Getting started with the Nikon Z6 III: the ISO increase of the sensor in detail

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Brand new hot, the freshly announced Nikon Z6 III has arrived at the lab Digital. We will certainly have to wait a little (patience!) for a complete test, but we have already warmed up the new 24×36 24.4 Mpx sensor against our famous test pattern.

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A sensor that has its importance in the equation since Nikon presents it as the first sensor “partially multi-layered“. Here, a small technical point is necessary. Nikon's formula – which always has somewhat confusing in-house translations! – corresponds to what is called in the jargon a stacked sensor.

© Adrian BRANCO for Les Numériques

Industrialized by Sony, first in small smartphone sensors, the stacking of several layers of electronics makes it possible to move the circuits, notably the analog-to-digital converters (A/D converters), not next to the colored sub-pixel , but below.

Structure of a fully stacked CMOS sensor: moving the logic circuits under the pixels makes it possible to better isolate the signals, improves production yields and offers more surface area and therefore more computing power and/or memory. The challenge being to adjust the components to the tenth of...

Structure of a fully stacked CMOS sensor: moving the logic circuits under the pixels makes it possible to better isolate the signals, improves production yields and offers more surface area and therefore more computing power and/or memory. The challenge is to adjust the components to the nearest tenth of a nanometer!

© Sony Semiconductor Solutions Group

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There are several advantages to this. The first is to limit electromagnetic pollution around the photodiode by moving the circuitry to another layer. The other is the additional space for the circuitry that this provides: with a classic design, the surface area is very limited. By taking advantage of its own dedicated layer for the components (converters, but also memory), the sensor designer can benefit from increased processing power and a surplus of information storage memory, while pushing higher the playback frequencies.

Marketing image of the Nikon Z6 III CMOS sensor. Note the two horizontal bars at the top and bottom of the photosensitive surface, which are the logic circuits added to improve reading speed.

Marketing image of the Nikon Z6 III CMOS sensor. Note the two horizontal bars at the top and bottom of the photosensitive surface, which are the logic circuits added to improve reading speed.

© Nikon

This sensor design costs more, because it is often necessary to design the electronics on another silicon wafer and stick it with very high precision behind the photosensitive part. To limit the increase in cost, Nikon placed the additional components not below its pixels, but next to the photosensitive part, on the front of the sensor, outside the image circle.

© Adrian BRANCO for Les Numériques

On the one hand, the quantity of circuits to add is less than with a truly stacked sensor, on the other hand, positioning requires less precision — in the case of a truly stacked sensor, each pixel is connected to a converter dedicated ! If the burst values ​​will be evaluated in the field, the question was therefore whether this design had an effect on the rise in high sensitivities.

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Steps at 1600 and 6400 ISO

COMPARISON ISO Z6 III - EOS R6 II - A7 IV

We compared its increase in ISO with two direct competitors: the Sony Alpha A7 IV and the Canon EOS R6 Mark II. The first has a 30 Mpx sensor, the other 24 Mpx. And their positioning in the range and price at launch is close.

What we immediately notice is the intensity of the smoothing at the 1600 ISO level. While details are perfectly preserved up to ISO 800, we notice that the image quality deteriorates on the Nikon Z6 III. A loss of precision also present with the Canon EOS R6 Mark II, but a little less significant. As for the Sony A7 Mark IV, it has the triple luxury of pushing this threshold to ISO 3200, with less loss of precision and superior definition.

Nikon Z6 III ISO Upgrade

As sensitivity increases, the quality of the Nikon gradually deteriorates, as with the Sony. The exception being Canon which, although less accurate overall at lower ISO values, offers the most consistent degradation up to ISO 51,200. Beyond that, we find ourselves faced with pixelated watercolor in all the protagonists.

Although this is only a first test shot, we can however suspect one thing in the Nikon Z6 III sensor: its very high reading speed seems to have an impact on its image quality. With a raw burst of up to 20 fps and jpeg bursts of 30 to 120 fps, the Z6 III targets sports and action photographers. However, as we have seen on ultra-fast sensors, in particular the global shutter sensor of the Sony A9 Mark III, the very high reading speed requires electronics (A/D converters, etc.) that consume energy and generate more interference – and therefore digital noise – than slower sensors. Nikon's dual ISO circuit helps limit damage and provides good image quality up to ISO 6400.

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Note here that this is an evaluation of the quality of jpeg compression by default. It will also be necessary to evaluate what the raw files produce when they are handled by demosaicing software. And determine, at that moment, the acceptable limit values ​​in terms of image quality – modern noise reduction algorithms are now doing an astonishing job.

There cameraness from Nikon hits the mark

© Adrian BRANCO for Les Numériques

Although we will have to wait for the test to have a final opinion on the case, a first visit to the lab and a few manipulations allow a first evaluation… quite subjective. If Nikon's nature and sport DNA means that large bodies like the Z9 and Z8 make perfect sense with the quality long focal length lenses that the company markets, the fact remains that they are bulky and heavy. .

© Adrian BRANCO for Les Numériques

While it may not have the compactness of some cameras, notably Sony's A7C II/R, the Z6 III is nevertheless more compact, lighter and more manageable than its big brothers, while maintaining an excellent impression of robustness and reliability. A feeling that Nikon had conceptualized with the portmanteau word cameraness. A cameraness which allows the Z6 III to really stand out from the competition from Sony and Nikon, without having to pay too high a price in terms of weight and size. Here we feel the ergonomic know-how of the brand's case engineers!

© Adrian BRANCO for Les Numériques

However, we regret that Nikon does not offer many compact lenses. Indeed, its 40mm f/2.0 does not offer stellar image quality. And Converselyits Nikkor Z 50mm f/1.8 S may be very good, but it is a bit bulky with its 8.7cm barrel.

And the rest of the test? In addition to field trips and other AF measurements, we will have to wait for Mr. and Mrs. Adobe to integrate support for raw files into CameraRAW. It will be necessary at least this in order to evaluate the image quality of this singular sensor, partially stacked…

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