A convex lens gathers light to a focus; a concave lens spreads it out. Drag the sliders below to switch the lens type and change the focal length, object distance and object height, watching real and virtual images form via 1/v = 1/f + 1/u.
Your two lenses do opposite things to the same rays. A convex lens is converging: it pulls incoming light toward a single focus. A concave lens is diverging: it fans the same light outward. That one difference decides every image you can form. Flip the lens-type toggle and watch the traced rays swing from meeting to splaying apart while the readouts recompute the outcome.
The simulation solves the thin-lens equation in the form it displays, 1/v = 1/f + 1/u, giving the image distance v and the magnification m = v/u. Convex lenses carry a positive f; concave lenses a negative one. Drag Object distance across a convex lens and the image jumps between two lives: a far object yields a real, inverted image that could land on a screen, while an object tucked inside the focal length yields a virtual, upright, magnified one — the magnifying glass in your hand.
A concave lens refuses that drama. Slide the object anywhere and it stays virtual, upright, and diminished, its rays only appearing to diverge from a point you cannot project. Real images meet; virtual ones merely seem to. Only the converging lens can enlarge; the diverging one always shrinks — confirm each rule by reading m as you go. Push the same numbers through the lens and mirror calculator, then open more optics playgrounds.
A convex lens is converging: it is thicker in the middle and bends parallel light to a focus. A concave lens is diverging: it is thinner in the middle and spreads light outward. A convex lens has a positive focal length, a concave lens a negative one.
It depends on the object distance. An object beyond the focal length gives a real, inverted image that can be projected on a screen. An object inside the focal length gives a virtual, upright, magnified image — the magnifying-glass effect.
Always a virtual, upright, diminished image, at any object distance. A diverging lens cannot form a real image of an ordinary object, so it always makes the object look smaller.
A real image forms where light rays actually meet, so it can be caught on a screen and is inverted. A virtual image forms where rays only appear to come from, so it cannot be projected and is upright.