Which imaginary structures are used to describe refraction in lenses?

Principal planes are crucial in the study of lens behavior because they serve as reference points for how light rays are refracted when they pass through a lens. In the context of optics, a principal plane can be thought of as an imaginary plane where the bending of light occurs as it transits through a lens. These planes help to simplify complex lens systems into more manageable components, allowing for easier calculations and predictions about how the lens will affect incoming light.

When light rays enter a lens, they are refracted at the surfaces. The position of the principal planes allows for the determination of the lens's focal points and the overall optical power. By understanding where these planes are located in relation to the lens surfaces, opticians can accurately describe the lens's optical characteristics and how they influence image formation.

Other options do not accurately convey the specific concept of refraction in the context of lenses. Optical planes and light paths describe different aspects of optics, while refraction lines do not represent any defined imaginary structure within lens theory. Principal planes specifically address the geometry of lens refraction, making them the correct choice in this question.