There's a particularly interesting new Accessibility setting in iOS 10 that lets you mega-zoom into objects using your iPhone's camera. Yes, I know... you can just "pinch" to zoom in the Camera app, but what I'm talking about goes beyond this traditional camera zoom.
The feature is called Magnifier, and can be enabled by going into Settings -> General -> Accessibility -> Magnifier and toggling it on. Oddly enough, you can't enable or disable this feature from the Accessibility Shortcut menu (which is similar to how Guided Access works).
After that, all you need to do is triple-click your home button from any screen (except the lock screen, of course) to bring up the Magnifier app. If you already use your triple-click shortcut for Guided Access or another Accessibility Shortcut such as VoiceOver or AssistiveTouch, a menu will pop up asking you to select which shortcut to use.
As you can see below, Magnifier can zoom in much farther than the stock Camera app can. Despite the new iPhone 7 Plus having a telephoto lens, the max zoom is very similar to older iPhones because Magnifier uses the regular wide-angle lens since it can focus better at closer ranges (see bottom of this article to see how the 7 Plus performs against the 6 Plus).
Besides zooming, there are plenty of different options to choose from to help you see what you're looking at better. You can press the lightning bolt icon to turn on the flash (which will stay on until you turn it off or exit the Magnifier app), lock and unlock exposure by tapping on the focal point or the lock icon, and adjust brightness and contrast by hitting the filter icon.
In the filter app, you can choose no filter, white/blue, yellow/blue, grayscale, yellow/black, or red black.
You can also tap the inverted icon in the bottom left for inverted, blue/white, blue/yellow, inverted grayscale, black/yellow, or black red views.
Once you have it how you want it, you can press the shutter button to take a photo. It won't go to your Camera Roll, and will only reside in the Magnifier app until you press the shutter icon again, in which case you start over. However, you can take screenshots which you can access later like any other screenshot.
You can also touch on the preview image to bring up the zoom controls again, in which case you can zoom in and out of your static image.
In a side-by-side comparison of the iPhone 7 Plus and iPhone 6 Plus, you can see that the iPhone 7 Plus definitely has a sharper image, though it doesn't seem to zoom in quite as much as the iPhone 6 Plus did—which is probably a good thing, to prevent too many details being lost.