Analyzing the Sony A7R Sensor

Oct 18, 2013
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There has been a great deal of discussion in the blogosphere as to whether the newly announced Sony A7R (and the A7) have brand new sensors (which Sony claims) or Sony is merely recycling existing sensors crammed into smaller bodies. Without having my hands on an actual camera, I can only go with the materials presented on the Sony website.

First, a preamble: I am not an electrical or optical engineer. I am a professional photographer and a software/systems engineer by trades & training. I have been a professional systems analyst for close to 30 years. 

Second, all of this information is taken from the Sony A7/A7R mini site and I am going to assume that they are not lying through their teeth. I am going to confine this analysis to the sensor in the A7R, but I imagine that much of it will apply to the A7.

Third, I am not being compensated, paid, favored, or coerced by Sony or any of it’s affiliates, marketing companies, subsidiaries, relatives or neighbors.

There, now that all of that disclosure BS is out of the way, lets get this show on the road.

This first panel is simply stating Sony’s claim that the sensors are new, of the highest quality, using the latest technology, all promising to make you an awesome photographer. In short, an executive summary.

The second panel has some real meat on it. The sensor is an Exmor sensor. From Wikipedia: 

Exmor is the name of a technology Sony implemented on some of their CMOS image sensors. It performs on-chip analogue/digital signal conversion and two-step noise reduction in parallel on each column of the CMOS sensor. It can help to reduce the amount of “seen” pixels when you’re zoomed in on a photo.

Exmor should not be confused with Exmor R, Sony’s trade name for backside illuminated sensor technology, which is restricted solely to small, high-density sensors for compact cameras, cellphones, etc. Unlike Exmor R, Exmor is not limited to use in smaller sensors, and its benefits are just as applicable in the larger APS-C sized sensors featured in DSLRs.

So the sensor tech used is Sony’s proprietary design that has on-chip A/D converters and noise reduction occurring while the image is being captured. It is my understanding that this technology is present in the D800 & D800E sensors although it might just be a derivative form.

No low pass filter. On the D800E, the low pass filter is “neutered” not removed. The secondary beam splitter in the low pass filter was mounted backwards to recombine the light that was split by the primary beam splitter, effectively neutralizing the effect of the low pass (antialiasing) filter. The A7R micro site claims that there is no low pass filter but there is a protective layer that more than likely contains as IR filter.

The marketing blurb at the end reminds us that Sony makes the largest amount of camera sensors in the world.

Gapless, optimally positioned on-chip lenses: “on-chip lenses” refers to what he’s been previously called “micro lenses”. These are tiny lenses mounted directly over the Bayer filters that concentrate and direct the light to the sensor underneath. “Gapless” means that these micro lenses are butted up against each other, maximizing their light-gathering capabilities. The text states that the lenses are “optimally positioned” which means that the lenses towards the edges of the sensor are slightly skewed to better capture the light that is entering the sensor at oblique angles. Due to the E/FE-mount’s short registration distance (the distance from the lens flange to the sensor), light towards the edges will be coming in at sharp angles. The skewed micro lens arrangement compensates for that.

BIONZ X is Sony’s latest central processor design. This is the heart of the camera, where all the processing magic happens that turns the collection of data that the image sensor provides into an actual image. LSI chips are secondary systems that accelerate the whole process.

This section refers to improved methods for sharpening the image while reducing edge over sharpening. Lens diffraction (diffraction occurs when the aperture closes down to a point where the diameter is approaching the wavelengths of the light being captured which in turn, causes backscatter) can lead to image blur at very small apertures. This technology reduces the effect by applying localized sharpening and micro contrast.

Similar to the aforementioned diffraction compensation, this feature applies localized noise reduction in order to maintain the maximum amount of detail at high ISO values.

The Exmor sensor captures image data with 14-bits of color resolution per channel. This means that any given image can contain up to 4,398,046,511,104 (4 trillion 398 billion 46 million 511 thousand 104) colors. That’s a lot of crayons in the box. The 16-bit image engine is capable of handling quadruple that amount of color. When the image is saved, the JPEGs contain 8-bits per channel of color info and the RAW files have the full 14-bits per channel. RAW converters can push the colorspace back up to 16-bits per channel.

CONCLUSION

Based on the information provided by Sony, it is safe to say that the sensor used in the A7R is not the same sensor from the D800E. It is more like the second generation version of said sensor.

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