Dedicated cameras that can do this are widely available.

My (cheap, 15 year old) DSLR goes from “off” to capturing a photo in under 300ms. The battery essentially lasts indefinitely if you’re not actively fiddling with it. It will take about a thousand photos per charge, and changing the battery takes about 5 seconds.

> My phone can go from "off" (sleep) to taking pictures in less than a second with basically no effort

My Fujifilm X-E4 does the same? Flip the power switch, click the shutter. It's honestly identical in time to my smartphone - power on for these devices is crazy fast today IME

Right, no, obviously a dedicated device can power up faster than a general purpose computer. My point was that a general purpose computer can come out of sleep fast enough to be used in a camera, while maintaining acceptable tradeoffs in the process.

Ah right apologies, I misunderstood what you were saying. Yeah absolutely, though it does require the SoC for the "phone camera" to not be under-powered, which unfortunately for the attempts so far, they usually have been

Digital camera SoCs are actually multi-core ARM with a DSP on bus and tons of RAM, and actually do what GP proposes(boots up and goes to sleep when battery is inserted). Some runs Linux, some really obscure RTOS. Lots of SoCs are OEM'd, but no one talks who supplies who. All those cheap plastic looking body shells are paper thin cast magnesium in black paint, not even aluminum. Some has Peltier based active cooling for years.

The bunches of hackers behind those... they don't like talking to anyone on anything unless you're asking about marketed features on finished products, or you show a badge or a business card they recognize. So the Internet never knows.

That I'm actually aware of; I was talking about the Samsung Galaxy NX and the Yongnou YN455, both of which have kind of underpowered SoCs driving the android side of it, sadly. The YN455 less so, but still.