Background information
How much resolution does a camera need?
by David Lee
6 Q&As on Sony’s global shutter
10/11/2023
Translation: Jessica Johnson-Ferguson
Sony has managed a technical breakthrough with its release of a camera with a global shutter. Get answers to six of the most pressing questions about this groundbreaking technology right here.
The Sony Alpha 9 III is causing a huge stir in the world of photography. Why? Because it’s the first full-frame CMOS camera to have a global shutter. So what does that entail? What does it do and what does it mean for the future? Here are the answers to the six most pressing questions.
1. What’s a global shutter?
It’s a process that reads all pixels of the camera sensor simultaneously. The term «shutter» is actually a bit of an outdated term, but it’s important to understand it.
Classic cameras have a mechanical focal plane shutter that opens and allows light to fall on an analogue film or digital sensor. It then closes again after a specified time. How? With the help of two shutter curtains, with the second one following the first. For fast shutter speeds, the focal plane shutter never fully exposes the entire sensor. What happens is that the second shutter curtain begins to cover the sensor again before that happens.
For SLR cameras with an optical viewfinder, the mirror must first be folded out of the way for this process. More recent camera models no longer need to do this, as they have an electronic viewfinder that takes the image directly from the sensor. This has paved the way for a different type of «shutter»: the electronic kind.
The new Sony Alpha 9 III is the first to do things completely different. The camera fully activates the sensor immediately and reads all pixels simultaneously – a genuine technological breakthrough.
2. What are the pros?
The global shutter eliminates several problems that other shutter systems struggle with. It also opens up new possibilities:
3. Who’s it for?
The advantages of the global shutter are particularly noticeable in three cases:
Apart from that, the global shutter will make a mechanical shutter superfluous in the future. This eliminates a complex component. Cameras could be designed to be more compact – and more affordable. However, the price reduction’s only likely to happen in the long term. Like any new technology, the global shutter will remain expensive for some years to come.
4. Can I really synchronise my flash with any shutter speed?
Here’s a little deep dive if you want to know exactly how long typical burn-off times are and what the specifications mean. If you don’t care, just scroll down to the next point.
The light intensity of a flash tube isn’t linear, but a curve that rises quickly and falls slowly. The stronger you set the flash to, the longer the burn-off time. It’s specified as T.5 or T.1. T.5 indicates the time that the flash shines at more than 50 per cent intensity. T.1 indicates the time it shines for at more than 10 per cent intensity.
T.1 is the relevant specification to estimate the shutter speed at which a global shutter no longer captures all the light. T.5 is misleading, because the flash has usually only emitted 60 per cent of its light at this point. Unfortunately, many manufacturers only specify T.5 because it looks better. Now that you’re armed with this knowledge, here are a few examples:
As you can see, the T.1 burn-off time of most flashes at full power is a good 1/300 of a second. Even if you accept a light loss of around 40 per cent, you’ll hardly achieve more than 1/1000 of a second. Faster shutter speeds only make sense if you don’t set the flash to full power – but then you have no additional advantage in the fight against the sun.
5. What are the cons?
A sensor with a global shutter requires an extremely large number of circuits in a very small space. After all, the signals from all pixels must be transmitted simultaneously. This is only possible in a stacked sensor, as the photodiodes and circuits aren’t arranged on the same level, but one behind the other. A conventional sensor probably wouldn’t have enough space for this.
Not to mention that it’s an expensive construction. This was already the case with regular stacked sensors. With an additional global shutter system, they’re even more difficult to manufacture. That explains why it took Sony so long to develop it. What’s more, the complexity of it could have a negative effect on image quality. Namely:
- less dynamic range
- more image noise
- lower resolution
Sony claims the global shutter in the Alpha 9 III doesn’t lead to poorer image quality. But this will only be verifiable with the final cameras and RAW images. In the first hands-on test with a pre-production model, I didn’t notice anything negative in terms of image noise or dynamic range.
The resolution of the Sony Alpha 9 III is a solid 24 megapixels – which is probably the limit of current production technology. More pixels would mean even more circuits.
6. What’s next for global shutter?
The next camera that would be suitable is the Canon EOS R1. It’s also a sports photography flagship. According to rumours, it will be launched in early 2024. Apart from Sony, Canon is the only manufacturer that builds its own sensors.
In practice, the rolling shutter effect is therefore only a problem in extreme situations. Similar to the stacked sensors of the Sony Alpha 1 (1/240 s) or the Nikon Z 8 (1/270 s). Unlike larger cameras, a smartphone will hardly ever be in a situation where distortion becomes visible. Usually, it wont’ have to synchronise with flashes either.
Header image: Samuel Buchmann
Samuel Buchmann
Senior Editor
Samuel.Buchmann@digitecgalaxus.chMy fingerprint often changes so drastically that my MacBook doesn't recognise it anymore. The reason? If I'm not clinging to a monitor or camera, I'm probably clinging to a rockface by the tips of my fingers.
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