The USB standard specifies a maximum of 5 meters (roughly 16' 5") I've used passive extenders out to 22ft and have daisy-chained active extenders out over 50 ft. The manufacturer of the active extensions we use claims that they work properly to 96 ft, but I don't know the basis of that as a maximum.
USB cable length when tethering a 5D in Capture 1?
in Mirrorless Digital Cameras
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