On the Pro models, Apple has implemented a similar scheme for three other increments of the main camera. Tapping the ‘1x’ button cycles among three zoom levels, which Apple has also marked as photographer-friendly millimeter equivalents: 24mm (1x), 28mm (1.2x) and 35mm (1.5x).
It’s tempting to think these increments are additional crops to the 48MP sensor, the way the 2x zoom is, but on Apple’s iPhone 15 Pro product page, it specifically says, “That’s the power of computational photography.” The camera system appears to be capturing a specific range of the sensor, and then processing with Photonic Engine and other ML technologies in its pipeline.