The K-5's metering system is all but infallible in everyday shooting situations, but there are times when the dynamic range of your scene may exceed the abilities of its sensor - exacerbated by the very tight highlight range of the default JPEG tone curve. Such a scene is shown below - exposure is correct for the majority of the scene, but the sky is very bright, and shows large clipped areas with almost no detail. As you can see, applying negative exposure compensation to the JPEG file (using Adobe Camera Raw) enhances these areas a little, but not much - there is simply very little tonal information there to recover.
Fortunately, a lot of the lost detail can be recovered when converting RAW files. Here, we applied -1EV exposure compensation to a simultaneously captured RAW file using Adobe Camera Raw, and as you can see, we managed to reveal a lot of the missing detail in the clouds and on the horizon. Pulling this down even further to -1.5EV brings back a tiny bit more, but by this point, channel clipping means that colors in the brightest 'recovered' areas are not entirely accurate. What this tells us is that as usual, the K-5's RAW files contain roughly 1EV more highly dynamic range than its JPEG files.
For maximum highlight dynamic range, you can turn 'Highlight Correction' on, which gives approximately 1EV extra highlight range in both JPEG and RAW files. In fact, we'd recommend that you keep this feature activated by default, since it has little negative impact upon the K-5's performance.
|JPEG - Metered Exposure|
|JPEG -1EV (in Adobe Camera Raw)|
|RAW - Metered Exposure, -1EV correction|
|RAW - Metered Exposure, -1.5EV correction|
Overall Image Quality / Specifics
Our main criticism of the Pentax K-7's image quality was its relatively poor performance at high ISO sensitivity settings. With its newly developed 16MP CMOS sensor, the K-5 is able to far surpass its predecessor's low-light abilities, to the point where we're confident in saying that it offers amongst the best image quality of any current APS-C DSLR.
Our comments about the K-5's abilities almost exactly match those we made about the Nikon D7000, which isn't surprising when you consider that both cameras probably use a closely related sensor. The combination of a high pixel count and exceptionally low noise floor mean that images from the K-5 not only come out of the camera with plenty of detail, they are also unusually malleable. As you will see from the examples at the foot of this page, shadow areas are remarkably clean, and full of genuine detail.
The K-5's sensor is excellent, but naturally it has limits. Whilst ISO 51,200 looks great on a spec sheet, the reality of shooting at this setting is that noise (and noise-reduction) severely impairs critical image quality in JPEG files, and even in RAW mode, this setting should be reserved for emergency use only. Impressively though, JPEG files look good up to ISO 6400 - certainly good enough for most applications - and with a little care and attention, acceptable results can be coaxed from the K-5's RAW files right up to ISO 25,6000.
The only issue to be aware of as far as image quality is concerned, is the occasional appearance of jaggies in very fine diagonal lines, where they appear 'stepped'. This is almost certainly a consequence of the K-5's light AA filter. We saw this clearly in our studio test images (and it is reported here) but it should be stressed that in the hundreds of 'real world' pictures that we took with the K-5, we barely noticed it.
The Pentax K-5's imaging sensor is of a new generation which produces exceptionally low read noise at base ISO. This lowers the noise floor that usually limits DR and means that you can pull much more dynamic range out of the shadows in RAW conversion than you might typically be able to with 'conventional' sensors.
To illustrate this we are comparing the K-5 with the Canon EOS 60D. We have taken the base ISO RAW shots of our studio test scene and developed them in Adobe Camera RAW with a +3.0EV digital exposure compensation to lift the shadows. We've then taken crops in the darkest areas of our scene to compare the level of shadow noise on the both cameras. Applying the digital exposure compensation makes shadow noise more visible and at 100% magnification it becomes clear that the K-5 produces noticeably less shadow noise than the 60D.
|Pentax K-5 - ACR+3.0EV||Canon EOS 60D - ACR+3.0EV|
|100% crop||100% crop|
|100% crop||100% crop|
The 'real world' advantages of this technology are obvious from the example shown above. Underexposure is easier to compensate for post-capture, and a lot of 'hidden' detail can be drawn out of shadow areas (either post-capture or using the K-5's Shadow Correction feature) without worrying too much about noise.
Dynamic range drops off above base ISO, and decreases incrementally as the ISO sensitivity is raised (due to noise swamping the shadows), but an impressive amount of detail can still be drawn out of shadow areas at relatively high ISO sensitivity settings. See the example below, captured at ISO 1600 in JPEG mode.
|Pentax K-5 - metered exposure (JPEG)||Pentax K-5 - metered exposure (JPEG) +3EV exposure compensation in ACR|
|100% crop||100% crop|