Huawei's P30 Pro turned the zoom lens sideways to fit 5x optical zoom in a phone

Real optical zoom needs a row of lenses with room between them, and on cameras that can reach several feet. A phone lying face down must fit the display, sensor and lens into roughly 8mm of height, so most high-end phones in early 2019, such as the iPhone XS and Galaxy S10, offered only 2x optical zoom.

Huawei announced the P30 Pro on 26 March 2019 with a periscope design. After the lens cover, the light turns 90 degrees at a mirror, and the zoom lens elements and the CMOS sensor sit horizontally inside the phone. That uses the phone's length, not its thickness.

Ars Technica noted that Oppo had shown periscope prototypes, but the P30 Pro was the first commercial phone to ship one. The 5x telephoto is one of four rear cameras alongside a 40MP main, a 20MP wide-angle and a depth sensor.

Instead of squeezing a zoom lens into the phone's thickness, a mirror turns the light path sideways into the unused length.

Zoom needs distance between lens elements, and a phone has almost none in the thickness direction.

A mirror lets that distance run along the phone's length instead.

From outside the phone looks like it has a normal camera bump, just with a square opening.

When a dimension is the bottleneck, change the geometry of the system so the long part runs along the dimension you have in abundance.

The P30 Pro went on sale the day it was announced, starting at 999 euros ($1,125) according to Ars Technica. At launch it was the first commercial phone with a periscope zoom, a lead the article attributes to the sideways-lens trick.