Refraction concave lens
For a concave lens, where light travels from a fast medium (e.g. air) to slow medium (e.g. glass), the light is bent towards the normal.
NOTE: See Mammoth Memory, Refraction, for how to use the term "FAST SOFA" to recall that, when going from a fast medium to a slow medium, the light bends towards the normal.
For a concave lens, when light travels from a slow to a fast medium, the light is bent away from the normal. See below:
NOTE: Again, see Mammoth Memory, Refraction and use the term "FAST SOFA" to mean, here, that when passing from a slow medium to a fast medium, the light bends away from the normal.
The overall impact of refraction on a ray of light is:
We can see that the light has been bent twice. In some books this diagram is summarised as:
But technically this is not correct.