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Sony a9 III
The Sony a9 III is the latest in the series of high-speed cameras that was the first to bring Stacked CMOS technology to the mirrorless camera market. The new model is the first mirrorless camera to offer a truly global shutter: one where all its pixels are read out simultaneously.
This means the a9 III doesn’t need a mechanical shutter, since the sensor can do everything a mechanical shutter can do, and more. While this isn’t everything the a9 III offers, it underpins much of what sets it apart from the other sports cameras on the market, so that’s where we’ll start.
Global shutter – No distortion, 120 fps
The most obvious benefit of using a global shutter is that there’s no risk of distortion if the subject moves quickly across the frame. This is true in both stills and video, meaning the a9 III can shoot very fast-moving subjects with no risk of distorted verticals.
This makes sense for a camera that can shoot at 120 frames per second and pre-buffer to capture action. A camera designed for capturing very fast bursts of motion wouldn’t work if it warped and distorted that motion.
Sony clearly recognizes that 120fps isn’t the right mode for most shooting, so has added a custom button option that lets you engage up to 120fps shooting while the button is held down, allowing you to focus your bursts just on the critical moments. This ‘Continuous Shooting Speed Burst’ button can be set to invoke anything from 5fps to 120fps, depending on your needs.
Global shutter – sync at any speed
The benefit of the global shutter that more users are likely to experience is the ability to flash sync at any speed. Progressive shutters (whether electronic or mechanical) take a certain amount of time to start or end an exposure, and the camera’s sync speed is typically defined by this rate. The rate at which exposure can be started and stopped defines the maximum amount of time the whole sensor can be fully exposed before the second curtain has to begin the process of ending the exposure. To use flash beyond this point requires the use of high-speed sync: pulsing the flash to ensure even exposure with the sensor only partially exposed.
Global shutter entirely eliminates this problem: all pixels are captured simultaneously, so the only challenge comes if the burst of flash itself lasts longer than the exposure. The camera will try to sync at shutter speeds up to 1/80,000 sec. This ability to use short exposures means that, as with leaf-shutter systems, you can control the background exposure even in bright light, while still using flash to illuminate your subject.
Sony’s own F46RM and F60RM2 flashes can sync up to the maximum shutter speed. Third-party flashes may see reduced brightness if you use a shutter speed shorter than the duration of their flash burst. If this occurs, you can adjust the tiny delay that occurs before the flash is fired, to help increase the overlap between the flash’s peak output and the exposure.
Global shutter – no banding
The other problem global shutter overcomes is that there’s no risk of capturing different parts of an LED advertising panel’s flick in different parts of your image. This could cause banding which is particularly pronounced when using an all-electronic progressive shutter. The a9 III captures the entire scene as a single moment in time, so there’s a risk of shooting an LED panel part of its way through refreshing, but not of capturing multiple points in that refresh, and hence no banding.
When working under LED illumination, there’s a risk of varying exposure, shot-to-shot, as the light flickers, but the a9 III has an Anti-Flicker mode that measures the flicker of the lights, then syncs the taking of photos with the brightest point in the flicker cycle, meaning you don’t get dark or miscolored images during bursts, even under flickering lights.
The challenge of global shutter
Global shutter CMOS designs have existed for a number of years but none of them have appeared in stills cameras. The main challenge has been that the additional circuitry required for instant readout has taken up room in each pixel, limiting its dynamic range.
The a9 III uses a Stacked CMOS design which allows the circuitry and the photodiode to be moved into separate layers, alleviating some of this fight for space. However, it’s worth noting that the a9 III has a base ISO of 250, which suggests it has a lower full well capacity (less capacity for storing the charge generated during exposure). This reduced capacity for charge would mean the pixel clips earlier than conventional designs and hence is rated as having a higher base ISO.
However, if the higher base ISO is a result of reduced well capacity, rather than a major change in read noise, it won’t necessarily have any negative impact on high ISO performance. The added circuitry needed to provide a global shutter is also likely to mean this isn’t a dual gain sensor, since such designs also add to the circuit complexity. Sony Semiconductor has already introduced small sensors that separate the photodiode, the transistor and the readout circuitry, helping to further ease this DR restriction, but that doesn’t appear to be the case here.
The downside of the need to utilize a Stacked CMOS manufacturing process to make global shutter practicable. At present, the least expensive APS-C camera with a Stacked CMOS sensor is Fujifilm’s $2500 X-H2S, and the least expensive full-framer is Nikon’s $4000 Z8, so don’t expect this tech to trickle down to more modest models soon.
Bursts at up to 120fps
The a9 III’s most eye-catching spec is its ability to shoot at up to 120fps, and to pre-buffer up to one second’s worth of images from before you fully press the shutter. You can fine-tune how much of a pre-burst you want, from 1 second down to 0.1 seconds in 0.1 second increments, then down to 0.01 seconds in 0.01 second steps. There’s also a 0.05 second pre-burst option if you think you’re only missing your shot by the slightest fraction of a second.
If you prefer to use initiate AF with something other than the shutter button, you can choose whether to use this, a half-press of the shutter or both to start the pre-burst recording.
We’re told it can do this for 1.6 seconds even in 14-bit Raw, requiring a throughput of 6GB/s
Noticeably this is far beyond the maximum write rate of the CFexpress Type A cards used by the camera, so there’s clearly a large buffer within the camera. All modes are available with both CFe and SD cards, with different card types affecting how long the buffer takes to clear. It would seem to follow that the camera could clear its buffer twice as fast if Sony had used the more common CFexpress Type B cards, which have twice the read/write channels of Type A cards.
Video with zero distortion
The a9 III can shoot 4K at up to 120p without a crop. It doesn’t have enough pixels to capture 8K but will use all 6000 horizontal pixels for its 60p or slower footage.
As with stills, there will be no rolling shutter distortion or banding risk with the a9 III, making it ideal for shooting scenes with lots of movement. As with recent Sony models, it can capture 10-bit footage with up to 4:2:2 color subsampling.
Unlike the existing a9 models, the Mark III offers S-Log3 capture. As usual, the S-Log3 tone curve, designed to accommodate three additional stops of highlight capture, compared with standard color modes, means the base ISO jumps 3EV from 250 to 2000. The a9 III also offers the attractive S-Cinetone color mode (base ISO 320).
Ergonomics has long been an area of criticism of Sony, with the company generally making improvements, generation on generation. The a9 III continues this pattern with a significantly reworked hand grip. There’s a more pronounced bump at the top of the camera and a grip that encourages a slightly curved-in hand-hold, pushing your finger back towards the shutter button. The two custom buttons behind the shutter release are now raised, making them easier to reach.
We used the camera with the new 300mm F2.8 and other sizable lenses for several hours and found it to be the most comfortable Sony camera yet.
The a9 III uses the same 9.44M dot (2048 x 1536 pixel) viewfinder as the Sony a7R V, which offers a massive 0.9x magnification. By default, the screen refreshes at 120fps with no blackout during burst shooting. There’s also a 240fps refresh mode, but the resolution of the panel is reduced in this mode.
Interestingly, because the viewfinder and rear screen are still refreshed progressively, it can appear that the camera is exhibiting rolling shutter in some extreme conditions. If you examine the individual frames, all the verticals are straight: it’s just the refresh speed of the display panels (the rear LCD in particular) that gives the impression of slight distortion.
As you might expect, the a9 III includes all the subject recognition AF modes Sony has been developing in recent years. This means it has the ability to recognize humans, animals and birds, just animals, just birds, insects, cars and trains, and airplanes. You can limit which of these modes is available, just as you can limit the camera to just showing the AF area modes you like to use, and you get a choice over whether the camera highlights the recognized subjects it’s found in the scene.
The use of the latest Bionz XR processors and a dedicated chip for crunching the complex machine-learning-derived algorithms means the a9 III should outperform even the a1 in terms of subject tracking. Sony says the a9 III can recognize subjects when they’re half the size in the frame that the a9 II required.
Sony also says that because the a9 III provides such frequent updates of information to the processor, it represents the most effective instance of its subject recognition AF tracking yet.
As you might expect for a pro-targeted sports camera, Sony offers a battery grip for the a9 III. The VG-C5 displaces the battery in the camera body and has space for two NP-FZ100 batteries. It offers vertical orientation duplicates of the camera’s main controls, including a second C5 button, in reach of the middle finger as you operate the camera.
There are twin dials on the rear shoulder of the unit, with AF-On and AEL buttons and an AF joystick, all with the same layout and relative position to one another as on the camera’s body. Sony says the two batteries are treated as a single unit, used simultaneously, rather than individual batteries that are discharged in turn, which it says has allowed it to squeeze an additional 15% endurance out of the grip.
The a9 III is a fairly significant step forward for the a9 series: it brings all the upgrades we’d expect (the latest processing and high-res viewfinder from the a7R V) with one we didn’t: the adoption of a truly global shutter for the first time in a stills ILC.
The camera itself won’t be available for several months, yet, so we’ve been restricted to publishing JPEG images for now, but we’ll be looking at the camera’s image quality in more detail, the moment we can get a final production sample. In the meantime, we’ll be trying to work out all the things that a camera with no need for a progressive shutter (electronic or mechanical) will allow us to do.