If you've suffered a missed photo opportunity due to the short time your digital SLR takes to get its mirror out of the way, then Sony reckons it has the answer. The mirror inside the new α33 and α55 digital cameras doesn't move out of the way at all, it's just semi-transparent and simply allows the light from the lens through to the CMOS sensor while also redirecting some to the camera's autofocus sensor. Whether shooting stills or high definition video, Sony says that its new technology allows for simultaneous image capture and fast, accurate autofocus.

Existing mirror-based digital SLR cameras are restricted to getting shots in focus during the interval between image capture. When the user presses the shutter release, the mirror has to be moved out of the way so that light passing through the lens can hit the sensor. The short delay experienced can mean the difference between bagging that stunning action shot or being left with a disappointing blur. In a novel approach to the issue, Sony has removed the mirror-raising mechanism altogether and in its place has installed something it's calling Translucent Mirror Technology.

What's it all about?

It's essentially a semi-transparent mirror that doesn't actually move out of the way while a frame is captured. Instead, the light passing through the lens is effectively split in two when it reaches the mirror, some being directed up to the autofocus sensor and the rest passing through to the CMOS image sensor. The immediate benefit to the user is said to be one of speed. Making it possible to focus at the same time an image is being captured, Sony says that its SLT-A33 model is capable of an impressive 7 frames per second (fps) continuous autofocus shooting in Continuous Priority AE mode, while the SLT-A55V raises the bar even further by achieving 10 fps.

The new mirror technology is also said to provide visual gains for the Live View and viewfinder too. Full-time Live View lets users see images as received on the sensor, via a 3-inch 921,600 resolution Xtra Fine, variable angle tilt LCD with TruBlack technology and 100 per cent coverage. The Tru-Finder eye-level electronic viewfinder with 1.15 million dot resolution also benefits from full coverage but also throws in live video preview for good measure. Both alpha cameras cater for continuous autofocus during video shooting and as well as recording to full 1080p high definition in motion JPEG format, there's also the option of AVCHD 1080i.

Low light and fast moving image capture

Sony claims that its high precision TTL 15-point phase detection autofocus system with 3 cross sensors should result in clear images of fast-moving objects being accurately tracked and captured. Assisting with image clarity is SteadyShot INSIDE image stabilization technology that is reported to offer up to four exposure steps of anti-shake correction when shooting handheld. There's also a sensitivity range of ISO100 to ISO12800 with an additional multi-frame noise reduction mode. The camera shoots six frames in this mode and then combines them into a single shot, which is said to result in effective sensitivity of up to ISO25600.

Other image enhancement options include an Auto HDR mode which takes three images at different exposures and then merges them into one enhanced image with rich shadow and highlight detail. There's 3D Sweep Panorama technology that creates a couple of images from each shot to enable panoramic photos to be viewed in three dimensions with a compatible viewer. And giving the Auto mode a boost is Auto+, capable of automatically recognizing various scenes and altering settings to suit and is said to result in "cleaner, more dynamic pictures and fewer missed shots."

Both models feature an Exmor APS HD CMOS Sensor - the SLT-A33 at 14.2 megapixels and the SLT-A55V at 16.2 – and image processing is undertaken by the BIONZ engine. They're both compatible with the range of over 30 A-mount interchangeable lenses, sport both HDMI-out and USB 2.0 connectivity and support the SDXC media card format. The SLT-A55V also has built-in GPS for automatic geo-tagging of images and video clips.

Pricing and availability

Sony's SLT-A33 will be available from September and will cost US$650 for the body only. A body and 18-55mm zoom lens kit will also be available for US$750. The SLT-A55V will land a month later at a cost of US$750 for the body and US$850 for the body and lens kit.

Sony has released a short promotional video that highlights many of the features of both cameras:

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