Camera
Sony a9 III: Global shutter comes with an image quality cost
We’ve just had the chance to put a production Sony a9 III through our studio scene. The question we most wanted to answer was: is there any image quality cost to adopting a global shutter sensor? The short answer is: yes.
Global shutter sensors have been available and used in industrial settings for some time now, but haven’t made their way across to photography because the more complex design meant their image quality wasn’t a match for the best progressive-scan CMOS designs. Sony said the a9 III’s Stacked CMOS design overcame any compromise in ISO or dynamic range. This doesn’t appear to be the case.
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However, in the context of a professional sports photography, the compromises that have been made may well make sense, in return for the sheer speed of capture the a9 III is capable of, both in terms of burst rate and its fast, distortion-free shutter.
The most immediate difference in capability is that the a9 III has a base ISO of 250. This means that you can’t give it as much light as its peers with base ISOs of 100 or lower. This is not necessarily an issue for sports photography, where maintaining a high shutter speed is much more important than the need to optimize image quality by staying at a low ISO.
Has the studio scene changed?The a9 III is one of the first cameras we’ve shot since setting up our studio scene at our new location. Our a7CR images raised concerns about how consistent the results are between the new installation and our previous setup. In response to these concerns, we re-shot the Sony a7R V (whose higher resolution viewfinder makes it much easier to fine-focus than the a7CR) and checked the Raw values against the photos taken in the old studio. With some slight adjustment of the lights, we reduced the existing 0.08EV discrepancy down to 0.02EV difference for the grey patches we use for noise assessment. We wanted to make sure that both we and our audience could have complete faith in the consistency of the test scene before testing the a9 III. The files shot on Jan 2nd 2024 and the original versions, as featured in the comparison tool, shot on Nov 11 2022, can be downloaded here. |
What might be of more concern to sports shooters is that the high ISO performance appears to be as much as one stop noisier than its full-frame rivals, especially as you reach its highest ISO settings. There’s a noticeable softness to the ‘grain’ pattern in the a9 III’s images too, which we suspect is the result of noise reduction being applied in the Raws.
This is in line with what we expected. Essentially the a9 III’s sensor works by having two photodiodes at each pixel: one to capture the light, initially, and the second to act as a holding buffer, that allows all the pixels to be read-out simultaneously. This design effectively halves each pixel’s capacity for light, which explains the elevated base ISO and the decreased noise performance, which brings it closer into line with the performance of APS-C cameras. In addition, the complexity of the design means we don’t get the dual conversion gain circuitry that helps improve high ISO performance on other recent cameras.
How does the a9 III’s dynamic range compare?
Just as staying at low ISOs is rarely critical for sports, nor is maximizing dynamic range for a discipline that generally shoots JPEGs for immediate delivery, with no time to exploit extra DR during careful processing as, for instance, landscape shooters might.
The sensor’s reduced capacity for light has an impact on dynamic range, since the entire image becomes noisier, but we should be careful not to double-count this by interpreting it as a separate dynamic range cost. At its launch, Sony told us the a9 III has dynamic range comparable with previous models, and our measurements show that it is comparable with cameras when operating at ISO 250. Notably most other cameras can operate at lower ISOs than this, and hence have a higher maximum dynamic range than the a9 III.
When compared, the Sony a9 II, if anything, shows more noise if shot at its ISO 200 setting when brightened, than the a9 III. The a9 III’s smaller photodiodes mean there’s more photon shot noise in the ISO 6400 shots (simply because the Mk III captured less light), but if you try brightening the low ISO files there doesn’t appear to be an additional (electronic) read noise cost. It’s the same story if you try to reduce exposure at base ISO and brighten: the a9 III is a little behind the a9 II because its base ISO is higher, but there’s not a big difference in additional noise if you compare similar exposures (where photon shot noise would be similar so differences caused by read noise would become apparent).
Summary
Examining the a9 III’s images shows everything that you’d expect from it having a reduced capacity for light. The higher base ISO isn’t inherently a problem for sports shooters, so it’s simply a question of whether the noise penalty is worthwhile for all the things that super-fast 120fps shooting and global shutter bring. That’s something we’ll consider in more depth in our final review.
But what does this trade-off mean beyond the pro sports market? Our tests show that this sensor’s performance comes with an image quality hit that might make less sense for general photography. Furthermore, this cost of up to a stop of image quality in return for added performance is likely to make global shutter less appealing in the smaller APS-C and Four Thirds formats, which don’t have the luxury of so much IQ to give up.
Overall, the a9 III still looks promising, for its intended purpose, but it shouldn’t be assumed to herald the future of cameras as a whole.
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Camera
Pentax K-1 and K-1 II firmware updates include astrophotography features (depending on where you live)
Yesterday, Ricoh quietly released firmware 2.50 for its Pentax K-1 and K-1 II DSLRs. However, the features you can expect to gain from this update may depend on your geography.
Ricoh’s English-language firmware pages for the K-1 and K-1 II state that firmware 2.50 delivers “Improved stability for general performance.”
However, astute Pentax users noted that Ricoh’s Japanese-language firmware pages (translation) indicate that the update also includes a limited feature called “Astronomical Photo Assist,” a collection of three new features designed for astrophotography: Star AF, remote control focus fine adjustment, and astronomical image processing.
Star AF is intended to automate focusing on stars when using autofocus lenses. Rather than manually focusing on a bright star and changing your composition, it promises to let you compose your shot and let the camera focus.
Remote control fine adjustment allows users to adjust focus without touching the lens and requires Pentax’s optional O-RC1 remote. Astronomical image processing will enable users to make in-camera adjustments to astrophotography images, including shading correction, fogging correction, background darkness, star brightness, celestial clarity, and fringe correction.
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| Astronomical image processing on the K-1 and K-1 II will enable users to make in-camera adjustments to astrophotography images, including shading correction, fogging correction, background darkness, star brightness, celestial clarity, and fringe correction. |
According to Ricoh, Astronomical Photo Assist is a premium feature that must be purchased and costs ￥11,000 for an activation key (about $70 at current exchange rates).
Although these astrophotography features appear to be Japan-only for now, a Ricoh representative tells us, “Ricoh Imaging Americas confirmed that the premium firmware features for the PENTAX K-1 and PENTAX K-1 Mark II will eventually be available to US customers.”
Firmware update 2.50 for both the K-1 and K-1 II is available for download from Ricoh’s website.
As part of our twenty fifth anniversary, we’re looking back at some of the most significant cameras launched and reviewed during that period. Today’s pick was launched seven years ago today* and yet we’re only quite recently stepping out of its shadow.
The Nikon D850 is likely to be remembered as the high watermark of DSLR technology. We may yet still see impressive developments from Ricoh in the future (we’d love to see a significantly upgraded Pentax K-1 III), but the D850 was perhaps the green flash as the sun set on the DSLR as the dominant technology in the market.
Click here to read our Nikon D850 review
Why do we think it was such a big deal? Because it got just about everything right. Its 45MP sensor brought dual conversion gain to high pixel count sensors, meaning excellent dynamic range at base ISO and lower noise at high ISOs. Its autofocus system was one of the best we’ve ever seen on a DSLR: easy to use and highly dependable, with a good level of coverage. And then there was a body and user interface honed by years of iterative refinement, that made it easy to get the most out of the camera.
None of this is meant as a slight towards the other late-period DSLRs but the likes of Canon’s EOS 5DS and 5DSR didn’t present quite such a complete package of AF tracking, daylight DR and low-light quality as the Nikon did. With its ability to shoot at up to 9fps (if you used the optional battery grip), the D850 started to chip away at the idea that high megapixel cameras were specialized landscape and studio tools that would struggle with movement or less-than-perfect lighting. And that’s without even considering its 4K video capabilities.
In the seven years since the D850 was launched, mirrorless cameras have eclipsed most areas in which DSLRs once held the advantage. For example, the Z8 can shoot faster, autofocus more with more accuracy and precision, across a wider area of the frame and do so while shooting at much faster rates.
But, even though it outshines the D850 in most regards, the Z8 is still based around what we believe is a (significant) evolution of the same sensor, and its reputation still looms large enough for Nikon to explicitly market the Z8 as its “true successor.”
Nikon D850 sample gallery
*Actually seven years ago yesterday: we had to delay this article for a day to focus on the publishing the Z6III studio scene: the latest cameras taking precedence over our anniversary content.
| Photo: Richard Butler |
We’ve just received a production Nikon Z6III and took it into our studio immediately to get a sense for how the sensor really performs.
Dynamic range tests have already been conducted, but these only give a limited insight into the image quality as a whole. As expected, our Exposure Latitude test – which mimics the effect of reducing exposure to capture a bright sunrise or sunset, then making use of the deep shadows – shows a difference if you use the very deepest shadows, just as the numerical DR tests imply.
Likewise, our ISO Invariance test shows there’s more of a benefit to be had from applying more amplification by raising the ISO setting to overcome the read noise, than there was in the Z6 II. This means there’s a bigger improvement when you move up to the higher gain step of the dual conversion gain sensor but, as with the Z6 II, little more to be gained beyond that.
These are pushing at the extreme of the sensor’s performance though. For most everyday photography, you don’t use the deepest shadows of the Raw files, so differences in read noise between sensors don’t play much of a role. In most of the tones of an image, sensor size plays a huge role, along with any (pretty rare) differences in light capturing efficiency.
As expected, the standard exposures look identical to those of the Z6 II. There are similar (or better) levels of detail at low ISO, in both JPEG and Raw. At higher ISO, the Z6III still looks essentially the same as the Z6II. Its fractionally higher level of read noise finally comes back to have an impact at very, very high ISO settings.
Overall, then, there is a read noise price to be paid for the camera’s faster sensor, in a way that slightly blunts the ultimate flexibility of the Raw files at low ISO and that results in fractionally more noise at ultra-high ISOs. But we suspect most people will more than happily pay this small price in return for a big boost in performance.
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