How to judge whether a lens is convex, concave or flat!

1. When irradiated with parallel light, it is a convex lens that can converge light, a flat mirror that does not change the optical path, and a concave lens that diverges the optical path.

2. When reading words with these lenses, convex lenses can be enlarged, flat mirrors of the same size, and smaller concave lenses.

3. Looking at the distance through the lens, it looks like a convex lens, the plane mirror remains the same, and the rest is a concave lens.