Pentax K-7 Review

 
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Pentax K7 Video Recording

In many recent SLR announcements, video capabilities have dominated the "what's new" feature list. The Pentax K-7's video capability is no less newsworthy than those of competing models, but the plethora of other new features and improvements mean there's a lot to be excited about beyond video recording.

That said, the Pentax K7's video recording introduces some capabilities we've not seen in prior SLR models from competing manufacturers, and firmly establishes Pentax's credentials as a leading-edge purveyor of video-capable SLRs.

Pentax K-7 Video: Image Size, Frame Rate, and Encoding

New video capability. The Pentax K-7 offers 3 resolution levels for video recording, all at 30fps with stereo sound (when an external mic is used; the internal mic is monaural).

The Pentax K7's all-new CMOS sensor records video at a native resolution of 1,536 x 1,024 pixels, at a rate of 30 frames/second. The native 1,536 x 1,024 pixel resolution can be recorded directly (a 3:2 aspect ratio), or can be downsampled to produce 1,280 x 720 HD-resolution movies (a 16:9 aspect ratio), or 640x416 pixels standard-def movies (a 3:2 ratio again). All video modes record at 30 frames/second; there is no option for a lower frame rate, and the 30 fps at HD resolution is better than many competing models, several of which top out at 24 fps.

The Pentax K7 records its movies as motion-JPEG (AVI) files, rather than the AVCHD format favored by some manufacturers. AVCHD is much more conservative of memory card space, but at the cost of severe loss of image quality when a lot of the image changes from one frame to the next, as is the case when panning or in closely-cropped video of a rapidly-moving subject. AVCHD is a subset of the broader H.264 video compression spec, one that places fairly heavy constraints on the recorded bitrate (hence its smaller file sizes). Cameras with sufficient processing power can use H.264 encoding at higher bitrates to avoid some of the limitations of AVCHD, but this comes with the requirement of greater processing power, for both recording and playback.

As noted, the Pentax K-7's video suffers no compression-related quality loss during panning, but the consequence is very large file sizes: A minute of HD video can very easily produce a several hundred megabyte file, depending on subject matter.

Recording is only part of the story, though: Editing and playback are the other aspects to be considered. When it comes to editing, the Pentax K7's AVI format is much easier to deal with than H.264-encoded video (including AVCHD), at least currently: The more sophisticated encoding used in the H.264 standard requires quite a bit of processor power to pull it apart and put it back together again, so frame-accurate editing of H.264 requires a fast processor and capable editing program.

When it comes to playback, it's perhaps a bit of a toss-up between the two formats: AVI plays back much better on computers with relatively modest processors, while AVCHD files can be read directly by some television sets, and played back with better quality on HDTVs through the Pentax K7's HDMI port.

Here's a list showing what to expect for file sizes with the Pentax K-7's video recording:

Pentax K-7 Video Options
Motion JPEG Format (.AVI files)
Menu Designation
Resolution and
Frame Rate
Quality Level
File Size

1.6M

1,536 x 1,024
30 fps

High

270 - 350 MB/minute

Medium

270 - 340 MB/minute

Low

80 - 190 MB/minute

0.9M

1,280 x 720
30 fps
(720p HD)

High

320 - 390 MB/minute

Medium

53 - 195 MB/minute

Low

47 - 180 MB/minute

0.3M

640 x 416
30 fps

High

57 - 110 MB/minute

Medium

29 - 58 MB/minute

Low

29 - 58 MB/minute

(Measurements were made with a hard-to-compress digital noise image, and a blank white screen, to show the extremes in terms of high and low bitrate, respectively.)

The results of our tests of the K-7's frame size and compression levels were pretty interesting. We only found a significant difference between the Medium and Low quality settings at the largest frame size: At the two smaller sizes, the medium and low quality settings produced almost identical file sizes. It was also very interesting to note that the file sizes for the middle frame size ("0.9M" on the camera menu; 1,280x720 pixels, or 720p in HDTV terms) at the highest quality level were actually larger than those we found with the largest frame size.

The file-size results correspond to what we found in the K-7's video files: The best image quality seemed to be in its 0.9M (720p) mode, at the highest quality setting. Its largest video format showed noticeably more JPEG artifacts, even at the highest quality setting. With all frame sizes, we felt that recording at anything less than the highest quality setting produced too many JPEG artifacts for our tastes: Smaller file sizes are good, but only if they provide the image quality we're looking for.

Here are some examples of video from the Pentax K-7, showing typical results under daylight conditions. (Stay tuned, we hope to add more videos later.)

Pentax K-7 Video Samples

1.6M Highest Quality:
1,536 x 1,024, 30fps

(71.6 MB)
(Image Stabilization Enabled)
0.9M Lowest Quality:
1,280 x 720, 30fps

(47.7 MB)
0.3M Highest Quality:
640 x 416, 30fps

(24.6 MB)



Pentax K-7 Video-Mode Focusing

When we first saw a K-7 prototype prior to its announcement, were excited to see that it supported contrast-detect autofocus during movie recording. Unfortunately, this feature didn't make it into final production models. The prototype contrast-detect AF cycle was rather slow, visible in the video, and quite audible via the built-in microphone with most lenses, but we would have welcomed it in production models all the same: The audio issue could have been solved by using an external mic (like the excellent Rode SVM, mentioned below), and for some subjects, the contrast-detect "hunting" might have been acceptable.

As it is, focusing in movie mode with the Pentax K-7 is much the same as it is with most other video-capable DSLRs: You can trigger a contrast-detect AF cycle prior to the beginning of a recording by hitting the AF button on the camera's rear panel, but there's no autofocus during recording. You can manually focus the lens during a recording, though, and the true manual operation of AF on Pentax's lenses means you can do this more or less silently, simply by being careful about turning the focus ring. (We recently tested the Olympus E-P1, which uses "fly by wire" focusing, whereby the focus ring only instructs the camera to move the lens elements rather than moving them directly via a mechanical coupling. This meant that small clicks could be heard on the audio track every time the E-P1 changed the focus setting, regardless of how slowly we turned the focus ring. With true manual operation of its lenses, the Pentax K-7 doesn't have this problem.) As is the case in Live View mode, pressing the Info button on the camera's rear panel lets you zoom in up to 6x to assist with manual focusing, but note that this is only possible before recording has started: Once the camera has begun recording, only the normal 1:1 view is available.

As we've noted in other SLR reviews, the good news with focusing for video is that you can get surprisingly good depth of field in video mode by stopping the lens down, thanks to the relatively low resolution of the video image. With a pixel resolution of only 1.6 megapixels in the Pentax K-7's highest-resolution mode or 0.9 megapixels in 720p HD mode, images that would be unacceptably blurred as 15 megapixel still shots look perfectly fine as video frames. This not only provides greater depth of field at any given aperture, but is also more forgiving of diffraction limiting at very small lens apertures. Diffraction at small apertures means you'd usually want to avoid f/16 or f/22 for still images, but again, the results generally look perfectly fine at video resolutions. Bottom line, with the K-7's lens set to f/16 or f/22 (assuming you're shooting under fairly bright conditions), you'll be surprised by how little focus adjustment is needed during a typical video recording.

Pentax K-7 Video Exposure Control

True aperture control with video! This was big news when the K-7 was announced. Since then, Canon has announced a firmware update for their 5D Mark II, which now also supports manual aperture control. And, while not strictly SLRs, the Panasonic GH1 and Olympus E-P1 both also provide aperture-priority video recording.

Many video-capable SLRs only offer automatic exposure in their movie modes, but the Pentax K-7 gives you a choice of either automatic or aperture-priority exposure mode. In Auto aperture mode, the camera adjusts the aperture as needed, but doesn't report the current value on the LCD screen. (We'd like to see a future firmware update add aperture display.) In manual aperture mode, the current aperture is displayed in the lower left corner of the LCD screen, and can be changed by rotating the rear command dial. This is a great feature that's as yet available on only a few video-capable interchangeable-lens cameras. The ability to control depth of field is very nice, giving you that much more creative control over your videos.

In common with most other video-capable SLRs, the Pentax K-7 offers the full range of white balance settings in movie mode, including four different options for fluorescent lighting, and Kelvin values ranging from 2,500 to 10,000. You can also select any of the K-7's Custom Image modes, including Bright, Natural, Default, Portrait, Landscape, Vibrant, Muted, and Monochrome. As with still-image shooting, settings for saturation, hue, high/low key adjustment and contrast can be adjusted independently for each mode. A sharpness setting is available as well, which we were slightly surprised to find actually did affect the sharpness of the video images, to a very noticeable degree. (Note that turning the sharpness up too high will make the JPEG compression artifacts much more evident, though.) All in all, the K-7 really seems to lead the field in the amount of control it gives you over the color and tonality of its video imagery.

One movie-mode exposure parameter that the Pentax K-7 unfortunately doesn't let you control is its shutter speed. The shutter speed appears to be tied to its frame rate, and regardless of the light level involved, rapid motion is always blurred to about the level you'd expect with a 1/30 second exposure time. (As noted above, the video frame rate of the K-7 is 30fps in all resolution modes.) Shutter speed control is currently very rare in video-capable interchangeable-lens cameras: As of this writing, only the Canon 5D Mark II and Panasonic GH1 offer this feature. While you can control the lens aperture on some competing SLRs by faking-out the exposure system, the Pentax K7 is the first video-capable SLR that we're aware of that lets you set the lens aperture explicitly. You can't adjust it during recording, but whatever value you set before you begin your clip is the one the camera will use. This is a great feature, one that's been sorely lacking in other video-capable SLRs. We really liked the control this gave us over the depth of field of our recorded videos, and liked knowing that the aperture was exactly what we'd set it to, not some value we hoped we'd tricked the camera into using.

Pentax K7 Video: Image Stabilization

The Pentax K-7's body-based image stabilization can be used when recording movies. Not only does this make any lens you're recording with into an IS model, but we found that the image stabilization worked exceptionally well when recording videos. We've recorded videos with other SLRs using IS lenses, but the level of stabilization we found in the Pentax K7 seemed better than what we'd seen previously. Because the Pentax K-7's IS system provides such a high degree of stabilization, there's a bit of a "floating" feeling when recording videos with IS enabled: As you move and pan the camera, the video image tends to lag a little behind your motions, "catching up" when you come to a rest. A related IS effect is that the subject can drift up or down or from side to side slightly during recording. This can be slightly disconcerting, but the upside is that your videos will be much more stable than otherwise, even holding the camera at arm's length, or when shooting with a long telephoto lens. As noted immediately below, the issue with IS noise in the audio track that we observed in the prototype samples appears to have been eliminated in production models, for all but fairly extreme camera movements.

Pentax K-7 Video: Audio recording

External Mic. This Rode SVM external stereo mic works wonderfully with the Pentax K-7: Audio is super-crisp, stereo separation is great, and it picks up no noise or vibration from the camera body thanks to its rubber suspension system.

Like most competing SLRs with video recording capability, the Pentax K7 sports an internal microphone that can record an audio track. Internal mics are somewhat problematic, though, in that they're prone to picking up noise produced by moving your hands on the camera or actuating any controls while recording. In the case of the Pentax K-7, the issue can be exacerbated if you choose to use the body-based image stabilization system during movie recording. A prototype problem with the IS system affecting the audio track now appears to have been largely corrected: With our production sample, you can hear the IS in the audio track if the camera is jostled a good bit during recording, but not when it's being held relatively steadily: The light clacking sound we hear on the audio track in the face of significant camera movement seems to be the result of the sensor unit bumping up against its stops. If the camera is held even reasonably carefully, we were hard-pressed to hear any IS-related noise at all, even in a quiet office environment. In normal usage, you thus shouldn't hear any noise from the IS system, unless you're panning quite a bit, or if unstable footing results in a lot of camera movement. Here's an example (29.9MB) of audio recorded in a quiet office environment, with IS enabled.

We did find that the Pentax K-7's built-in mic does a good job of picking up ambient sound, with good sound quality and sensitivity. At the same time, it seemed to be less sensitive to sounds picked up from focus adjustment or hand movement on the body than some other cameras we've tested.

In a big bonus for serious video users, the Pentax K-7 sports a microphone jack on its left side, to which you can attach an external stereo microphone. As of this writing, relatively few video-capable SLRs offer options for external audio input. Pentax provided a Rode SVM shoe-mounted stereo mic for us to use with the K-7, and we found it to be an excellent addition. It's far from bargain priced, selling for around US$250, and does add noticeably to the bulk of the K-7, but its compliant mounting system pretty much eliminates any transmission of sound from the camera's body to the mic, and recorded sound quality was really excellent, with surprisingly good stereo separation: Listening to videos recorded with it, the sound was remarkably crisp, and we could very clearly locate sound sources spatially. If you plan to use the Pentax K-7 for any serious video recording, we strongly suggest that you invest in an external mic like the Rode SVM.

Pentax K-7 Movie Recording User Interface

The Pentax K-7's movie mode is accessed via a separate position on the camera's mode dial, rather than being initiated from within still-picture Live View mode. There's no separate control button to start/stop movie recording: Pressing the shutter button begins recording, pressing it again stops it. Some SLRs have a dedicated button to start/stop movie recording, but we find the K-7's use of the shutter button more intuitive.

Our feelings about having a separate mode for video capture depend somewhat on the rest of the camera's user interface. On some cameras, combining video capture with normal still-capture mode would increase menu complexity too much, but that wouldn't be an issue with the K-7, given its menu layout. Providing video direct from Live View mode would require the addition of one more button to the rear of the camera to control video recording, though, and the K-7's tight control layout leaves little or no room for that. Bottom line, we agree with the engineer's decision to make movie recording a separate mode-dial option on the K-7.

Setting adjustments in movie mode are made via screen 3 of the Record Menu, where the Movie option leads to a whole sub-menu. We found this a little awkward when making frequent adjustments to video settings, as the extra level of menu selection meant more button-pressing to make the changes than would have been required if they'd been available from the main shooting screen via a "quick menu," as some cameras have. That said, the more commonly accessed options for white balance and Custom Image settings were easily accessible via the 4-way control buttons on the camera's back panel.

The Pentax K-7's Record Menu options for video recording are:


Pentax K-7 Record Mode Menu Movie Options
Top-Level
Selection
Second-Level
Notes
Recorded Pixels
- 1.6M [3:2] (1,536 x 1,204)
- 0.9M [16:9] (1,280 x 720)
- 0.3M [3:2] (640 x 414)
All modes record at 30fps

0.9M mode is compatible with display on an HDTV
Quality Level
- *** (high)
- ** (medium)
- * (low)
Per our image quality analysis below, we found only the highest quality setting worth using
Sound
- On
- Off
Movie Aperture Control
- Auto
- Fixed
"Fixed" lets you set aperture via the rear-panel control dial
Shake Reduction
- On
- Off



Pentax K-7 Video Quality and Artifacts

Relative to the video from other cameras we've tested, we found the Pentax K-7's video to be a bit sharper than average, and relatively free of motion-induced compression artifacts, but we also saw more JPEG artifacts in the video than we've come to expect. Here are some examples of what we found in the K-7's movie files::

Pentax K-7 Video Quality Samples
1.6M Mode, High Quality 1.6M Mode, Low Quality
We didn't find the K-7's highest-resolution video mode terribly useful. It's not a format that conforms to the HDTV spec, and even in its highest-quality mode (lowest compression), JPEG artifacts are clearly visible when played back on a computer. When the video is playing back, these appear as a distracting flickering in the image. They're obvious here in Marti's face in this frame-grab, but are less so with moving subjects during playback. Nonetheless, they can be quite distracting in static background objects, drawing attention away from your primary subject.
At the lowest quality setting, the 1.6M-mode video is all but unusable. The JPEG artifacts obliterate a lot of subject detail, and the flickering makes the video all but unusable. We didn't shoot a sample of 1.6M medium-quality video, but given that we didn't like the JPEG artifacts at the high-quality setting, we didn't think it was worth the time to check the medium-quality option.
0.9M Mode, High Quality 0.9M Mode, Low Quality
In the K-7's "0.9M" mode (720p resolution in HDTV parlance), the situation is much better. We can still see a few JPEG artifacts at the high-quality setting, but they're relatively minor, and we didn't find them distracting during movie playback. The resulting files are quite large, but the video is pretty good quality, and shows no motion-induced compression artifacts (see below).

On a positive note, the K-7's video is noticeably more crisp than that of most SLRs we've tested to date, particularly in 720p mode.

While nowhere near as bad as in 1.6M mode, we still found the JPEG artifacts a little distracting when we dropped to the low-quality setting at 0.9M resolution. (And, as noted above, there's essentially no difference between Medium and Low quality for 0.9M movie files.) Bite the bullet, buy a big memory card and huge hard drive for use with the K-7, and you'll be happy.
0.3M Mode, High Quality 0.3M Mode, Low Quality
We were a little surprised to see JPEG artifacts increase again at the lowest video resolution, even at the highest quality setting. Not too distracting, but we wish there were fewer, even at the cost of larger file sizes again.
As before, the low quality setting for 0.3M videos really wasn't usable due to distracting artifacts. As with the 0.9M mode, there again doesn't seem to be any particular advantage to choosing the medium quality setting, as it compresses the files about as much as does the low quality option.
0.9M Mode: No Motion-Induced Compression Artifacts
As we've mentioned before, we think that the larger file sizes are a worthwhile trade-off in avoiding the motion-induced compression artifacts of the AVCHD format. Here, there's quite a bit of blurring because I'm panning so rapidly, and the K-7's shutter speed is tied to the video frame rate. It's just normal motion blur, though, with no compression artifacts from the rapid panning and subject motion.
Here's good proof that the blurring in the shot at left is purely a function of the panning and subject movement. In this shot, I'm still panning rapidly (so there's lots of change in the image from frame to frame), but Charlotte's floating along between strides, and my panning is tracking her pretty accurately. As a result, she and the Frisbee are pretty sharp, with good detail.


Rolling Shutter Artifacts

Essentially every video capable DSLR currently on the market exhibits motion-related distortions called rolling shutter artifacts. These are caused because the image data is captured and then read off the chip sequentially by rows, rather being captured all at once. In the case of the Pentax K-7, with its 30fps frame rate, this means that image data for the last row of a given frame is captured and read out about 1/30 second after the data for the top row was captured. The effect on moving objects is similar to that of a focal plane shutter in an SLR, but more pronounced, because the video frame is read out much more slowly than the slit of a focal plane shutter moves across the sensor.

For a camera that scans video frames vertically (as all do that we're aware of), rolling shutter artifacts will be most noticeable for subjects that are moving rapidly side to side, or when the camera itself is being panned horizontally. Verticals in the scene will appear tilted to the right or left, depending on the direction of camera motion. As an example, consider the case of a camera being panned from left to right, with a flagpole or other vertical object in the middle of the scene when recording for a particular frame begins: If the top of the object was centered horizontally when the first line of the video frame is acquired, by the time the last line of the frame has been captured, the bottom of the object will have shifted to somewhere left of center: As a result, the vertical object would appear to be leaning to the right.

The shots below show some screen grabs from our evaluation of the Pentax K-7's rolling shutter behavior.

Pentax K-7 Video - Rolling Shutter Artifact
Reference: Static shot
This first shot shows what the subject looks like with the camera held steady. (Anything that's off vertical here is the result of faulty camera-holding technique. :-)
Rolling Shutter, 1.6M resolution
This shows the rolling shutter artifact (note the slanted verticals) about as bad as we could make it, without using absurd amounts of camera jiggling. (Note that the K-7's IS system was disabled for all these shots.)
Rolling Shutter, 0.9M resolution
The K-7 showed essentially the same amount of artifacting at its lower resolution settings as it did at its highest resolution one.
Rolling Shutter, 0.3M resolution
During playback, we found the rolling shutter artifact less visually obtrusive at lower resolutions, but close inspection of the video stream showed that that was simply a psychological effect of the lower-res images appearing smaller on-screen.

The visual impact of rolling shutter artifacts on the Pentax K-7 seemed greater than those associated with some other 30fps video modes we've seen recently (specifically, those of the Olympus E-P1 when shooting with its IS system disabled), leading us to wonder whether some cameras actually capture and transfer each frame of video somewhat faster than the frame rate itself would indicate. (That is, while some cameras might have a 30fps frame rate, each frame might actually be acquired and read out in less than 1/30 second.) Whatever the case, while this isn't a scientific test, we felt that the K-7's movies were somewhat more subject to rolling shutter artifacts than those from some other 30fps video systems we've seen.

The upside for the K-7 relative to rolling shutter artifacts is its excellent IS system. While you can avoid the worst effects of a rolling shutter by panning slowly, even minor jiggling of the camera due to hand-holding can produce a jelly-like appearance in the video output from some models. The K-7's IS system stabilized the video well enough that we experienced no such effects when the camera wasn't being panned. If our shooting required both stationary shots and rapid panning in the same segment, though, we had to shoot with the IS system disabled to avoid clacking noise in the audio track from the internal mic. With an external mic, this was much less of an issue.
(Unfortunately, if your shooting for any given segment will involve both panning and steady camera positions, you'll generally need to shoot with the IS system disabled, to avoid clacking on the audio track and somewhat erratic framing in response to rapid camera movements.)

Computer Requirements for Viewing HD Video

A typical computer these days has little trouble dealing with still images, but high-definition video can be another matter. Depending on the file format involved, it can take a pretty beefy computer to handle HD-resolution video playback without stuttering or dropping frames. The Motion JPEG image compression used by the Pentax K-7 is one of the less compute-intensive formats, though, and its 1,280 x 720 resolution means there's a good bit less data in each frame to deal with than in videos with 1,920 x 1,080 (1080i) resolution. The net result is that you should have no problem playing video files from the K-7 on your computer, as long as it's a relatively recent and reasonably powerful model. We don't have a specific benchmark for this, but if your computer is less than 3 years or so old, it should have no problem with the K-7's video streams. (By contrast, to play AVCHD or other keyframe-encoded video formats at full 1,920 x 1,080 resolution can demand a very powerful CPU and video card, to keep up.)

That said, the Pentax K-7's video codec doesn't appear to be terribly efficient, as it produces very large file sizes at its best quality setting. (And as noted earlier, its lower quality settings introduce an unacceptable level of JPEG artifacts into the image stream, so you'll want to use the highest quality setting almost exclusively.) So, while you might be able to play its videos on an older computer, you'll almost certainly need to increase your hard drive capacity. With video files occupying 330 MB/minute, it's a good thing that terabyte hard drives are so cheap these days. (At that pace, a terabyte hard drive could hold about 50 hours of video footage. That's a lot of footage if you primarily use the K-7 for casual "video snapshots," but if you're a serious video user, it can still go by pretty quickly.)

Pentax K-7 Video Mode: The Bottom Line

Overall, the Pentax K-7's video mode is a mixture of strengths and weaknesses. On the positive side, the K-7's video imagery was noticeably more crisp-looking than that of most SLRs we've tested to date. The downside is that its JPEG compression isn't as good as that of some other cameras, producing larger file sizes with more visible JPEG artifacts than we'd like. Its rolling shutter artifacts were a bit more obtrusive than those of 30fps video modes in some competing models, but less problematic than those seen in cameras shooting at only 20 or 24 frames/second. We were excited to see live contrast-detect focusing during movie recording on the prototype samples, but that feature didn't make it into the final production version, so the K-7 runs with the pack in that regard. We found the K-7's body-based IS provided excellent stabilization during video recording, with very little impact on the audio recorded by the in-body microphone, but the strong IS also produced a "floating" feeling in videos, and sometimes made it hard to keep the subject completely stationary within the frame. A big plus for serious users is the K-7's audio input jack, which lets you connect an external stereo mic. While the built-in mic turned in a workmanlike performance, the K-7's sound quality can be superb with a high-quality external microphone.

Video in SLRs is still somewhat at the bleeding edge of technology, so no camera we've seen (yet) does it perfectly. For the average user, though, the K-7's video is certainly good enough to avoid having to lug along a digicam on trips, just for the sake of capturing video snapshots. Recording in its highest quality setting at 720p resolution, its output will be acceptable for many more serious users as well.

 

Pentax K-7

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