The iPhone 11 Pro phones come with triple 12MP Ultra Wide, Wide, and Telephoto cameras. The iPhone focal length of the lenses are 1.54mm, 4.25mm and 6mm. Their 35mm equivalent focal lengths are 13mm, 26mm, and 52mm, respectively. Cinematographer Newton Thomas Sigel gives a great explanation of the different effects of wide, normal and telephoto lenses.
In the late 1970’s, I used the Nikon 13mm f5.6 lens on the Nikon F2 camera. The Nikon 13mm lens had a 118 degree angle of view and in its time, it was remarkable in that it was a rectilinear lens. The extreme angle of view opened up new creative possibilities in all types of photography including indoor, architectural and landscape photography.
The iPhone 11 Pro’s Ultra Wide camera angle of view is 120 degrees. When using the Wide and Telephoto cameras with iOS 13.1 camera app, the Ultra Wide lens enables a preview of what is outside the frame. This outside the frame information is also captured in the Wide and Telephoto cameras to enable post processing cropping without losing image information. This setting can be enabled in Settings -> Camera -> Photos Capture Outside the Frame.