Making a lens

In this case, we make a biconvex lens.
To do this, we cut out two convex blanks of the same shape from the “shoulder girdle” of the bottle. These blanks need to be glued together with plasticine, chewing gum or clay.. It is better to use the first 2 materials for gluing :-).
After gluing, it is necessary to completely fill the entire internal volume of the future lens with water (without bubbles).
It is better to fill the lens with water as shown in the figure. After filling the lens, it is sealed on all sides so that it does not leak and air does not pass inside.
The lens is ready. you can unload small text, work with small objects and start a fire.