Sony SLT Alpha A55 In-depth Review
The SLT-A55's translucent mirror design and full-time live view make it easier to implement a video mode than it would be on a 'traditional' DSLR, which needs to flip its mirror out of the way before it can start recording. It also means that the A55 can use its phase-detect AF sensor where 'traditional' SLRs and interchangeable lens cameras have to make do with the slower contrast detect systems. The SLT-A55 is Sony's first SLR (and, after the NEX-series, its second large sensor camera) to come with a movie recording function.
The camera offers 1080i video in AVCHD format (which offers excellent quality with efficient compression and is most suitable for viewing on a HD television set) or 1440 x 1080 pixels in the less efficient but more readily sharable MPEG-4 format. Despite the pixel count the MP4 video is still captured in the 16:9 aspect ratio and is usually interpolated up to 1920x1080 when played back so doesn't appear stretched or squashed.
The camera can record for up to 29 minutes (around 9 minutes if SteadyShot is turned on, depending on the ambient temperature). MP4 video, due to the constraints of memory card file systems, can only record files up to 2GB in size while the AVCHD system can split videos across multiple files to circumvent this limit.
In AVCHD mode the A55 offers high quality HD video capture at 1920 x 1080 pixels (1080p) at 25/30 frames per second (depending on whether your camera is a PAL or NTSC model), though the files are doubled up to 1080 i at 50/60 fps for HDTV compatibility. If you record your videos in MPEG-4 format you can also choose a smaller VGA video size.
The built-in microphone captures stereo audio but you can also connect an optional external stereo microphone to provide greater directionality and isolation from lens noise. There is a small built-in speaker for video playback in-camera.
1920 x 1080, 1080i (60/50fps), Av. 17Mbps
1440 x 1080, 1080p (30/25fps), Av. 12Mbps
640 x 480 (30/25fps)
|Audio||• Dolby Digital Audio
• Stereo audio capture via optional external mic.
|Format||AVCHD / MPEG4|
|File size||2.43 MB/sec (1080i AVCHD), 1.65 MB/sec (1440 x 1080 MPEG4))|
|Max file size per clip||2.0 GB for Motion JPEG, card capacity for AVCHD (new file is created automatically after file size has reached 2 2.0 GB)|
|Recordable time||Approx 29 minutes (around 9 min with SteadyShot enabled)|
Using Movie Mode
Capturing a movie on the Sony SLT-A55 is easy. Just press the red movie button to start and stop recording. The A55's movie mode lacks manual control over shutter speed and aperture (if you shoot with manual focus you can set the aperture before you start recording) but nevertheless still offers some scope for creative control. You can apply exposure compensation while creative styles, white balance, AF area and metering mode are all taken over from the current stills image settings. In the menu there are only three movie options to be found - you can select the recording format and size and deactivate audio recording.
The autofocus is set to continuous but of course you can focus manually if you wish. If in 'Local' AF mode you can change the AF area while shooting. Due to having its phase-detect AF available at all times, the A55 focuses faster than other DSLRs. But, because of the shallow depth-of-field offered by large sensor cameras (and depending on the subject) shooting video with AF might not be entirely advisable. Firstly the camera doesn't always focus on the subject you want it to focus on which can lead to visually unpleasant 'focus jumps' and secondly the noise of the focus motor can be heard on the audio track. Although the latter can be avoided by using an external microphone, due to the narrow depth-of-field of an APS-C sensor camera such as the Sony SLT-A55, even small shifts in focus will be much more visible than on small-sensor camcorders or compact cameras.
Movie mode displays
|There are only three movie options in the menu: you can set movie format and size and switch audio recording off.||The movie screens look much like the regular shooting modes but are using the entire 16:9 aspect ratio of the screen.|
|There's an option with additional shooting information...||...and the digital level gauge.|
Video quality comments
The Sony SLT A55's sensor is APS-C size and therefore you can't quite create the same depth of field effects as on a full-frame-camera such as the Canon EOS 5D Mark II but you still get a much shallower, more cinematic depth of field (and much better image quality) than most camcorders or any digital compact camera. The videos are screen-filling and the level of detail and smoothness are pretty much in line with other cameras of this level. In low light the footage becomes grainy but again, this is not worse than on any of the competitors. There is also no discernible quality difference between the MPEG-4 and AVCHD formats.
Continuous is the default AF mode when shooting video (single is not available). It is generally pretty good but there are some occasional focus shifts and the AF can, despite the A55's translucent mirror, struggle to follow fast-moving subjects. As sometimes the focus motor can also be heard in the audio recording we would recommend switching the AF off and focus manually as an alternative.
Talking of audio, the A55 has built in stereo microphones but with the option to add better external stereo mics. We did not have a chance to test the latter but experience tells us that an external microphone a very useful accessory if you plan on recording 'serious' video with sound. The built-in mic is pretty sensitive and though the sound quality is perfectly acceptable it's not directional enough, and tends to pick up camera operation noises.
Like pretty much all other video-capable large-sensor cameras the SLT-A55 suffers from distortion caused by its rolling shutter. The readout of the sensor means horizontal lines of the image are scanned, one after another, rather than the whole scene being grabbed in one go. The upshot is that verticals can be skewed if the camera (or the subject) moves too fast - the top of the image has been recorded earlier than the bottom, so vertical lines can be rendered as diagonals. The effect is clearly noticeable on the A55 but you have to pan quickly to make it too intrusive. The camera is fairly average in this respect but we have seen a few models which handle the problem a little better.
Overall the A55's video mode delivers good quality output that is far better than anything you'd get from a digital compact camera. The optional external microphone is a good option for more serious videographers but the lack of control and shutter speed during video recording make it less of a creative tool than some competitors. Below you'll find some examples of videos taken with the camera for you to download and draw your own conclusions.
Caution: very large files
Sample video 1
|1920 x 1080, 50 fps, interlaced, AVCHD, .MTS file, 12 sec. 23.8 MB|
Sample video 2
|1440 x 1080, 25 fps, MPEG-4, .MP4 file, 9 sec. 13.9 MB|
Sample video 3
|1920 x 1080, 50 fps, interlaced, AVCHD, .MTS file, 7 sec. 12.3 MB|
Sample video 4
|1920 x 1080, 50 fps, interlaced, AVCHD, .MTS file, 6 sec. 11.2 MB|
Sample video 5
|1920 x 1080, 50 fps, interlaced, AVCHD, .MTS file, 12 sec. 21.7 MB|
Sample video 6
|1920 x 1080, 50 fps, interlaced, AVCHD, .MTS file, 5 sec. 9.1 MB|
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