Turns out the OnePlus 7 Pro`s telephoto lens can`t deliver 3x optical zoom
(Android Central)

The telephoto lens on the OnePlus 7 Pro only goes up to 2.2x optical zoom. What you need to know The OnePlus 7 Pro`s optical zoom is closer to 2.2x and not 3x. The telephoto lens is cropping 13MP photos down to 8MP to get to 3x zoom. Unlike the OnePlus 5, this isn`t digital zoom — you`re basically losing out on focal length. One of the marquee features on the OnePlus 7 Pro is the camera array at the back, where a 48MP primary camera is joined by an 8MP telephoto lens and a 16MP wide-angle lens. OnePlus advertises the telephoto lens with 3x optical zoom, but it turns out that`s not actually the case. As discovered by /u/ImKuya on Reddit, the telephoto lens doesn`t actually deliver 3x optical zoom, but closer to 2.2x. The OnePlus 7 Pro uses the telephoto lens for portrait shots, but the field of view is different when using portrait mode and 3x zoom. Turns out the sensor itself is a 13MP Samsung S5K3M5, and the telephoto lens is cropping 13MP photos down to 8MP to hit 3x zoom...