Light rays from objects behind the vehicle strike the mirror surface and reflect into the driver's eyes according to the law of reflection (angle of incidence equals angle of reflection), forming an upright, diminished virtual image.
Primarily convex mirror design: The mirror surface curves outward, causing light to diverge; this allows for a wider lateral field of view (approximately 120°–150°) within a compact size, though the image is reduced by about 15%–30%-hence the common warning label, "Objects in mirror are closer than they appear."
Some utilize dual-curvature mirrors: The inner flat section preserves an accurate sense of distance, while the outer convex section expands the field of view to cover blind spots, balancing accuracy with a wide-angle view.
While there is slight refraction at the glass-air interface (occurring during both incidence and exit), the primary mechanism for image formation is reflection; refraction is merely a secondary phenomenon resulting from the light path passing through the medium.
No lenses (convex or concave) are used: The rearview mirror is a reflective device; its operation is unrelated to the principles of lenses that focus or diverge transmitted light.