I got this iPhone 8+ yesterday and it’s very nice. It replaced a 3 year old 6+. It supposedly has two camera lenses on the back, one wide angle and the other “zoom telephoto” (which may simply mean one shorter and one longer focal length). And what used to be a round sapphire window over a single lens on the 6+ has been superseded by an oval window with two lenses behind it. However I am trying to understand how they work, and the first thing I tried was covering over one or the other lens while toggling the “1X” / “2X” zoom button on the camera.
Lo! Only one of the lenses is operating when I do this! It isn’t shifting between lenses when I hit that button.
The best description I have found “Apple and the future of photography in Depth: iPhone 8 Plus” at appleinsider.com but they don’t explain my observation. They also explain the new portrait mode, which gives several different options for photo style. This is more than just processing of an ordinary picture after taking it. The camera is using binocular vision to construct a depth map. In addition to R, G and B channels in the image there is also, in effect, a distance channel. The portrait modes uses this to blur or darken or brighten things that are more distant than the main subject which is taken to be the big close blob in the picture. This tries to mimic the effect of using a wide aperture, using a fill flash, or doing other things photographers with traditional full-control cameras do.
Still, I’d like to understand whether one of these is a longer focal length lens, or if one of them is indeed telephoto.
Also, “telephoto” has drifted in meaning over the decades. It used to mean that the rear principle plane of the lens assembly was actually in front of the body of the lens, so the lens is physically shorter than its focal length, whereas today it just means a long focal length… The opposite is a “retrofocus” lens, in which the front principle plane of the lens assembly is in back of the rear end of the lens body. That is, the physical structure of the lens is all further from the film (sensor) than its focal length. Now I wonder if “zoom” has drifted in meaning to mean “a long focal length”, from its earlier meaning of having a variable focal length. Are the two iPhone lenses of the same focal length or is one longer and the other shorter? And do one or both of them have the optical ability to change focal length?
Inquiring minds want to know!