Why does Sony's global shutter sensor have such a high (and weird) base ISO?

The Sony Exmor RS image sensor, against a plain background
(Image credit: James Artaius)

Sony has launched the world's first full-frame global shutter image sensor, which debuted in the Sony A9 III. However, lost in all the noise of the camera launch was a spec that went largely under the radar: this new sensor has a surprisingly high (and just plain unusual) base ISO of 250. 

In case you're asking what is a global shutter, a quick refresher: a conventional  rolling shutter sensor captures an image line by line, by scanning from left-to-right and top-to-bottom. This can create the rolling shutter effect of non-horizontal objects being distorted and warped. A global shutter sensor captures every pixel simultaneously, for faster and completely distortion-free imaging.

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CameraSensor typeFormatISO sensitivity
Nikon Z8 / Z945.7MP rolling shutter (stacked) Full frame64-25,600 (exp. 32-102,400)
Fujifilm GFX 100 II102MP rolling shutterMedium format80-12,800 (exp. 40-102,400)
Canon EOS R324.1MP rolling shutter (stacked)Full frame100-102,400 (exp. 50-204,800)
Sony A9 II24.2MP rolling shutter (stacked)Full frame100-51,200 (exp. 50-204,800)
Sony A7R V60MP rolling shutterFull frame100-32,000 (exp. 50-102,400)
Fujifilm X-H240MP rolling shutterAPS-C125-12800 (64-51,200)
OM System OM-120.4MP rolling shutter (stacked)Micro Four Thirds200-25,600 (exp. 80-102,400)
Sony A9 III24.6MP global shutterFull frame250-25,600 (exp.125-51,200)

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James Artaius

The editor of Digital Camera World, James has 21 years experience as a journalist and started working in the photographic industry in 2014 (as an assistant to Damian McGillicuddy, who succeeded David Bailey as Principal Photographer for Olympus). In this time he shot for clients like Aston Martin Racing, Elinchrom and L'Oréal, in addition to shooting campaigns and product testing for Olympus, and providing training for professionals. This has led him to being a go-to expert for camera and lens reviews, photo and lighting tutorials, as well as industry news, rumors and analysis for publications like Digital Camera MagazinePhotoPlus: The Canon MagazineN-Photo: The Nikon MagazineDigital Photographer and Professional Imagemaker, as well as hosting workshops and talks at The Photography Show. He also serves as a judge for the Red Bull Illume Photo Contest. An Olympus and Canon shooter, he has a wealth of knowledge on cameras of all makes – and a fondness for vintage lenses and instant cameras.