Water lens. View of a water lens projecting the inverted image of a candle onto a screen. The water lens is a spherical glass bowl filled with water. Since the glass and water are transparent, the bowl will act as a convex (or converging) lens. Light from the candle will refract when passing through the lens. The shape of the lens will cause the refracted light to converge at a focal point. It is here that the sharpest image is formed. The refraction causes the resulting image to be inverted. Equipment that use convex lenses (such as cinema projectors) have a means (often a second convex lens) to re-invert the image.