Thin lenses
The key idea
A thin-lens model relates object distance, image distance and focal length. Converging and diverging lenses can form very different images depending on geometry.
Why it matters
Ray diagrams are not decoration: they encode the geometry that predicts where an image forms and whether it is real, virtual, upright or inverted.
A picture to remember
Ray diagrams are not decoration: they encode the geometry that predicts where an image forms and whether it is real, virtual, upright or inverted.