Sony Goes Global, Shutter That Is

bythom sony a9iiiangle

Today Sony announced the A9 Mark III model, with the big news being a new 24mp image sensor with global shutter capabilities. 

To understand the big news, you have to first understand the situation as it stood until today. The digital cameras we've been using all use what's called a rolling shutter. In a rolling shutter, data is captured and moved off the image sensor a few rows at a time. The time it takes in getting from the top of the frame to the bottom means that motion in the scene can result in distortion. 

In a camera such as the Sony A1 or the Nikon Z8/Z9, this rolling shutter is extremely fast, and that allowed Nikon, for instance, to completely remove the mechanical shutter. Removing mechanical things that can break is good for us, it makes cameras more reliable long term. It also means a camera can be made to be completely silent, which if you've ever been at a press conference with a dozen photojournalists clacking their shutters, you'd know to be a good thing ;~).

On the other hand, we have cameras with rather slow rolling shutters, too, such as the recent Nikon Zf. The reason why that camera still has a mechanical shutter is that the rolling shutter for the image sensor used would cause issues on motion. The difference between a rolling shutter and a global shutter is a bit like sitting in a theater: for a play, the curtain slowly rises to reveal the scene (rolling shutter) while for a movie the first scene instantly appears (global shutter). 

So why do we have rolling shutters, at all? Isn't the image sensor just a chip with "instant access"? One reason has to do with things that happen when you boost bandwidth (speed of transfers). It's partly the issue of how much data an image sensor is creating. You need extremely fast channels to get the data to the image processing chip, and the speed of electronics is one of those things that parallels Moore's Law: as semiconductor technology progresses, there are very predictable and real gains to be made, but nothing is instantaneous, even in digital.

Unfortunately, moving things really fast also has a tendency to induce read noise and thermal issues (and thermal issues can create noise of their own). There are also manufacturing and cost challenges that come into play, though as you're probably well aware, over time semiconductors solve those problems in subsequent generations. It's taken awhile for sensor makers to build affordable image sensors that get through all the possible issues, which is what Sony has done with the A9 Mark III.

What are the benefits of a global shutter?

  • No need for a mechanical shutter (simplifies build, improves long term reliability)
  • No motion artifacts seen in the frame
  • No stabilization motion artifacts
  • Potentially very high frame rates possible
  • Flash sync at any speed
  • Flicker free individual stills

The downsides are primarily going to be, at least initially, cost to produce, can produce more heat, and have higher noise than a sensor with the same design, but with rolling shutter.

Which brings us to the Sony A9 Mark III. The A9 Mark III features a 24mp stacked image sensor with a global shutter. This allows it to capture 120 fps (and 4K/120P). The viewfinder is blackout free, and Sony is claiming this is their fastest camera yet, with the best autofocus system they've deployed. 

Because next week is the 10 year anniversary of the full frame Alpha mirrorless line era, which started with the A7, it seems that the A9 Mark III was introduced now even though it's still quite a ways off from delivery. Sony says "Spring 2024". 

Besides the A9 Mark III, Sony introduced the 300mm f/2.8GM OSS, which Sony claims as the lightest 300mm f/2.8 available. Also available Spring 2024.

I've put up my usual data pages for the new products, but since actual final product delivery is a ways off, I'll reserve more comments until the product is actually delivered.

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