Digital Camera News

New Sony SLRs Use Translucent Mirrors

Sony has announced two new SLRs that offer a new approach: instead of moving the mirror up to shoot, the mirrors of the Alpha SLT-A55V and SLT-A33 are translucent, so the camera can shoot through it. This means, Sony claims, that they can shoot quicker and can focus while shooting stills and video.

Conventional SLRs include a mirror that reflects the light into the viewfinder for the user to see. When taking photos, this mirror flips up, allowing the light to pass through to the shutter and the sensor. This moving mirror means that most cameras can't focus while the mirror is up (as the focusing sensors are in the viewfinder), and that there is a slight delay between pressing the shutter button and the picture being taken while the mirror flips up.

The Alpha SLT-55

The new Sony Alpha SLT-A55V and SLT-A33 use a different approach: the mirror is translucent, letting some light through to the sensor and reflecting some up into the viewfinder, so both can be used simultaneously. When the user presses the shutter, the mirror remains in place. Sony claims that this different approach allows the SLT-A55V to shoot 10 frames a second while continuously focusing on the subject with the 15-point AF system. The new system (which Sony refers to as Translucent Mirror Technology) also allows the user to shoot video with the camera held to the eye, which provides a better preview than the screen when shooting in bright daylight. The cameras also use an electronic viewfinder, rather than the optical viewfinder offered by most SLRs. This viewfinder offers a 1.1x magnification; the user sees a little more around the edges than the captured images.

However, the downside of this system is that the mirror remaining in place while shooting means that the sensor receives less light than a conventional SLR: some of the light is reflected up into the focus sensors near the viewfinder. It remains to be seen if this loss of light affects performance, particularly when shooting in low light.

The Alpha SLT-33

Both cameras are equipped with APS-C sized CMOS sensors, with the A55 capturing 16.2 megapixel images and the A33 capturing 14.2 megapixels. Sony claims that the combination of an Exmor CMOS sensor and a new Bionz image processing engine allows for a wide ISO range of 100 to 12,800, as well as offering the 3D sweep panorama shooting that we have seen on several Sony compact cameras which allows the camera to capture a wide panorama in a single shot. The two new SLRs are also the first to offer another feature that was pioneered on Sony point & shoot cameras: several modes that combine multiple images into one for better noise reduction, low light shooting and motion removal.

The two new SLRs also both include articulated 921k LCD screens that can flip up or down and rotate to allow shooting from above or below. They can also be flopped down below the camera body to allow for self-portraits, and rotated so that the screens are protected from damage when not in use. And like all of Sony's recent point and shoot models, the new SLR cameras support both Sony's own Memory Stick Pro and SDHC memory cards, including the recently released faster and higher capacity SDXC versions.

The rotating LCD screen of the Alpha SLT-55

Both cameras can also capture Full HD video with a resolution of 1920 by 1080 pixels, which is stored in AVCHD format that can be edited in programs such as iMovie. The video is captured at 60 frames per second, but these are interlaced frames, not the full progressive that other SLRs can capture. The new cameras do offer a 30 progressive frames a second mode, where the video is stored as MPEG-4 video.

The lens mount for the cameras is the same A-mount used on previous Sony SLRs, so the new models will be compatible with lenses designed for previous models. The A55 will cost $750 for the body only, or $850 for the body and an 18-55mm kit zoom lens and will be available in September. The A33 will cost $650 for the body, or $750 for the body and kit lens, and will be available in October.