Pentax K-r Optics

Pentax K-r Optics

Lens Compatibility

The Pentax K-r features a Pentax K_AF2 bayonet lens mount which is also compatible with K_AF3, K_AF, and K_A mount lenses, and according to Pentax, is compatible with the company's entire series of K lenses. While not all functions will be available with every lens, particularly with older lenses without AF contacts, die-hard Pentax fans who already have a large collection of lenses will doubtless be pleased with the K-r's broad range of lenses. (The camera's Custom menu offers a handful of options for older lenses, such as allowing shutter release without the aperture ring in the 'A' position, and catch-in-focus shooting for manual focus lenses.) The latest DA and DA * lenses with ultrasonic SDM and DC motors, and FA zoom lenses with power zoom are also supported, although not necessarily with all functionality that was once offered in the company's film cameras. (Pentax discontinued its last power zoom lens models in 2004, and we don't have access to any with which to confirm operation ourselves.)

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.

Autofocus System

Phase Detection. Pentax has upgraded the K-r's autofocus system to its latest SAFOX IX-series module, a designation which has only previously been applied to the company's medium format 645D and K-r models. Compared to the previous-generation SAFOX VIII system used in the K-x, SAFOX IX has the same point count and arrangement, but with several important differences. There are a total of eleven points, of which all but two are cross-type, sensitive to both horizontal and vertical detail. The cross-type points are arranged in a three by three grid towards the center of the image frame, while on either side of this grid there's one linear sensor.

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.

Beyond the change of phase detection module, Pentax has made a couple of other important changes to autofocus in the K-r, which now allows photographers to select the priority for single and continuous focus modes. For single AF, K-r users can opt for either focus priority or shutter-release priority. Focus priority requires an AF lock before the shutter can fire, while release priority starts exposure immediately that the shutter button is fully depressed, even if an AF lock hasn't been achieved. In continuous AF mode, the options are focus priority, or frame rate priority. The former requires an AF lock for each individual frame in the burst, while the latter emphasizes frame rate for each shot in the burst, even if this means a lock can't be achieved for individual frames in the burst.

Live View AF. The Pentax K-r offers three autofocus modes during Live View: Face Detection, Contrast Detection and Phase Matching. Face Detection and Contrast Detection analyze data streaming off the CMOS imaging sensor, while Phase Matching uses the same autofocus module as when you're using the optical viewfinder. In Face Detection mode, the camera gives priority to detected faces. A yellow frame is placed around the main face, while white frames appear for other faces. Up to 16 faces can be detected. If no faces are present, contrast detection is used. Of course, manual focus is also available.

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.

Dedicated AF-Assist Lamp. Unlike the K-x, the Pentax K-r has a dedicated AF-assist light: a small, very bright green LED located just to the right of and below the shutter button, as you look at the front of the camera. Because of its close proximity to the lens barrel -- it's quite a bit closer than that in the prosumer K-5 and K-7 models, due to the smaller body -- quite a few larger lenses and those with wide lens hoods may block the light from reaching the subject. You can generally dispense with lens hoods for available-light photography to improve the situation, though, given that in situations where AF assist is needed, you're not likely to be dealing with lens flare. Long tele zooms might not work with it, but then the AF-assist lamp's light won't project far enough for telephoto subjects anyway.

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.

AF Adjustment. If we've discovered anything reviewing lenses on SLRgear.com, it's that lenses and bodies don't always match. Sometimes they focus in front of the subject, sometimes they focus behind the subject, and sometimes they'll nail the point of focus. Sometimes it's the lenses that are out of tune too, so adjusting just the camera's AF to work well with one lens won't solve the problem with another; indeed, that approach could make other lenses worse. Camera companies are acknowledging this, building in adjustments to compensate for front- and back-focusing problems, but most restrict this only to their prosumer or professional models. The Pentax K-r strikes a middle ground between the K-x (which offered no correction), and the prosumer K-5 / K-7 (which correct not only for the body itself, but for up to 20 individual lenses too). The Pentax K-r allows a general calibration for the body within a range of +/-10 arbitrary steps, but doesn't allow individual lens corrections, so the same value must be used for your entire stock, unless you have the patience to remember and manually reset the values every time you change the lens. Still, with most consumer and even some prosumer cameras not offering correction at all, anything is better than no correction capability at all.

Shake Reduction

Pentax has retained the K-x's in-body stabilization system unchanged for its follow-up camera. Unlike lens-based systems, the Pentax K-r's in-body stabilization functions with pretty much any lens that can be attached to the camera. Shake Reduction comes in very handy when shooting with long zooms without a tripod, as they magnify any blurring from camera shake during exposure. Shake Reduction is also useful when shooting under low lighting with a slightly slower shutter speed. According to Pentax, Shake Reduction gives you the flexibility of up to 4 stops slower shutter speed without risking blurring from camera movement; though realistically, exposures longer than 1/15 second typically turn out best with a tripod or other method of camera stabilization. Shake Reduction requires some communication from the lens, particularly the focal length setting. However, for lenses that cannot communicate with the Pentax K-r, you can set the focal length from 8 to 800mm through a setting in the Record menu.

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.

Dust Reduction

The Pentax K-r also includes a Pentax dust removal system, but it's the previous generation, rather than the updated DR II system that debuted in the Pentax K-7, and also features in the K-5. Like past models, the K-r relies on a combination of SP coating on the low-pass filter to keep dust from adhering to the sensor, and vibration using the sensor shift mechanism to try and remove dust from the sensor. Our past testing has found this to be rather ineffective, compared to systems like that in the K-5 which instead use a piezo-ceramic element to vibrate the low-pass filter. The Pentax K-r does at least offer a Dust Alert function which makes it easy to spot dust on the sensor by taking a test shot with optimal exposure and high contrast for detecting dust visually, making it easier to find and manually remove dust particles. The mirror can be locked up for this purpose in a Sensor Cleaning mode found in page four of the Setup menu.

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.

The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Pentax K-r Photo Gallery .