The Sony A580 and A560 models will be its first DSLRs to do video of any sort. It also has two Single Lens Translucent cameras (DSLRs without the reflex), which use a pericle mirror to deflect some light up to a fast phase-detection auto-focus sensor while still letting about 70% of the light through to the image sensor.
Sony Alpha A580 |
The fixed, semi-transparent mirror in the SLT A55 and SLT A33 (pictured top) means that they can use their faster, more accurate phase-detection AF sensor all the time, including video mode. HD DSLRs can only use phase-detection in stills mode (while the mirror is down), because the mirror has to be locked up for video, which requires switching to slower, less accurate contrast detection AF (which isn't even available during recording on some cameras and is so slow it is almost unusable on others).
Typical Sony A55 users |
As the SLT cameras don't have to retract the mirror to take stills, they can also be used at high frame rates for photography (up to ten frames per second on the A55), and the cameras are significantly smaller than DSLRs. Although less light gets through to the CMOS sensor, this reduction is only the equivalent of about half a stop.
Sony A33 makes a splash |
All four Sony cameras record 1080 50i/60i (25p/30p capture on the sensor), using AVCHD at only 17Mbps, which is daft. When even its Handycam camcorders can record AVCHD at 24Mbps, why is Sony crippling these cameras by limiting them to 17Mbps?
Even so, it looks as if they can record reasonable video – have a look at the ever-excellent DP Review in-depth review of the A55, which has unconverted files you can download – the sixth clip is a great example of the jello effect you can get with a rolling shutter.
Given that for a similar price you can buy Canon's EOS 550D, you'd be nuts to buy any of these Sony cameras if you want to shoot video; but as consumer stills cameras (or even prosumer in the case of the A580/A560), which also shoot home videos, they could be worth considering.
By David Fox
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