The highest resolution Full-Frame Digital Camera on the market just got ranked by DxOMark. The Sony Alpha A7R IV packs a 61 megapixels BSI-CMOS sensor with a built-in 567-Point Phase-Detect AF system which is mounted on a 5-axis image-stabilization system effective to 5.5-stops. Sony splits there mirrorless lineup into the A7 lines of which the A7R is the highest resolution offering and the A9-series designed for action photography.
DxOMark just released their score for this high-resolution mirrorless, tied against the Nikon Z7 in 6/7th place with a score of 99. This is actually the second highest score of all full-frame cameras with the Panasonic S1R, Nikon D850 reviewed here and Sony A7R III all reaching 100. Only two Medium-Format cameras score higher. The interesting point here is that the IV version scores just below its predecessor which sports a 42 megapixels BSI-CMOS sensor instead. Of course, the lower resolution with the same sensor area means that each pixel of the Sony A7R III is larger and collects more light than those on the A7R IV.
Breaking down the score into its three components, this camera delivers 14.8 EV Dynamic-Range, 3344 High-ISO in unspecified units and 26 bits of color-depth. This is the maximum dynamic-range measured by DxOMark among any camera. While each pixel gathers less light, noise levels must be so low that the A7R IV makes it possible to distinguish details in 14.8 EV. This makes this mirrorless superb for landscape photography.
The amount of colors a camera can distinguish is what is measured as bit-depth. At 26 bits, this Sony falls within the top 10, joining the range shared by Full-Frame and Medium Format digital cameras. Anything above 24 is unnoticeable in prints and even the vast majority of computer displays. Although some do 30-bits, there are almost no applications that can exploit the added bit-depth.
With a High-ISO score of 3344, the Sony Alpha A7R IV again falls within the top 10 which is an excellent performance considering the extremely high resolution of its sensor. In the method used by DxOMark though, it is important to know that these measurements are normalized and measured scaled down. Otherwise, this mirrorless has relatively high per-pixel noise. This means that larger prints will not show the performance one would expect for such a high ranking.
The big question which remains is the difference between the A7R IV and A7R III which precedes it. Looking at scoring, they perform nearly identically. Both deliver the same 26-bit color-depth, while the III performs slight better at High ISO and captures just 0.1 EV less dynamic-range. The one that comes out better depends the weighting used to combine the scores. In practical terms, the A7R III should be preferred in low-light and the A7R IV will produce larger prints in bright light.
With a DxoMark score of 99, the Sony Alpha A7R IV finds itself among the best-performing digital cameras to date. The fact that Sony managed to maintain this level of image-quality with nearly 50% more pixels is simply extraordinary.
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