Sony DSLR-A580 Video

Sony A580 Video Recording

Over the last couple of years, high-definition video capture has become a fairly common feature for interchangeable-lens cameras, available in many single-lens reflex and single-lens direct view cameras at all price points. The various implementations to date have spanned the gamut from models that keep control entirely in the camera's own domain, to those which offer significant creative possibilities, and here the Sony A580 falls in the middle ground. Some manual control is possible: metering mode, white balance mode, and creative style can all be defined prior to movie recording, and exposure compensation and lock are available at all times. As well as a stereo internal microphone, connectivity is available for an external microphone. The A580 doesn't offer full manual control, however, and nor is autofocus possible during video capture. As in many DSLRs to date, you're instead restricted solely to pulling focus manually during video capture, a notoriously difficult skill to master.

Let's look at the Sony A580's video capabilities in a bit more detail:

Sony A580 Basic Video Specs

• 1080i (1,920 x 1,080), 59.94i (interlaced) fields/second, 17 Mbps HD recording (50i in European versions) in AVCHD format (MPEG-4 AVC / H.264 w/ Dolby Digital audio)
• HDV 1080i (1,440 x 1,080 rectangular pixels), 29.97 fps, 12 Mbps, HD recording (25 fps in European versions) in MPEG-4 format
• VGA (640 x 480), 29.97 fps, 3Mbps standard-definition recording (25 fps in European versions) in MPEG-4 format
• Maximum clip length is 2GB or 29 minutes
• Automatic exposure only, but aperture adjustment possible before movie capture
• Manual focus only during video capture
• Exposure compensation available both before and during movie capture
• SteadyShot image stabilization, white balance, creative style, and metering mode can be set before movie capture begins
• Maximum clip length is slashed to just 14 minutes, if SteadyShot is enabled
• Stereo audio recording via built-in microphones or via a standard 3.5mm external mic jack
• Audio recording can be disabled altogether
• Video is cropped slightly from sensor data, with optional crop marks available in Focus Check live view mode only
  
  

Sony A580 Video: Image Size, Frame Rate, and Encoding

The Sony A580 records at three different video resolutions, and can record high-definition movies in either AVCHD or MPEG-4 formats. Audio is encoded during movie recording in Dolby Digital (AC-3) for AVCHD and AAC-LC for MPEG-4. No spec is provided for the sampling rate of the audio tracks, though video players report 48 kHz at 256 kbps for AVCHD and 48 kHz at 128 kbps for MPEG-4.

The table below shows the specs for various video recording options.

As noted above, the Sony A580 offers two video recording formats, either the HD-only AVCHD format or the less space-efficient but more computer-friendly MPEG-4. The MPEG-4 file format is a bit less efficient in its use of memory card space for a given image quality level, but is more widely supported, and seems to be a bit easier for older computers to read. AVCHD is the best choice if your primary output is going to be directly to a HD television, but MPEG-4 probably a better choice for your computer, particularly if it's more than a year or two old.

In AVCHD mode, the pixel resolution is 1,920 x 1,080, and the data stream on our test sample seemed to be recorded at an average rate of 2.1 MB/second, the maximum rate according to the "Main Profile" spec for AVCHD. No options are offered for lower bit rates, but in our experience, there wouldn't be much point to them: We've generally found lower AVCHD bit rates to result in poor detail and excessive artifacts, especially in higher-resolution and higher frame-rate cameras. At ~17 Mbits/second, file sizes are modest enough that we see little or no benefit in greater compression. (You'll definitely want to buy a really big memory card for use with your A580, though: Even with AVCHD compression, video files take up a lot of card space.)

With a frame rate of 60 fields-per-second (interlaced), the Sony A580 produces smooth motion, though not as smooth as could be possible with a sensor running natively at 60i. The A580's sensor is read at 30 frames-per-second (progressive) and video is interlaced to 60i by extracting alternate field pairs of each 30p frame. (The AVCHD standard does not define 1,920 x 1,080 at 30p, so providing 60i from a 30p sensor makes perfect sense.) While this is not true 60i from the sensor, it does have the advantage of making de-interlacing much easier, though sophisticated de-interlacers can certainly produce more fluid looking motion from true 60i video.

MPEG-4 mode offers a choice of two resolutions both recorded at 30 frames/second (progressive), with data rates and compression ratios as detailed in the table above. The MPEG-4 formats on the Sony A580 actually use slightly less memory card space than does its AVCHD format. This may in part be due to their lower frame rate, but also reflects the reduced resolution and significant compression that the A580 applies to these files.

Sony recommends use of a Memory Stick PRO Duo Mark 2, Memory Stick PRO-HG Duo, or SD / SDHC / SDXC Class 4 rated memory cards for movie recording, to ensure that card write speed isn't a limiting factor in clip length. (Slower cards will likely still work to some degree, but with a reduction in clip length, especially in AVCHD mode.)

Here are some examples of video shot with our sample of the Sony A580:

Sony A580 Video-Mode Focusing

Prior to recording, you can let the camera set focus either using phase detection if framing your subject through the optical viewfinder or in the standard live view mode (and with a brief interruption to the live view feed when in Focus Check LV mode), or using contrast detection (available only in Focus Check LV mode). Once video capture has started, though, autofocus is no longer available, and you're restricted solely to adjusting focus manually.

The lack of autofocus during movie recording with the Sony A580 is something that may give many potential owners pause, as focus is so critical in still photography, and dealing with moving subjects would seem to make it even more so. In practice, we were surprised to find it not nearly the issue we expected it to be. This may be because the lower resolution in video mode greatly increases the effective depth of field: Subjects that would be well out of focus when shot at the A580's maximum still-image resolution of 16 megapixels often looked just fine when viewed at even the maximum video resolution of 1,920 x 1,080. Lower resolutions only increase this effect. And it's not just the resolution, either, the video compression introduces quite a bit of softness on a frame-by-frame basis, further masking softness due to defocusing.

Still, the Sony A580's manual-only focusing in movie mode means that a whole new generation of non-professionals will now learn what it means to "pull focus" while recording movies, as the point of interest move from one subject to another, or if the subject moves significantly closer to or further from the camera during a segment. "Focus pulling" is a cinematic technique often performed by someone other than the camera operator, who is usually too busy framing the image to attend to focus as well. But millions of Sony A580 owners will be able to try a technique that few camcorder owners can.

In our own experience playing with the Sony A580 (and many other DSLRs which lack live video AF), we've found pulling focus during a recording to be a skill that requires some learning, particularly if there are things going on in the scene that need paying attention to. If we knew the approximate locations where the subject would be at the start and end of a clip (think of a video of a Little Leaguer sliding into home), we could check the corresponding positions of the focus ring and then try to repeat them while the action was taking place. This is a little hard to do with only a ring to grab onto, though, as the tactile reference for the different focus positions is pretty weak.

If you don't know in advance how the subject is going to move, you can try to judge focus from the image on the A580's rear-panel LCD and adjust accordingly. The high resolution and sharpness of the LCD makes this more practical than it might sound. Once again, some practice (and inherently good reflexes) are required, but given enough practice, it can work reasonably well.

Sony A580 Video Exposure Control

While the Sony A580 lets you record movies directly from any of its still-image exposure modes, including aperture-priority, shutter-priority, and full manual exposure modes, exposure is controlled automatically in all but aperture-priority mode, which allows semi-automatic control. Regardless of mode dial position, the camera always retains control of the shutter speed and ISO settings, as well as the aperture in any mode except aperture-priority. This is an important difference (and step upwards from) the Sony A560, however, as although the user manual states that aperture control is possible in aperture-priority mode for both cameras, we found during our testing this is actually only true for the A580. The less expensive A560 model simply ignored the selected aperture once recording began, and selected its own. The ability to stop down the aperture is particularly useful since you can only focus manually during video recording, as it provides a means to increase depth of field (and hence, the chance that your chosen subject is in focus), so it's a real bonus that the Sony A580 provides it.

Exposure compensation adjustments made in still-capture modes carry over into movie recording, provided that there's enough light. (That is, if it's too dark, boosting the EV adjustment won't make your video any brighter.) It's also possible to adjust exposure compensation during movie recording, unlike aperture adjustment. White balance settings also carry over to video mode, as do the metering modes and creative styles, but these can only be set prior to capture.

Shutter speed is one aspect of video exposure we've recently become more aware of. It turns out that slower shutter speeds tend to produce more natural-looking videos than faster ones: The motion blur associated with a slower shutter speed tends to smooth-out transitions between frames with rapidly-moving subjects: Cameras with 30fps recording, but shutter speeds 1/100 second or higher produce somewhat choppy, artificial-looking movie footage, while cameras with exposure curves biased toward shutter speeds in the 1/30 - 1/60 second range show a lot more motion blur, but the end result looks more natural to the eye. Unfortunately, there's no way to directly adjust shutter speed during movie recording on the A580, although you can to some extent influence it in your desired direction via the availability of aperture-priority mode.

Sony A580 Movie-Mode Image Stabilization

Sony is unique among camera manufacturers, in having both body-based and lens-based image stabilization technology in their product lines. In the case of the A580, image stabilization happens in the body, and so it is available with all lenses. Sony claims that the SteadyShot anti-shake system in the A580 provides a 2.5 to 4-stop reduction in the blurring produced by camera shake. Translating that into real-world shutter speeds, a two-stop improvement means that a shutter speed of 1/30 second would give you the same resistance to blur from camera shake that a speed of 1/120 would without anti-shake. A 4-stop improvement would mean you could shoot as slow as 1/8 second and get the same results (blur-wise) as when shooting at 1/120 second unaided. Even the lower end of the specified range of effectiveness means a pretty significant improvement in one's ability to hand-hold long exposures. Since the A580 uses sensor data to provide a live view feed on the LCD display during video capture, the effect of stabilization can be monitored. A SteadyShot scale on the right side of the viewfinder display further indicates the degree of stabilization.

One drawback of the Sony A580's in-body image stabilization is that, when enabled, it somewhat reduces maximum clip length, and pretty drastically so, unlike in its A560 sibling. The greater reduction in the A580 is likely an indication not only of heat created by operation of the sensor shift mechanism, but also from the sensor itself, leading to the temperature threshold being reached more rapidly. When disabled, the Sony A580 can record clips as long as 29 minutes at an ambient temperature of 68F (20C), presuming the file size limit of two gigabytes isn't reached first. With SteadyShot enabled, though, the clip length is reduced by half, to around 14 minutes -- a full ten minutes less than in the A560. Of course, if you frame your movie in the Focus Check LV mode before capture starts, you're already using the main image sensor and stabilization mechanism, and so this will further eat into your available capture time. That's important to note, because Focus Check LV mode is the only one that provides any indication of the crop that will be applied during movie capture, so you're presented with a choice of either being able to precisely frame the start of your movie, or of maximizing your clip length -- but not both.

Sony A580 Video: Audio recording

Like most competing SLR cameras with video recording capability, the Sony A580 features a built-in microphone, but it goes some of its competitors one better, in that this actually consists of two internal microphones, located on either side of the flash / electronic viewfinder housing, providing stereo sound. It also provides for recording via an external stereo microphone, courtesy of a standard 3.5mm jack located under a rubber flap on the left side of the camera body. Sony's only published spec for the A580's audio recording capability simply says "Dolby Digital / MPEG-4 AAC-LC", so we don't officially know the sampling rate or number of bits of A/D resolution employed, although third-party MPEG players suggest a 48 KHz sample rate.

As with with most video-capable SLR and compact system cameras we've tested, the A580's internal microphones are exquisitely sensitive to noise produced when operating the camera's controls or even moving your hands on the body. Since the A580 doesn't allow autofocus during video, and Alpha-mount lenses feature a direct mechanical coupling for manual focus, drive noise from AF motors isn't an issue, but moving your hands on the camera body or operating controls such as the focusing mode switch (to enable manual focus) or exposure compensation are likely to leave noticeable noises on the recorded audio track.

As with most video-capable interchangeable lens cameras, the Sony A580 doesn't have any provision for manual audio level control, whether working from the internal or optional external mic. Of course, this isn't likely to be an issue for the A580's primary target buyers.

Sony A580 Movie Recording/Playback User Interface

The Sony A580 makes movie recording very easy, as you can initiate it at any time, regardless of the mode-dial setting: Simply press the prominent Movie Record button with the red dot at its center on the camera's top panel, and the camera will start recording video. The only slight hiccup is that only a portion of the sensor data makes it into the final movie -- that is to say, the A580's movie is cropped somewhat from the total sensor area. If you're using the viewfinder to frame images, the area that will be cropped isn't indicated, and nor is it shown by default in live view mode. If you enable one of the three grid displays in Custom Menu screen 2, small framing marks will be shown along with your selected grid when in Focus Check live view mode, mitigating the issue, but potentially reducing your video clip length, since this mode operates off data from (and hence warms) the main image sensor. It's not possible to preview the crop area at all in standard live view mode. The cropping does also make truly wide-angle videography a little more difficult to achieve, although at the same time, it adds a slight boost at the telephoto end, where we'd wager it is likely of more use to many consumers anyway.

Normally, this is where we'd list the Movie-mode menu items, but the A580 has no separate movie menu. In fact, the only menu items exclusively related to video recording are the choice of file format (AVCHD or MPEG-4), the image size (1,920 x 1,080 for AVCHD; 1,440 x 1,080 or 640 x 480 for MPEG), and whether movies should be recorded with or without an audio track.

Playback mode on the Sony A580 is decidedly odd. The odd part is that the A580's playback is an either/or proposition, relative to stills and videos: If you've just shot a video and press the playback button, you'll see only movies that are stored on the card; not the still images. Likewise, if you've just shot a still image, you'll only see other stills when you hit the playback button. To switch between the two modes, you have three options -- either drop into thumbnail view and scroll over to the left, to select the correct tab on that screen, or visit the Playback menu and change the Still / Movie Select option, or simply grab a throwaway exposure of the type you want to view. We actually found it much more convenient to hit the Movie Record button twice (to record a brief video clip) than to navigate through the playback menu to change the playback mode. Sony introduced this playback mode in its NEX-series SLD cameras, where it caused us some consternation until we figured out what was going on. "Where'd all my movies/stills go?" RTM, as they say, but we can only imagine the dismay many users will experience (if only until they read the manual) when they think all their vacation photos disappeared after they'd finally shot a video. Since so few people actually do read manuals, we also suspect this is going to be the source of a lot of service calls to Sony's support centers.

The likely reason for this odd either/or choice for movie/still playback reveals itself when you try to scroll through movies you've recorded, to find a particular one you want to play back: Scrolling through recorded movies is just ineffably slow. Well, perhaps not ineffably; it's a matter of a couple of seconds per movie, but that's slow enough that navigating through more than two or three movies can be seriously painful. Why so slow? The camera is lightning-quick scrolling through still images, and doesn't it save a JPEG thumbnail of each movie, for just this purpose? This is another area in common with the NEX-series cameras that's going to produce a lot of frustration with users.

While it pales beside the slow playback scrolling, we missed one other playback option that's become increasingly common on both digicams and compact system cameras; namely the "trim" function. Whenever you record a short video clip, it's inevitable that you'll start earlier and keep recording longer than the action you're interested in. (If you don't do this, you're almost certainly going to miss action you're interested in.) While "padding" like this is important and necessary, we like to keep our videos concise by trimming away the extraneous material at the beginning or end of the clip after they're recorded. Many cameras support doing this in-camera these days, but the A580 does not. You could certainly import the video clips to your computer and do the trimming there, but that's awfully cumbersome. Far easier to simply trim and toss away the unwanted footage on the camera. (More grist for the mill, for the first firmware update to the A580... ;-)

Rolling Shutter Artifacts

Essentially every video capable digital SLR/SLD currently on the market exhibits some level of motion-related distortion called rolling shutter artifacts. These are caused because the image data is captured and then read off the chip sequentially by rows, rather than each frame's data being captured all at once. In the case of the Sony A580, this means that image data for the last row of a given frame is captured and read out anywhere from 1/25th to 1/60th second after the data for the top row was captured. The effect on moving objects is like 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.

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 Sony A580 supports both AVCHD and MPEG-4 recording formats, although its highest-resolution video is only available in AVCHD format, and lower resolutions only in MPEG-4. The AVCHD format is slightly more space-efficient on the memory card relative to its quality level, and displays well on HD television sets, but is less widely supported by computer playback and editing software. If most of your video playback will be on a computer, you may find MPEG-4 to be more to your liking. On the other hand, if your computer supports AVCHD fine, that would be the preferred format, given its space efficiency.