Macro photography can be achieved by mounting a lens upside down on the standard mounted lens, it's an old trick, this technique is used to obtain high-quality macro images with high resolution and sharpness. Normally you simply screw a coupler adapter ring into the filter thread of both lenses. I use two Olympus OM Zuiko (35mm film) lenses, 28mm and 50mm, both lenses are 36 years old, but stored for over 33 years in a hall closet and they are still in absolute mint condition. Both lenses come with a 49mm filter thread, but unfortunately I don't have such an coupler adapter ring, so for one time only I linked both lenses together by means of a piece of duct tape to get this photo.
The magnification factor is calculated by dividing the focal length of the normally mounted lens by the focal length of the inverted lens, for example, when an 28mm lens is inverted mounted on a 50mm lens, the reproduction ratio is almost 2:1. I used nothing but the built-in camera flash and a piece of white paper as the reflective material. Adapters to connect filter threads of 2 lenses are made by several companies, I saw one today on the internet made by Caruba.