In fact, when the lens and the glass plate are irradiated with monochromatic light, some concentric rings with alternating light and dark can be observed. The distribution of rings is sparse in the middle and dense in the edges, and the center of the ring is at contact point O. The center of Newton's ring seen from reflected light is dark, while the center of Newton's ring seen from transmitted light is bright. If white light is incident, a colored ring will be observed. Newton's ring is a typical thin film interference with equal thickness. A circular wedge with uniform thickness is formed between the convex spherical surface of the convex lens and the glass plate. When the parallel light is perpendicular to the plano-convex lens, the two beams of light reflected from the upper surface and the lower surface of the wedge-shaped air film overlap each other, resulting in interference. The air film has the same thickness, and on the ring with the same radius, the optical path difference between the upper and lower surfaces is the same, so the interference pattern is circular. This kind of interference that produces the same interference fringes by thin films with the same thickness is called equal thickness interference. Newton's important discovery in optics is Newton's "Newton's Ring". This was put forward when he further investigated the color problem of the soap bubble film studied by Hooke.