At optical infinity, light rays are considered to be which of the following?

At optical infinity, light rays are considered to be which of the following?

• A. Converging
• B. Diverging
• C. Refracted
• D. Parallel

Answer: (D)

Light from an object at optical infinity is treated as a set of parallel rays. Because the object is so far away, the rays arriving toward the eye (or a lens) travel in essentially the same direction, forming a collimated beam. This is why a lens will focus parallel rays to its focal point, and why the eye is relaxed when looking at distant objects—the incoming light is effectively parallel. Diverging or converging describes rays spreading apart or coming together, which isn’t the defining behavior at optical infinity, and refracted refers to bending at a medium boundary rather than the directional relation of rays from a distant object.

Light from an object at optical infinity is treated as a set of parallel rays. Because the object is so far away, the rays arriving toward the eye (or a lens) travel in essentially the same direction, forming a collimated beam. This is why a lens will focus parallel rays to its focal point, and why the eye is relaxed when looking at distant objects—the incoming light is effectively parallel. Diverging or converging describes rays spreading apart or coming together, which isn’t the defining behavior at optical infinity, and refracted refers to bending at a medium boundary rather than the directional relation of rays from a distant object.