I discovered this today... using an iPhone 8 running iOS 12.1 but I think this has been around awhile. Settings > General > Accessibility > Magnifier (Slide to ON) Then click the Home button 3 times and you can magnify, use the flash as a light and use the usual focus, snap a still shot then zoom, etc. Home button+lock button to take a screenshot (which made me shake it, but using it purely as a magnifier it looks surprisingly decent... better than I could show but being able to see an RPD on a half dime using a cell is good in my book.) Behaves differently than the camera...Had some filters to play with too. Not a bad substitute for a loupe in a pinch!