So yes extremely fast even with today's technologies.
> After "tinker[ing] with different combinations of lenses and film stock," the production obtained three super-fast 50mm lenses (Carl Zeiss Planar 50mm f/0.7) developed by Zeiss for use by NASA in the Apollo Moon landings, which Kubrick had discovered. These super-fast lenses "with their huge aperture (the film actually features the lowest f-stop in film history) and fixed focal length" were problematic to mount, and were extensively modified into three versions by Cinema Products Corp. for Kubrick to gain a wider angle of view, with input from optics expert Richard Vetter of Todd-AO. The rear element of the lens had to be 2.5 mm away from the film plane, requiring special modification to the rotating camera shutter.
https://en.wikipedia.org/wiki/Barry_Lyndon
> The lens was designed and made specifically for the NASA Apollo lunar program to capture the far side of the Moon in 1966.
> In total there were only 10 lenses made. One was kept by Carl Zeiss, six were sold to NASA, and three were sold to Kubrick.
But to me the important question is if it has any impact on the number of lights. If you still need all the same lights to use the iPhone that you would for a camera that is several thousand dollars. it is still really cool.
People forget how much more sensitive silicon is to light than film.
I can recommend watching the Better Call Saul DVD documentary, they regularly have the lead lighting guy answering questions in there. The tl;dr was to me that yes, you definetely need additional lighting, even if your camera has a massive, light sensitive sensor.
I don't think anyone expects an iPhone to compete with a top of the line Arri 65 or other IMAX enabled cameras when it comes to low light performance (the sensor on these is huge after all), but the intro shot with Apple Park shows that it's possible.
Maybe don't try to reenact a shooting of Barry Lyndon on an iPhone, but for nearly everything else it seems to work just fine.