The OnePlus 7 Pro's 3x zoom isn't misleading, just confusing

Update 2: So it looks like a lot of us got caught up in the semantics of what it means when a phone has "optical" zoom on a smartphone. Of course, it's not the same as having a true optical lens that moves along a focal plain; phone sensors interact with lenses of fixed focal lengths, and when we extrapolate those focal lengths we confer meaning by using a 35mm sensor-size equivalent.

In this case, OnePlus is using a 13MP sensor for its telephoto camera but when zoomed at 3x it only uses 8 megapixels of resolution, allowing a great crop factor without losing detail. Basically, yes: the 13MP sensor has a 2.2x equivalent focal length which, when cropped to 8MP, is 3x.

Juan Carlos Bagnell of SomeGadgetGuy has a very detailed writeup of this phenomenon which isn't unique to the OnePlus 7 Pro. It's just a little confusing because we write about optical zoom on phones the same way we write about it on proper cameras with moving components. Because of the tiny size of the sensors and very narrow lenses, zoom on phones relies largely on compromises between sensor size and distance from the lens.

While the original article is below for transparency, Android Central regrets the error.

-Daniel Bader, Managing Editor

Update 1: In a statement to Android Central, OnePlus has clarified that the 3x zoom is "lossless." Notice the distinct lack of references to 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. As noted by our friends over at Android Police, OnePlus is effectively cropping the edges to hit the zoom target, and in doing so you lose out on the field of view.

OnePlus advertises the telephoto lens with a 78mm focal length, and that's in line with what you'd expect from a 3x optical zoom lens. But because the sensor is cropping down to 8MP, the effective focal length is 57mm, or a zoom factor of 2.2x.

This isn't the first time OnePlus was caught misleading when it comes to the camera on its devices. The manufacturer had to walk back claims of 2x optical zoom on the OnePlus 5 after it was found that the phone was only capable of 1.6x zoom. OnePlus clarified after the fact that the remaining 0.4x was achieved via digital zoom:

The company isn't using digital zoom in this scenario, but it isn't delivering full 3x optical zoom either. Guess it's time to update the marketing materials.