concave lens

convex lens

Convex lenses have a converging effect on light (also called converging lenses)

Concave lenses have a divergent effect on light (also called divergent lenses)

The light rays parallel to the main optical axis converge after passing through the convex lens (diverge after passing through the concave lens, and their reverse extension lines intersect) and the point on the main optical axis, represented by F

A convex lens has two real foci

A concave lens has two virtual foci

No change of heart

Parallel focus

over focus parallel

No change of heart

Parallel focus

over focus parallel

If the refracted ray is on the inside of the extension line of the incident ray, it is a convex lens.

If the refracted ray is outside the extension line of the incident ray, it is a concave lens.