I am convinced Sony will go in the direction of Quad Bayer stacked CMOS sensors for the A7S series and it’s a major reason we’ve waited so long for it. I also think the FS5’s electronically variable ND filter will be in the camera too.
Quad Bayer answers the conundrum of balancing low light performance and megapixel count. It is the best of both worlds and allows a 48 megapixel 8000 x 6000 image and 8K video – at the same time as 4000 x 3000 and 4K video with better low light performance.
The proof of concept is sitting in my hands right now. Step forward the mighty Xiaomi Mi 9 smartphone with 48 megapixel Sony Quad Bayer sensor and 960fps slow-mo.
Until recently Quad Bayer sensors have been seen in the Huawei photography flagships – the P20 Pro and P30 Pro. These however were standard designs. Sony now has a stacked Exmor RS version which enables the much faster readout for 8K video and even 1080p at 960fps (IMX 586 full specs here).
The first smartphone with this sensor to make use of 8K video is a gaming handset by ZTE but I am currently taking the same sensor for a test drive in a better all-round phone, the Xiaomi Mi 9 which rivals the P30 Pro and in my opinion beats it for stills and video quality.
Quad Bayer gives the sensor the ability to debayer in such a way that pixel size varies. The photodiode size on the Xiaomi Mi 9 smartphone sensor for example is incredibly small at just 0.8 micron, 10x smaller than a grain of pollen. Until now the manufacturing techniques haven’t been able to make a pixel design at this small of a pitch, due to cross talk and leakage between pixels. Now this problem has apparently been overcome.
A Quad Bayer sensor can double the pixel size at the expense of resolution. Thus the Xiaomi Mi 9 can output 8000 x 6000 images at 0.8 micron for the highest resolution in bright light, or do 4000 x 3000 images at 1.6 micron for the best low light performance I’ve yet seen in any smartphone, beating the Samsung S10+ and Pixel XL 3 with their standard 1.4 micron 12 megapixel sensors. What’s more the Mi 9 Transparent Edition has an F1.47 aperture 7 element lens compared to the F1.75 lens on the standard version and other similar smartphones.
Now it’s easy to see why this sensor could suit the A7S III, as well as the A7R III.
The “dual-native” resolutions of a Quad Bayer sensor could mean Sony will eventually put the exact same sensor in the A7R III and A7S III, with different implementations in the image processor. The A7R III could output 48 megapixel stills and 4K video. The A7S III could output 12 megapixel stills and 8K video.
The stacked Exmor RS design allows the very fast readout. Benefits of that include 8K video and a full pixel readout 4K mode, high frame rate 1080p (up to 960fps), less rolling shutter and a crisper, more detailed live-view display with faster frame rate. In the phones that implement the stacked 48 megapixel sensor, video quality is far superior to the previous 40 megapixel sensor, a bit of a weak-point of the Huawei P20 Pro (and still is on the P30 Pro).
What is striking though about the latest Quad Bayer design from Sony is just how clean the low light performance is in video mode. You don’t even need to pixel peep the files, just hold up the Mi 9 and P30 Pro side by side. One is incredibly crisp and creamy under dim indoor lighting and the other is a pixilated mess in live-view. Then you take a look at the RAW results in 12 megapixel mode – wow is all I can say to that. ISO 9000 giving usable results on a smartphone? On a 48 megapixel sensor? Yes sir.
If this design of sensor is scaled up to a full frame chip, that my friends, is mission accomplished. Ultra high resolution 8K video without sacrificing low light performance in 4K or 12 megapixel stills mode. If the A7S III or IV is to go 8K, Quad Bayer is the way to do it.
I have a feeling we may see a smaller sensor first though – in particular a Micro Four Thirds size Quad Bayer sensor in the GH6 with a resolution of between 38 and 48 megapixels. This would solve the low light weakness of the Micro Four Thirds format at the same time as answering the call for higher resolutions than 20 megapixel. This will allow the system to keep pace with APS-C and full frame sensors as these escalate.
And Quad Bayer also allows far higher resolutions than 48 megapixels on a full frame sensor. That number is currently the limit on a smartphone due to the incredibly small pixel pitch needed for the manufacturing process at 0.8 micron. There’s no such limit on a full frame sensor even at 100 megapixel.
It appears Sony has a clear road-map and way forward to delivery astounding gains in performance.
Other manufacturers (especially Canon) better hope it can develop it’s own Quad Bayer sensors without infringing Sony’s patents or paying to license their designs, otherwise they are going to really struggle to match the performance of Sony’s chips in video mode and in low light on high resolution designs.