DxOMark is the industry’s leading source for high-end metrics on camera sensors and lenses, and the company have compared the image quality of the a7II, a7S and a7R cameras in this excellent, in depth review. DxO performs detailed analysis of image and sensors for their excellent suite of software, and the findings are used to evaluate and rank cameras on the DxOMark site.
The article reveals some expected but also some unexpected findings. On the sensor quality of the a7R the site writes.
with a DxOMark Sensor Score of 95 points that ranks it 3rd overall on the database. The A7R’s score of 95 represents a 1/3rd stop better image quality overall than 24.2Mp A7II with 90 points, and a ½ stop improvement over the 12.2Mp A7S with 87 points…
That’s to be expected, the Sony sensor in the a7R is truly astounding so we’re not surprised to see that it ranks so high.
What we didn’t expect though is the finding that the small-sensor a7s doesn’t score as well as the a7R when it comes to dynamic range at its base (lowest) sensitivity.
At base sensitivity of ISO 50 the best Colour Depth and Dynamic Range scores on the A7II and A7R offer notably better results than those from the lower resolution A7S’s 12Mp sensor. Achieving 25.6 bits for Colour Depth and 14.1 Evs for Dynamic Range the A7R offers a whole stop better image quality than the A7S in both categories. The new A7II sits between the A7S and A7R for Colour Depth and Dynamic Range offering a good compromise between resolution, Colour Depth and Dynamic Range.
Many people who have purchased the a7s have done so to take advantage of the theoretical better dynamic range offered in a sensor with fewer pixels than the same size sensor with more pixels. But at least at the low ISO range of the sensor, the a7R performs better.
Update
After publishing this article we received a nice email from DxO, who asked us to point out that the range of the A7s improves pretty drastically at higher ISO. Here’s the chart he sent from their testing.
Clearly the camera starts to beat the A7R in dynamic range between ISO 200 and 600 and is a full stop better by around ISO 4000. At that point it keeps going—and the a7S s capable of capturing images above ISO 25600, where the a7R has its upper-end limit.
We highlighted the fact that the a7R has better dynamic range at base ISO (and indeed up to ISO 200 or so) because every photographer we know that’s considered the a7S over the a7R has stated that they wanted to get better dynamic range and lower noise. Obviously dynamic range and noise are not the same, but we wanted to point out the fascinating metrics DxO uncovered at base ISO.
A good takeaway here is that studio photographers would do better to buy the a7R and to control lighting to keep the camera in the ISO 100-200 range than to purchase an a7S at that same ISO range.
The article is full of incredible metrics and graphs covering the performance of every aspect of the sensors and is worth a read. We’re particularly fond of this line from the conclusion “We will have to wait and see if the other manufacturers release an alternative full frame hybrid camera to rival Sony’s A7 series in 2015, but for now it remains a unique proposition in the market.”
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