| 1 | Plane mirrors, convex lens and concave lens. | |
| 2 | He focused the sun's ray on a piece of paper with a burning-glass. | |
| 3 | The braiding yarns' section looks like a flat convex lens approximatively. | |
| 4 | In this paper, a measuring method of convex lens foci in collimator is given. | |
| 5 | Conclusion Wearing lower degree convex lens can reduce incidence rate of myopia in primary school students. |