26 RAWs (after the v1.01 firmware update). We believe that the physical buffer size is the same, and thus, the JPEG capacity is smaller due to the K-5's larger filesize. Firmware improvements account for the increase in the RAW buffer. In "Lo" mode, the K-5 can shoot indefinitely in JPEG at 2 FPS, which the K-7 can do the same at 3FPS. We hope that Pentax can address this through firmware in the future.
One aspect of the Pentax DSLR system that has always been criticized is its autofocus speed. With the K-5, luckily, that's no more! The new SAFOX IX+ AF system, the same that was deployed in the $10,000 645D medium format body, features enhanced focusing algorithms, a more sensitive focusing sensor, and a light wavelength sensor that work together to speed up focusing and eliminate "hunting" as much as possible, especially in low-light scenarios. Through our tests we found the K-5 AF system to be remarkable. As advertised, it focuses faster and more accurately than the K-7, and is comparable to the other brands. We found that SDM lenses still focus slower than comparable screwdrive lenses (by about 10%) , but on the bright side, continuous autofocus for action photography is more responsive and stays on-target, and lamp-assisted focusing in the dark is practically perfect. The camera fires a burst of light, gets close to being in focus, and then fires a second burst and locks on. It only has trouble locking onto surfaces with little contrast, but that is to be expected of all cameras. The K-5 has a dedicated auto-focus assist lamp just like the K-7. It emits a green light aiding autofocus in low light situations. It work s in AF.S mode only, not in AF.C mode.
A few minor changes have been made to the K-5 body, all of which can be seen as being in response to user complaints about the K-7. The mode selection dial has been made bigger so that it is easier to move, the AF mode selection button has been redesigned to be easier to operate, and the RAW button can now be used for more than just switching RAW modes, so that it is of use to photographers who don't care about switching between JPG and RAW functionality. Furthermore, several exciting additions have been made to the firmware, which are described below.