I'm confused about the use of the term "zoom" in much of the discussion about the iPhone 7 Plus. As near as I can tell, just as has been the case on all previous models, there's no optical zoom at all. There's the usual digital zoom (cropping) and what's been added a second lens with a longer focal length, that is switched to (under favorable conditions) when the zoom level goes over 2x. So what's really going on is an automated switch from one lens to the other as cropping passes the 2x mark. Is that what's going on, or am I missing something?
Apple states the iPhone 7 Plus has "optical zoom at 2x" and digital zoom up to 10x (versus the iPhone 7 having digital zoom only, and up to 5x).
From developer notes:
These two cameras [can operate as] as a single virtual camera that automatically switches between physical cameras for zoom — in effect turning two prime lens cameras into a single zoom lens camera.
The Dual camera's defining feature is its ability to smoothly transition between wide and tele cameras, acting like a single lens camera with optical zoom at 2x.
The point at which the cross over from wide-angle to telephoto happens depends on a variety of factors including current focus position, current zoom factor, and current exposure.
From a developer's point of view, when accessing the cameras, they can choose to target one of the two cameras specifically or can access a hybrid "virtual" camera that automatically switches as the user zooms.
Apple is not necessarily incorrect when it states that 2x is optical zoom, since at that point the image is entirely "zoomed" through physical lenses and not in software. That said, there is no lens on the device that is independently capable of optical zoom, so the term is also not really being used in its traditional meaning.
Beyond 2x, zoom is entirely digital.