What Is 'Global Shutter'?

The New Sony top-of-the-line "fast" camera, the A9 Mark III or A9III, is here. It went up on B&H this morning ($6,000).

The camera is a technical tour-de-force, despite remaining surprisingly friendly to the hand and shoulder. The big news is that it has a 24-MP ~24x36mm (full-frame) global shutter, the largest global shutter yet made in any camera. A world first for Sony.

So what, exactly, is global shutter?

The familiar focal-plane shutters from half a century ago and more are mechanical shutters. They're easy enough to understand: a physical curtain blocks the image-forming light and is moved aside temporarily to allow image-forming light to reach the recording substrate. You probably know about many of the types as the form evolved, from rubberized cloth to titanium, eventually solving the high-shutter-speed problem by opening a smaller and smaller slit which traveled across the image; this is what caused distortion like Jacques Lartigue most famously used in his brilliant and beautiful photograph known as "The Racecar" (I saw a modern print of this at Kathleen Ewing Gallery in Washington, D.C. 30 years that remains memorable). It's also what caused the "flash sync" headache, because electronic flashes were of extremely short duration and could only register on the substrate if the entire shutter was open when it fired. So the flash sync speed was always slower than the highest possible shutter speed on a mechanical camera because it couldn't make use of the trick with the moving slit.

With CMOS digital sensors, electronic shutter became an option—instead of the sensor being physically blocked, photosites were turned on and off directly. However, the concept of the "moving [virtual] slit" persisted, because it was much easier to design and build a camera that registered a smaller amount of photosites, but to did so in succession. Starting from one side and progressing to the other like a scanner does. It meant the processor had less to do at once. This sometimes resulted in artifacts in the image that you might have seen: not only distortions with panning or camera movement, but banding, waviness, and other still and video effects known as "rolling shutter." These included wobble (a.k.a. the jello effect), skew, spatial aliasing, and temporal aliasing*. Some of the most pronounced (and bizarre) examples can be found in pictures of airplane propellers and helicopter rotors. These types of EVFs, along with mechanical shutters that use a traveling slit to effect high shutter speeds, are both known as rolling shutters.

A global shutter is simply an electronic shutter that captures the entire image all at once, instantaneously.

The advantages of this might seem obvious, but the details, in the case of the Sony A9III, are like science fiction—at least if you remember that I've been watching the digital transition for 35 years now (not with a front-row seat, but I've been in the audience). I remember when the word "megapixel" was a new and unfamiliar term; same with the first (futuristic!) 1-GB memory card. Development right along has been fast and furious....

Mike

*From the Wikipedia article "Rolling Shutter."

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Featured Comments from:

Joseph L. Kashi: "The immediate question is the top global shutter speed. With some current cameras, it is actually quite slow, on the order of 1/15 second with attendant subject motion blur. If Sony has been able to decrease the global speed to something on the order of 1/250 or so, that would be very useful."

Mike replies: The official A9III specs, per Sony, are as follows: "SHUTTER SPEED: Still images: 1/80000 [sic] to 30 s, Bulb. [...] FLASH SYNC SPEED: 1/80000 s, 1/500 s." There is a footnote after that "1/80000 s, 1/500 s" which reads, "With compatible Sony external flash." I have no idea what "1/80000 s, 1/500 s" as a flash sync speed could mean, and apparently Sony isn't sympathetic to my ignorance. It might mean 1/500th with mechanical shutter and 1/80,000th with electronic shutter, but...further digging required, because, as written, it doesn't make sense. We'll sort it out eventually.

David L.: "Sony has been making amazing developments on the camera SOC processor data speeds. The results are seen in very fast frame rates, high resolution video, and now a global shutter. Their ultra high speed electronics have a lot to do with these technological achievements."

Comments

[Jeff]

And now there are the early developments in image “content authentication,” starting with Leica M11-P, with other companies to follow.

[Stan B.]

Always thought it had some kind of major geopolitical connotations...

[Kye Wood]

Did you know that Aptina gave Sony their global shutter technology, in exchange for royalty free use of all of Sonys patents.

Aptina provided the sensor for the Nikon V1. An astonishing camera in its day.To my understanding, the first camera with a global shutter. Not long after its release, Sony came a calling on Aptina. Sony got the bargain of a lifetime.

[Allan Ostling]

I am wondering what one can do with flash sync at 1/80,000 second. Mosquito photography, perhaps, but what else?

[Kenneth Tanaka]

"...technical tour-de-force" is exactly what this full-frame global shutter camera is. While it might enable some variety of notable new general photographic results I see many new possibilities in the realm of sci-tech studies.

[Willem]

So here the last mechanical part that used to make up a camera is gone. A bit sad…

[John Krumm]

From what I understand the dynamic range might still be a problem. And Nikon is working on a hybrid global shutter design that can switch to classic rolling shutter for dynamic range benefits. Global shutter is one of those amazing advances that people have long pined for, but then, once it's here, I kind of feel a little underwhelmed for some reason. If I shot sports professionally I might think differently.

[Ned Bunnell]

As I looked at his print “Bullet through Jack of Hearts” this morning, I wondered what “Doc” Edgerton would think of this new global shutter.

https://flic.kr/p/2oKJznr

[Robert Roaldi]

To my limited knowledge, TV broadcast cameras haven't exhibited "rolling shutter", especially in sports coverage, since forever it seems. Did they use global shutters or did they resolve the problem in some other way?

I'm just asking because I'm wondering how much of a breakthrough this new camera is. Is it the case that the technology has reached consumer cameras at a "reasonable" price now?

[Most CCD sensors were/are global shutter. It's with CMOS sensors that it's rare (but not unknown). There are a variety of reasons cameras switched from CCD to CMOS, and now are almost all CMOS. I'll be covering this in Part II. --Mike]

[Dogman]

Like most recent innovations in camera technology:

I. Don't. Care.

Sorry, Sony.

[Mark Sampson]

In about 1992 or so, I had a few assignments to photograph some of Kodak's prototype digital SLRs. Of course I was using 4x5 film in the studio then... I wondered to myself "why can't they just turn the sensor on and off to make an exposure?" but with marketing types around, not engineers, I didn't speak up.
Thirty years later and it's here. Should be quite interesting to see what happens>

[Andy Kochanowski]

The rolling shutter was the reason I got rid of the Sigma View Camera you're so fond of, and rightly so. On people pictures, unless everything was still, it had a pronounced effect. Oh, and the 1/25 or so sync speed, I couldn't live with it.

Aside from my waning camera lust, the Sony seems like a solution in search of a problem.

[Dave]

After viewing some videos of the pre-production camera in action (on the B&H site), I have to say this is a major point in the camera timeline.

However, few will really need a camera with these specs.

You used to be able to buy a good used car at the price they're charging. (I know; get off my lawn.)

The high speed flash sync is of limited use right now. A full flash from a portable strobe unit isn't fast enough to take advantage of this camera.

Flash makers will have to come up with some new designs to get full power at such high shutter speeds. (Or just use continuous light.)

I agree with Thom Hogan that this announcement without availability for this holiday season smacks of "Don't buy anything else for Christmas. Wait (and save your money) for our camera."

Most of us won't need to consider such a camera. Our present gear suits most of us and takes very good photos.

Spending that kind of money for a trip abroad would probably make more lasting memories.

The buffer only holds ~1.5 sec at 120 frames per second, so you would still need to be fairly accurate when releasing the global shutter -- even with pre-release capture.

But if you've got money to burn, knock yourself out and let us know what you like and dislike about the actual camera.