real image

A real image forms when light rays traveling through or reflecting from an optical element actually converge and cross at a physical location in space. Unlike a virtual image, which appears to exist behind a mirror or lens but cannot be projected, a real image can be caught on a screen, sensor, or film placed at the convergence point. The rays must genuinely meet; the image is not a trick of perspective but a concentration of light energy.

Convex lenses and concave mirrors both produce real images under the right conditions. A convex lens creates a real, inverted image when the object is placed beyond its focal length; the distance from lens to image depends on the object distance and the lens's focal length, following the thin lens equation. A concave mirror likewise forms a real image when the object sits beyond the mirror's center of curvature, with the image appearing inverted and typically smaller. In both cases, the convergence point is on the opposite side of the optical element from the source.

Real images are fundamental to cameras, projectors, and telescopes. In a camera, the lens converges light onto a sensor or film plane where the image is actually recorded. In a projector, light passes through or reflects from a real image to cast it onto a distant screen. The position of the real image relative to the optical surface determines magnification and working distance, which shape the design of the entire instrument.

The term distinguishes this phenomenon from virtual images, which appear to exist but cannot be projected because no actual convergence occurs. A plane mirror creates only a virtual image; diverging lenses do the same. The difference is not academic: only a real image can expose photographic film or be captured by an electronic sensor without additional optics.

Real images require sufficient light intensity at the convergence point. In weak-light conditions, the image may exist geometrically but be too dim to detect or record. Aberrations in the lens or mirror can blur the convergence, spreading the light over a larger area rather than focusing it sharply, degrading image quality even though a real image technically still forms.