Today, DxOMark released their scoring of the Sony Alpha A99 II, the latest Sony SLT Full-Frame camera featuring the same 42 MP CMOS sensor as the highly-acclaimed Sony Alpha A7R II which is a traditional mirrorless camera.
DxOMark scores the Sony Alpha A99 II at 92, an excellent score by all means. Breaking it down into its three component scores, the A99 II manages 13.4 EV of Dynamic-Range, 2317 High-ISO points and 25.4 bits of color-depth. The unusually low score of 2317 for ISO on a full-frame is quite telling of the compromise brought by SLT technology.
The Sony Alpha A7R II by contrast scores 98 on the DxOMark scale. This is made of 13.9 EV of Dynamic-Range, 3434 High-ISO points and 26 bits of color-depth, meaning that the A7R II beats the A99 II on all counts. Its high-ISO score in particular is 50% higher, leaving the SLT camera in serious doubts when it comes to low-light performance.
Recall that the A99 II uses a translucent mirror to send part of the light to a dedicated AF sensor and the rest to the imaging sensor. By all acounts, it blocks 1/3 of light from reaching the sensor. This forces Sony to raise the gain on the read-out to maintain the same ISO as the A7R II. This really makes the cost of SLT technology unnaceptable. In truth, SLT lost most of its advantages with the integration of on-sensor Phase-Detect AF which the A99 II also features.
While this could spell the end for Sony SLT digital cameras, it does not necesarily imply the same for the A-mount. They could simply remove the SLT mechanism and create a series of A-mount mirrorless. Unfortuntaly there would be very little advantage to this over an E-mount mirrorless which can still fully use A-mount lenses via one of Sony’s excellent adapters.