A person is tasked with creating a ray diagram to resolve the characteristics of the image of an object formed by a concave lens. The person has accurately drawn the principal axis of the lens, the plane of the lens the object a lens icon to specify the kind of lens and correctly drawn and labelled the focal points. Then the person illustrates the incoming ray shown. Which one of the subsequent statements about that ray is most correct?

The lens portray in the diagram is a concave lens a diverging lens. The specified ray would be a principal ray for a converging lens but such a ray is diverging from the principle axis of the lens as it approaches the lens and the diverging lens will cause it to diverge even more. By the plane of the lens the ray abruptly adopts a new path that makes a larger angle with the principle axis of the lens. We have no diagrammatic way of establishing the new path that is we do not know exactly where the light goes from there from the point at which it hits the plane of the lens) hence the ray in question is not a principle ray.

Note: The fact that the ray misses the "lens" does not rule it out as a principle ray. For one thing the lens depicted in a principal ray diagram is just an icon telling the reader what kind of lens is under investigation. It is not a scale size representation of the lens itself. Secondly it doesn't matter whether the principle ray goes through the lens or not (although it must pass through the plane of the lens).

The image produced by the rays that do pass through the lens will be in the same location that the principle rays predict whether or not the diameter of the lens is great enough for the principle rays to actually contribute to the image.