iOS 10 had a feature that let you use the iPhone's camera as a magnifier, where is it in iOS 11?
iOS 10 added a useful feature that let you use your iPhone's camera as a magnifying glass, but buried it in the Accessibility settings. iOS 11 adds the magnifier to the Control Center, not only making it easily accessible, but bringing it to the public's attention as well. Head to Settings -> Control Center -> Customize Controls and add it to your Control Center, then you can access it from your CC. See here for tips on using it.