Pentax K-5 II Optics

Zoom
A longer than average kit lens, with below average performance.

With a generous optical zoom ratio of 7.5x, the Pentax 18-135mm lens offers greater telephoto reach than typical 3x zoom kit lenses. Sharpness and contrast were very good in the center of the frame at wide angle, though corners were soft, even stopped down to f/8. Chromatic aberration was quite high, though the K-5 II can suppress it in JPEGs (see below). Performance at 31mm and f/8 was actually pretty good, with very good sharpness over much of the frame and just a touch of softness in extreme corners. Chromatic aberration was lower but still visible in corners and along edges. Results at full telephoto were good near the center of the frame at f/8, but corners were quite soft extending deep into the frame. Chromatic aberration was very high and quite noticeable at full telephoto.

Macro
A larger than average macro area with somewhat soft detail. Flash overexposed at closest range.

Like zoom range, macro performance will depend entirely on the lens being used. With the Pentax 18-135mm lens, the K-5 II captured a larger than average minimum macro area (for an SLR kit lens), measuring 3.50 x 2.32 inches (89 x 59 millimeters). Details were a bit soft in center of the frame and corners were softer, and there's also some noticeable shading ("vignetting") in the extreme corners. (Most lenses have some softening and shading in the corners at macro distances.) The Pentax K-5 II's built-in flash was tall enough so that the lens didn't cast a shadow, but it didn't throttle down well for our standard macro shot, producing an overexposed image.

Geometric Distortion
Higher than average distortion at wide angle and telephoto with the 18-135mm lens.

The Pentax 18-135mm lens produced about 0.9 percent barrel distortion at wide angle, which is well above average and noticeable in its images. At the telephoto end, there was about 0.5% pincushion distortion, also higher than average and noticeable in some shots. Geometric Distortion is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).

Distortion Correction
The Pentax K-5 II offers optional Distortion Correction when using DA, DA L, and DFA lenses, as well as several of the company's FA Limited lenses.

The Pentax K-5 II does not apply any geometric distortion correction to JPEGs by default. There is however a menu option to turn Distortion Correction on. RAW files are not corrected, but are tagged to have the same correction applied when using a RAW converter that supports the embedded parameters.

The crops above show JPEGs taken with the kit lens at wide angle and telephoto with Distortion Correction enabled. As you can see, the 0.9% barrel distortion in the uncorrected file has been slightly overcorrected to about 0.2% complex (slightly moustache-shaped) distortion. At the telephoto end, the 0.5% pincushion distortion in the uncorrected image was overcorrected to about 0.2% barrel distortion. Also notice some of the image has been cropped away in the process especially at wide angle, so keep that in mind.

Chromatic Aberration and Corner Sharpness
High to very high levels of chromatic aberration from the 18-135mm lens in JPEGs. Very soft corners at both wide angle and telephoto.

Chromatic Aberration. Chromatic aberration was high and fairly bright in the corners at the full wide angle setting of the Pentax 18-135mm lens. At full telephoto, chromatic aberration was even higher and brighter, and quite noticeable. (This distortion is visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.) The Pentax K-5 II has the capability to suppress chromatic aberration in JPEGs (see below), however this is disabled by default.

Corner Sharpness. The Pentax 18-135mm lens produced soft corners at full wide angle and full telephoto when shot wide-open at maximum aperture. All four corners were soft at wide angle, with the lower right slightly softer than others. The blurring extends a small to moderate distance into the frame depending on the corner, but the center was reasonably sharp. At full telephoto, corners were also quite soft, with upper corners softer than the lower ones. Softness extended quite far into the frame, and the center was also a bit soft.

Corner Shading. Moderate amounts of corner shading ("vignetting") can also be seen from the darker corner crops, particularly at wide angle.

Stopped-down to f/8. Corner sharpness improved when stopped-down to f/8, but they were still soft, particularly at telephoto. Chromatic aberration remained about the same, perhaps slightly lower and not quite as exacerbated by the blurring in the corners. Corner shading improved quite a bit, though.

Chromatic Aberration Reduction
The Pentax K-5 II offers lateral chromatic aberration reduction for the same lenses that are supported for distortion correction.

As illustrated in the crops above, the 18-135mm exhibits some very high lateral chromatic aberration in the corners when uncorrected (left) at the telephoto end, exacerbated by corner softness. At wide angle, C.A. wasn't quite as bad, but still much more than in corrected images. Pentax K-5 II's processor is reasonably effective at removing much of color fringing with Lateral Chromatic Aberration Correction enabled, though it still leaves some visible chromatic aberration behind in the form of magenta and blue fringes.

Overall, below average performance, though the 18-135mm does offer much more reach than most kit lenses.

Coverage
Good accuracy from both the optical viewfinder and LCD.

The Pentax K-5 II's optical viewfinder showed just over 99% coverage vertically, and just under 99% coverage horizontally with our Sigma 70mm f/2.8 prime lens. That's a little short of Pentax's 100% coverage specification, and there was also a slight tilt relative to the sensor. In Live View mode, the LCD showed just under 99% coverage vertically, and closer to 98% horizontally. Good performance here.