The dual lens system on the iPhone 7 Plus is a pretty useful feature — you get the benefits of an 2X optical zoom whenever iOS decides it’s appropriate — but unfortunately due to the differences between the two lenses in both aperture and physical position, this can cause a “glitch” in your video if your iPhone switches to or from the second lens as you’re zooming in or out. The good news is that Apple has tucked away a setting that will allow you to avoid this problem by preventing the iPhone from automatically switching lenses during video recording.
The setting is called “Lock Camera Lens” and you can find it in the Photos & Camera section of the iOS Settings app, under Record Video. This setting only takes effect when you’re actually recording a video, and when enabled, the iPhone will keep on using whichever lens you started recording with. This means that in most cases you’ll simply be relying on digital zoom rather than optical, however if you begin recording a video while zoomed in to beyond 2X, you may not be able to zoom back out, as you’ll already be using the 2X lens. Keep in mind, however, that there are a number of factors that iOS uses to determine whether it should use the optical 2X lens or simply rely on digital zoom, such as in lower light conditions where the faster primary lens has an advantage, so you won’t always see the impact of the “Lock Camera Lens” setting, but at least you’ll be comfortable knowing that you won’t accidentally run into any jarring transitions while recording video on your iPhone 7 Plus.