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The OnePlus 7 Pro's telephoto lens isn't actually 3x optical zoom

OnePlus was quick to market its latest 7 Pro as having substantial photography improvements — it even danced around a National Geographic photographer at its launch event to talk about the cameras — but it turns out that some of the numbers tossed around in spec sheets while discussing the phone weren't quite right. That 3x telephoto lens included in the trifecta of cameras isn't actually providing a "3x optical zoom." In fact, it's closer to 2.2x, and it makes up for the difference in field of view by cropping.

Technically incorrect (the best kind). From the OnePlus 7 Pro specifications on OnePlus' site. 

How we know

The difference was discovered by /u/ImKuya over on Reddit, and OnePlus 7 Pro owners can actually test it for themselves. We know that the 7 Pro uses the telephoto lens for portrait mode (you can see that for yourself by switching over and covering up the bottom telephoto lens, the image is obstructed). But — and no one else including us noticed this — the FoV when in portrait mode is noticeably wider than in the 3x "zoom" mode, which also uses the telephoto lens.

Left: 3x "zoom" in normal Photo mode. Right: Portrait mode.

Both modes use the same lens and sensor, but somehow the image produced in Portrait mode is of a wider angle and at a higher resolution — 13MP in Portrait mode compared to 8MP in 3x "zoom" mode. So, in fact, the telephoto lens has a higher 13MP resolution, and it's actually cropping down to hit 3x.

Based on the math which describes the geometry of the situation, that crop places the actual optics of the telephoto lens around 2.2x rather than 3x (or 57mm instead of 78mm, in focal length and 35mm-equivalent terms).

What does this mean?

On the surface, the fact that it's reaching the 3x "zoom" field of view via a crop might not seem too bad, especially since this is just a crop. It's not like OnePlus is using your typical "digital zoom" where the image ends up being heavily processed to hit a higher megapixel rating — this is still effectively native, it's just cropping out the edges, sacrificing a bit of that potential 13MP maximum resolution down to 8MP to hit its target field of view. But, there's more to the optics and their resulting photos than just the apparent field of view. A higher "optical zoom" means a higher focal length, which also means different visual geometry in a scene — and you don't get the full "3x" OnePlus claims.

(The discussion is about to get technical, but we have a few photos that should make the subject easier to follow for non-shutterbugs.)

The effective difference between 2.2x and 3x "zoom" in 35mm-equivalent focal length for the sensor (i.e., what you'd see in a DSLR or mirrorless camera's numbers) has been calculated at ~57mm (2.2x) vs. the ~78mm (3x) focal length advertised. A 21mm difference might sound small as a number in isolation, but it's noticeable when it comes to photography. Things like the shape of a face or the relative angles of items in scene change quickly at lower focal lengths, and this is enough to make a visible difference. OnePlus 7 Pro customers aren't quite getting what they were told they would with "3x optical zoom."

Applied examples of focal length. Left: 80mm. Right: 56mm. Both cropped to the same relative size for demonstration. 

Focal length and "optical zoom" aren't just about the given field of view. Even if you crop them down to precisely the same angular view, the way they take in light is inherently different. I like to think of the scene as composed of a bunch of lines pointed at the camera that grow more parallel as the focal length gets longer, leading to things like wider faces, more visible ears, and tighter backgrounds, visible in the two examples above. (Thank my roommate for his saintly patience.)

via GIPHY

This difference in focal length isn't brought back on crop, either. It's a property of the optics being used, so cutting down the image won't make a difference or restore it, even if it can narrow the FoV slightly. (If you're familiar, think of crop factor when it comes to camera sensor types like APS-C or 4/3. A 50mm lens might crop down to 75mm, but you're still getting 50mm geometry.)

We've reached out to OnePlus for a statement as well as verification of the telephoto camera's specifications, but neither was forthcoming at the time of publication.

In the meantime, this discovery likely won't make a difference to the vast majority of 7 Pro owners. You get the full 8MP which OnePlus advertised, and it's technically "3x zoom," it's just not all optical, as OnePlus's site, specs, and marketing claim. But really, this discussion of focal length differences will go right over most heads. After all, OnePlus doesn't even market the optics in 35mm-equivalent focal lengths. However, any photography enthusiasts interested in picking up the OnePlus 7 Pro should keep in mind that they won't get the full ~78mm focal length that was seemingly advertised via the "3x optical" telephoto camera.

  • Thanks:
  • Matthew Stone

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