What does 'do' signify in the context of lenses?

In the context of lenses, "do" signifies the distance from the lens to the object. This is an essential parameter in lens equations and optical calculations, as it helps to determine how the lens will manipulate light rays passing through it. Understanding this distance is crucial for predicting the characteristics of the image that will be formed, including its size and position.

When light rays emanate from an object, they travel towards the lens, and 'do' represents how far away that object is located from the lens itself. This distance aids in applying the thin lens formula, which relates the object distance, image distance, and the focal length of the lens. In practical terms, knowing 'do' allows students and practitioners to analyze and design optical systems effectively.