After reading today's article about a
portable microscope for 11 thousand rubles, I remembered the existence of cheaper macro nozzles for the phone and drove into Google iphone micro lens. The search for pictures, in addition to a variety of factory products, gave this:

Yes, everything is really so simple, a drop of water on the lens works as a collecting lens and allows you to get a clear image of small objects! On the table I had an unfinished bottle of water, and in my pocket was an old fifth iPhone. Naturally, I decided to conduct an experiment.
First, I dropped water on the main camera, as shown in the photo above. But it turned out that a drop comes down if you try to turn the phone over. Then I put the phone face up, turned on the front camera and dripped water on the lens. The image of my face immediately became blurred, the selfie wouldn't work. But various small items with a distance of about a centimeter are visible perfectly. To make the image lighter, you can put a white piece of paper on the table next to it. Here is the first not very successful attempt - Lightning plug:
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Muddy spot at the top right - my forehead and hair.
I wear a silver chain, so I tried to photograph the very woman in the kokoshnik from the article about the microscope.

The result is so-so. In order not to smear the picture, you need to try to keep the object completely motionless. He made a bottle cap from a bottle cap and finally got a satisfactory result. Clicking opens the original GIMP with all EXIFs.

The stamp is bigger:
Vayngarten, with its microscope, had a similar mark on a gold product:

Let me remind you that the resolution of the front camera iPhone 5 - only 1280x960. With the main camera can get much better.
For those who want to repeat and also will water the front camera with water. Be careful not to fall into the speaker hole. The author is not responsible for accidental damage to smartphones readers.