Sunday, November 24, 2013

Pentax K-3: High ISO


The Pentax K-3 is an interesting, albeit, off-the-beaten path alternative for any long-suffering photographers waiting fore the fabled Nikon D400 or Canon EOS 7D Mark II. However, this latest APS-C DSLR from Pentax (now owned by Ricoh) has many headline features that appeal to aficionados of semi-professional crop sensor cameras:

  • 24.4 megapixel APS-C CMOS sensor
  • Sensor-shift image stabilization, including rotational compensation
  • Anti-aliasing can be turned on/off 
  • 27-point AF, 25 of which are cross-type
  • 8.3 fps continuous shooting


General Usage



Though it's heavier than the Nikon D7100 (675g), the Pentax body doesn't necessarily handle as heavily as its 800g would suggest. To put that in perspective, a Canon 5DmIII body weighs in 860g. Compared to the D7100, the K-3 is a little bit narrower and  doesn't sit as tall. The grip is much more substantial than on the Nikon or perhaps the Canon EOS 70D. There's a lot to hold on to without making the camera feel bulky. Coming from the vantage point of somebody who uses primarily Nikons (and occasionally Canons), much of the Pentax controls are logically laid out and make sense. Though it comes down to preference, switching to a Pentax from a Nikon possibly requires less re-learning than switching from a Nikon to a Canon.

Autofocus behaviour seems merely good, but in unscientific usage, it seems not as fast or consistent as the Nikon D7100, and definitely not as fast and sure-footed as the Canon 7D. Though 27 AF-points is a step up from the K-5II, 25 of them are confined to the center of the frame. Only the two (linear, non-crosstype) points make it it to the 1/4 mark of the frame. For composition, this is a mild annoyance, as the out AF points of center group don't quite make it to the 1/3 mark of the frame (horizontally) for rule-of-thirds composing.

Image Quality


To be fair, the only lens that was available at the time of shooting as the DA 18-55mm F3.5-5.6 AL WR. It's a decent kit lens, with the added bonus of weather sealing, but the off-center performance is nothing to write home about. The following shows the progression of the image noise through the higher ISO range; the camera would certainly be capable of more detail with a prime lens and the refrigerators dead center in the frame. First, the overall scene; all images are from out of camera JPEG's, default settings.


ISO 100, f/3.5. 1/30s, 18mm

Many cameras struggle with this mall courtyard scene, especially with the white balance.  The metering seems a bit on the conservative side and a bit underexposed, but overall, even though the colour temperature could be better, there isn't anything overtly off about the colour balance per say. Cropping in on the refrigerators, this is what the image texture looks like as the ISO climbs:

ISO 100
ISO 1600

ISO 3200
ISO 6400
ISO 12,800





Given the constraints of shooting with the kit lens at wide angle and wide open, the amount of detail that the K-3 can produce is excellent, with sharp edge acuity, even with the smaller objects in the scene. As with any APS-C camera, the comfort level for quality shooting lies somewhere between ISO 1600 and 3200; any higher than that and you would be shooting with greater care, and certainly not cropping in as tightly as this. Though ISO 3200 still produces usable detail, the dynamic range is beginning to suffer (the highlights on the pop bottles get harsher as the ISO climbs.)

As with the Nikon D7100, the removal of the anti-aliasing filter makes the images appear slightly noisier than what you would expect, but this is because the sensor is more faithfully recording the photon shot noise than in a camera with a filtered-sensor. This will clean up with noise reduction, but of course, at the minor expense of detail and contrast. There's a fairly stark difference between ISO 3200 and ISO 6400; the latter would only be good for emergencies and in situations where the subject fills a large portion of the frame, without any critical fine detail. (You can have a look at the D7100 high ISO capability here, but those images are not directly comparable to the ones above.) Though banding noise wasn't on the to-do list for this post, there doesn't appear to be any visible traces of it in the dark portions of the refrigerator doors. In fairness, even though the D7100 is more prone to it than recent sensors, even it too would not be objectionable under the same circumstances.

Generally, you see the same benefits with the K-3 as you do with the D7100; lots of detail with images that require less sharpening than with conventional image sensors. This comes at the expense of more "texture" in the images, but only with you view at 100%. Comparing images at the same magnification yields superior results than with the 16mp cameras. Overall this is a promising camera, but as always, the lens selection becomes a bigger factor when making the decision to switch from another system. If you already have a K-5II, it might not be as compelling an upgrade, but on the whole, this camera is unassuming, competent and gives good value for the serious-enthusiast buck.



With thanks to Broadway Camera.



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