Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: The focal length , , of a lens or mirror is the distance from the surface of the lens or mirror to the place where the light is focused. This is called the focal point or focus . For diverging lenses or mirrors, the focal length is negative. Answer: diverging
What type of lens and mirrors have a negative focal length?