A New Breed of Camera

I first laid my hands on the Sony Alpha A55 (and the smaller, less expensive Alpha 33) at the PhotoPlus Expo in New York City last September.

What interested me in this new camera was its fixed translucent mirror. In a conventional DSLR, the reflex mirror reflects the image into the viewfinder and then swings out of the way when you press the shutter to send the image to the “film” light sensor. In the Alpha 55, the translucent mirror sends a small portion of the incoming image to the viewfinder and the remainder to the “film” light sensor. This stationary mirror gives the camera several unique features that I’ll describe shortly. This technology isn’t new. In the early 1960′s Canon made a model called the Pellix using a similar scheme with a pellicle mirror. My uncle bought this camera back then, one of the first to have Through The Lens metering (TTL) and it served him well for many years.

The A55’s translucent mirror eliminates the reflex mechanism providing a space, weight and cost savings. Removing this mechanical assembly also allows for a higher frame rate. Next, the electronics measuring the auto exposure remain uninterrupted from frame to frame giving instant responses to varying changes in lighting. Similarly, the auto focus system stays 100% available – a very important consideration for high speed continuous shooting.

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