Slide, pyramide entrance or grounding contact

The wonderful world of macro.
How close can you come with your lens. I've been using an analog 28mm lens with a reversing ring. The lens is therefore reversed the device.
This gives you a 50 mm at a magnification of 1: 1 (so if a normal macro lens), and at 20 mm, a magnification of 3.5: 1 to 28 mm, this will therefore about 3: 1. Thus, a magnification of 3X.

Here I have included a socket close. This is the contact of the grounding.
The distance between the front lens and the contact is about 2-3 cm.

Did you recognize it? Whether you thought it was the entrance to the pyramid of Giza or a slide?