You’ve probably read plenty of articles touting the benefits of Sony’s translucent mirror technology (e.g. high fps, AF for video, quietness, etc…), but what about the cons? One of the main downsides to having a translucent mirror is that the light hitting the sensor passes through an additional layer (the translucent mirror), which reduces the amount of light and the image quality.
Ray over at TheSyberSite attempted to quantify how much the mirror affects the resulting image quality by removing the mirror on his A55 and comparing the resulting photos. He confirmed that about 1/2 stop of light is lost, and estimates that 5% of the detail in each shot is lost due to the mirror. Head on over to the article for some side-by-side comparisons.