Al-Haytham: Water Magnifying Glass

This is a water magnifying lens, instead of a glass or plastic lens, i trapped water between two sheets of transparent food wrap.

When water fills the space between the two sheets it pushes the sheets to the sides and creates a curvature similar to the curvature of a glass lens, by increasing or decreasing the amount of water you can control the focal length of the lens.

I tried using sheets from transparent plastic bags but they tear when assembling the magnifying lens. food wrap was tear