Pentax K-r Optics
Pentax K-r Optics
The Pentax K-r has an APS-C sized sensor which is smaller than 35mm film, so it's designed to work with DA lenses as well as full-frame lenses. DA lenses tend to be smaller and lighter than full-frame models with the same focal length and maximum aperture. The sub-frame sensor on the Pentax K-r means that it has a smaller angle of view (by a factor of approximately 1/1.5x) than a full-frame camera with any given lens. While most properly called a "crop factor," the ~1.5x ratio is most commonly referred to as the "focal length multiplier," since that's how it works in practice: Any lens used on the Pentax K-r will have the same field of view as one with a ~1.5x greater focal length will when attached to a 35mm camera. For example, a 100mm lens on the K-r will show about the same field of view as a 150mm lens on a camera with a 35mm frame size.
It's important to note that while some of Pentax's lens models -- those with a DA * or WR designation -- are weather sealed, the K-r body isn't. Hence while these lenses will certainly still function on the K-r body just fine, the combination won't provide water or dust resistance.
The table below (courtesy of Pentax USA), details the K-r's lens compatibility with the various types of Pentax lenses.
The SAFOX IX AF module's optics have improved transparency, which the company says translates to improved performance in low light. The AF module's optics also have better controlled aberration, improving autofocus accuracy. Ambient temperature, says Pentax, has less of an impact on the SAFOX IX module. Sharp-eyed readers will note that the K-r's SAFOX module lacks the "+" designation, which features in the 645D, K-7, and K-5. This hints at one important feature that differentiates the mid-range K-r from its prosumer and pro siblings. Like the K-x model before it, the Pentax K-r's AF system lacks the secondary light color sensor that allows the 645D, K-5, and K-7 to determine the light source type. It hence cannot take this into account when determining focus.
When using autofocus, you can magnify the image 2x, 4x, or 6x by pressing the INFO button, and this defaults to being centered around the autofocus point. The four-way controller can be used to move the magnified area around the frame, and if set to Contrast Detection AF, the focus point moves so as to remain in the center of the view. The green button is used to immediately return the view to the center, and for Contrast Detection AF, likewise resets the AF point to the center of the frame. Unless already zoomed in to the maximum 6x, when using Contrast Detection or Face Detection AF, the view will smoothly zoom in to a 6x view centered on the point of focus during AF operation, and then return to a full image view shortly after an AF lock is achieved. This is great for static scenes, providing an intuitive view of where the point of focus lies, but unfortunately it can't be disabled, and applies even when you'd expect a moving subject -- such as when continuous autofocus is enabled -- making it quite tricky to keep moving subjects within the image frame during Contrast Detect AF operation.
When manual focus is used, an even higher degree of magnification is available, up to a maximum of 10x zoom, as an aid to focusing. This defaults to the center of the image frame, but can again be positioned anywhere within the image.
Although the AF assist lamp can be enabled or disabled through the Custom Function menu, enabling it doesn't guarantee that it will illuminate in all shooting conditions. Instead, it's left up to the camera to decide whether or not it needs help from the assist lamp to determine focus. In our experience, we found it only illuminated in relatively low light conditions.
The Shake Reduction function is enabled or disabled through the Control Panel display or page four of the Record menu, and the K-r will automatically display the Shake Reduction menu if the camera has no feedback from the lens. Note that Shake Reduction isn't recommended for tripod shooting, and will automatically disable in the self-timer modes, remote control modes, Bulb mode, HDR mode, and when using a wireless flash. It's also not recommended when using very low shutter speeds. Unlike the system used in the Pentax K-7 (but in common with every other sensor-shift camera on the market), the K-x's shake reduction doesn't correct for rotation, only for horizontal and vertical motion.
The drawbacks to sensor shift Shake Reduction technology as used by Pentax and several other companies are twofold. One is that you can't see its effects as you look through the optical viewfinder, as you can with Canon and Nikon's lens-based stabilization systems. But thanks to the Pentax K-r's Live View mode, you can indeed see the effect on the LCD, and SR seems to be pretty solid and effective. The other potential disadvantage is that sensor shift designs aren't necessarily as effective at correcting for shake on lenses with longer focal lengths, compared to lens-based stabilization. At least one third party does offer lens-based stabilization for Pentax digital SLRs, so the potential is there to simply disable the body's own shake reduction and use the lens's stabilization if available, giving Pentax users the best of both worlds: lens-based stabilization for long focal lengths, and body-based to allow stabilization with the remainder of the user's lens collection -- at least, if they're willing to consider third party glass.
While dust removal systems can increase the interval between manual cleanings, it bears noting that no such system system can completely eliminate the need to occasionally clean the sensor manually. Copper Hill Images is an advertiser of ours, but we'd recommend their wet/dry cleaning system even if they weren't (it's what we use in our own lab): See the Copper Hill website for details.
Distortion / Lateral Chromatic Aberration Correction. The Pentax K-r can correct for both lens distortion and lateral chromatic aberration in-camera, when using DA, DA L, D FA, and some FA lenses without any accessories between the lens and camera body. This is a feature usually found on more expensive camera models, and Distortion correction corrects both pincushion and barrel distortion for all except the DA Fish-Eye 10-17mm lens, helping ensure lines that should be straight appear so in the final image. Lateral chromatic aberration correction aims to fix color fringing and blurring which can be especially prominent with some lenses toward the corners of the image. While they're only relevant to Raw shooting if you're using Pentax's bundled Digital Camera Utility 4 software or processing the images in-camera, JPEG shooters gain the benefit of both corrections regardless of the software they're using on their computer. Both corrections slow down the camera's burst shooting capabilities significantly, though this need only be an issue for JPEG shooters. Raw shooters can leave both effects disabled at capture-time to improve the burst speed, and then later apply them in images that require correction when developing the Raw files in-camera.
Pentax K-r Optical Test Results
The Pentax K-r is sold body-only, or bundled with the DA L 18-55mm f/3.5-5.6 AL kit lens. Below are the results of our optical tests on the Pentax K-r with the optional kit lens. The studio test shots on other pages of this review (apart from the flash range shots) use a very sharp, reference prime lens (Sigma 70mm f/2.8 EX DG Macro). Gallery shots were taken with the sharp Pentax DA 17-70mm f/4 AL SDM.
Fair performance with the Pentax 18-55mm kit lens.
|18mm @ f/8||55mm @ f/8|
As mentioned previously, the Pentax K-r is sold body-only or bundled with the Pentax 18-55mm f/3.5-5.6 D AL kit lens. The Pentax 18-55mm lens offers a typical optical zoom range of ~3.1x for an inexpensive kit lens. Sharpness was fairly good across the frame at full wide-angle (stopped down to f/8), with low levels of coma distortion, but strong chromatic aberration as well as some minor softening was visible in the corners. Results at full telephoto were fair with sharp detail on the right side of the frame and much lower levels of chromatic aberration, but the bottom left quadrant of the frame was a little soft.
Average sized macro area with the 18-55mm lens, with soft detail. Flash worked well up close.
|Macro with 18-55mm kit lens
55mm @ f/8
|Macro with Flash
55mm @ f/8
Like zoom range, macro performance will depend entirely on the lens being used. With the Pentax 18-55mm lens, the K-r captured an average sized macro area (for an SLR kit lens), measuring 2.54 x 1.68 inches (64 x 43 millimeters). Details were soft in the center of the frame, and softer in the corners. (Most lenses have some softening in the corners at macro distances.) The Pentax K-r's built-in flash throttled-down well for our standard macro shot in auto mode, producing a very good exposure with no detectable shadow from the lens.
Slightly above average distortion at wide-angle, about average at telephoto with the 18-55mm lens.
|Barrel distortion at 18mm is 0.9 percent|
|Pincushion distortion at 55mm is 0.2 percent|
The Pentax 18-55mm lens produced about 0.9 percent barrel distortion at wide-angle, which is slightly above average and noticeable in some of its images. At the telephoto end, there was about 0.2% pincushion distortion which about average, but still 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).
The Pentax K-r offers optional Distortion Correction when using DA, DA L, and DFA lenses, as well as several of the company's FA Limited lenses.
|Distortion Correction On: Barrel distortion at 18mm is <0.2 percent|
|Distortion Correction On: Barrel distortion at 18mm is <0.1 percent|
The Pentax K-r does not apply any geometric distortion correction to JPEGs by default. As mentioned previously, 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 with Distortion Correction disabled and enabled. As you can see, the 0.9% barrel distortion in the uncorrected wide-angle shot has been reduced to less than 0.2%. The pincushion distortion at telephoto has been over-corrected just slightly to less than 0.1% barrel distortion.
Chromatic Aberration and Corner Sharpness
Moderately high levels of chromatic aberration from the 18-55mm lens at wide-angle, though much lower CA at full telephoto. Strong blurring in the corners at telephoto and somewhat soft through-out the frame at both wide-angle and telephoto.
|[email protected]/3.5: Upper right
C.A.: Moderately high
Softness: Slightly soft
|[email protected]/3.5: Center
C.A.: Very low
Softness: Slightly soft
|[email protected]/5.6: Upper right
C.A.: Moderately low
Softness: Very soft
|[email protected]/5.6: Center
C.A.: Very low
Softness: Slightly soft
Chromatic Aberration. Chromatic aberration is moderately high and quite bright at the full wide-angle setting of the Pentax 18-55mm kit lens. At full telephoto, chromatic aberration is lower and not as 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-r does not apply any chromatic aberration correction to JPEGs by default, as uncorrected RAW files have similar amounts. As mentioned previously, there is however a menu option to turn Lateral Chromatic Aberration Adjustment on (see below).
Corner Sharpness. The Pentax 18-55mm lens produced slightly soft corners at wide-angle, though the center was also slightly soft. The bottom right corner was the sharpest with the other three showing very similar softening. Some vignetting (corner shading) is also noticeable at wide-angle. At full telephoto, the top-right corner was the softest with blurring extending well into the frame. The other three corners were slightly soft, as was the center.
Chromatic Aberration Reduction
The Pentax K-r offers optional lateral chromatic aberration reduction for the same lenses that are supported for distortion correction.
|Camera JPEGs, Lateral Chromatic Aberration Reduction|
|[email protected]/3.5: Disabled||[email protected]/3.5: Enabled|
As illustrated in the crops above, the Pentax K-r was removed much of color fringing from the 18-55mm kit lens with Lateral Chromatic Aberration Adjustment enabled, though it still leaves some visible chromatic aberration behind, especially along diagonal edges.
Overall, this is just an average performance even for an inexpensive kit lens. If you're interested in purchasing the Pentax K-r with the kit lens, make sure to buy from a retailer that allows hassle-free returns and test the lens thoroughly within the exchange period.
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Pentax K-r Photo Gallery .