Pentax K-30 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 kit lenses. Sharpness and contrast is very good in the center of the frame at wide-angle, though corners are soft, even stopped down to f/8. Chromatic aberration isn't an issue, as the K-30 suppresses it in JPEGs. Results at full telephoto are also quite good near the center of the frame, but again corners are soft. Chromatic aberration is more noticeable at full telephoto, despite the camera's efforts to suppress it.

Macro
A larger than average macro area with the 18-135mm lens, with good detail. Flash throttled down well.

Like zoom range, macro performance will depend entirely on the lens being used. With the Pentax 18-135mm lens, the K-30 captured a larger than average minimum macro area (for an SLR kit lens), measuring 3.40 x 2.25 inches (86 x 57 millimeters). Detail is pretty good in the center of the frame, though corners are soft, 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-30's built-in flash was tall enough so that the lens didn't cast a shadow, and it throttled down well for our standard macro shot, producing a good if slightly dim exposure.

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

The Pentax 18-135mm lens produced about 1.1 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-30 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-30 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 1.1% barrel distortion in the uncorrected file has been practically eliminated, with less than 0.1% complex (slightly moustache-shaped) distortion remaining. At the telephoto end, the 0.5% pincushion distortion in the uncorrected image was overcorrected to about 0.3% barrel distortion. You can also notice some of the image has cropped away in the process, especially at wide-angle, so keep that in mind.

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

Chromatic Aberration. Chromatic aberration is fairly low at the full wide-angle setting of the Pentax 18-135mm lens, being suppressed by the K-30's JPEG processing. At full telephoto, chromatic aberration is more 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-30 suppresses chromatic aberration in JPEGs by default, as uncorrected images from this lens have much higher amounts (see below).

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 left being slightly softer that others. The blurring extended a small to moderate amount into the frame depending on the corner, but the center was quite sharp. At full telephoto, corners were also quite soft, this time the upper right was a little softer than the others. Again, softness extended a moderate amount into the frame, but the center was quite sharp. Some corner shading ("vignetting") can also be seen from the darker corner crops.

Corner sharpness improved only slightly 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-30 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 (right) at the telephoto end, exacerbated by corner softness. At wide-angle, C.A. wasn't as bad, but still much more than in corrected images. Pentax K-30's processor was effective at removing much of color fringing with Lateral Chromatic Aberration Correction enabled (default), though it still leaves some visible chromatic aberration behind in the form of purple and blue fringes.

Overall, below average performance, though the 18-135mm does offer much more reach than most kit lenses. This lens is sharp in the center, but corners are soft even stopped-down to f/8. Macro performance isn't great, geometric distortion is high at both wide-angle and telephoto, and chromatic aberration is high to very high, though the K-30 can reduce lens aberrations.

Coverage
Good accuracy from both the optical viewfinder and LCD.

The Pentax K-30's optical viewfinder showed just under 99% coverage vertically, and about 98% 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 horizontal shift relative to the sensor. In Live View mode, the LCD showed about 101% coverage vertically, and closer to 100% horizontally. Good performance here.