At a time when many new interchangeable-lens cameras have been forgoing reflex mirrors altogether, Sony’s new Alpha 55 (and Alpha 33) take a radically different approach. Instead of ditching the mirror—and with it, speedy, reliable autofocus—Sony gave these two DSLRs a semi-transparent mirror that doesn’t flip up and down. The result: Cameras that can autofocus continuously while recording high-definition video, and fire off stills at high burst rates—and that keep the existing Alpha lensmount for compatibility with the entire Sony lens catalog. They’re also smaller and lighter than Sony DSLRs in the same class.
Dubbed Translucent Mirror Technology by Sony, this sort of device is hardly new—in fact, it dates back nearly half a century. But the A55 and A33 are the first digital cameras to employ mirrors that let most of the light pass through to the imaging sensor and simultaneously reflect a small portion of it upward to the AF module. The cameras also differ from fixed- mirror designs of the past in that they have an electronic viewfinder (EVF) instead of an optical prism finder.
Other than different sensors and different Speed-Priority burst capacities, the A55 ($750, street, body only; $850 with 18–55mm f/3.5–5.6 Sony DT SAM lens) and A33 ($650, street, body only; $750 with the same lens) are identical. We’ve therefore covered the two models in this single test report. Note: Our A55 test model was actually the A55V, which has built-in GPS; the non-GPS A55 is not marketed in the U.S.
In the Test Lab
An obvious question was how the fixed mirror affects image quality and performance. In the Popular Photography Test Lab, the A55 and A33 delivered images in line with what we’ve come to expect from mid-range Sony DSLRs. Both cameras scored Extremely High in color accuracy, just below the threshold for an Excellent rating—a respectable result, but below the performance of the vast majority of today’s DSLRs.
Resolution was the same story, with both cameras turning in good numbers that weren’t quite what we’d expect for cameras with their pixel counts. The 14.2MP A33 served up 2125 lines per picture height for a Very High rating, putting it behind Sony’s own 14.2MP A550 DSLR (2285 lines) and Panasonic’s 12.3MP Lumix DMC-G2 inter changeable-lens compact (2230 lines). The 16.2MP A55 yielded 2290 lines in our test for an Extremely High rating, although not very far ahead of the A550 and G2.