Ray Diagrams for Lenses

Ever wondered how your eyes or a camera actually focus light? Ray diagrams show you exactly how lenses work by tracking light paths. There are two types of lenses: convex lenses (which curve outward like a magnifying glass) and concave lenses (which curve inward).

Drawing ray diagrams is dead simple once you know the two golden rules. First, draw a ray from your object parallel to the principal axis - after passing through the lens, this ray heads straight through the focal point. Second, draw another ray that goes from the object straight through the centre of the lens without bending.

Where these two rays meet is exactly where your image forms. The principal axis is just the horizontal line running through the middle of your lens, whilst the focal points are special spots where parallel rays converge after passing through the lens.

Quick Tip: Always use a ruler and draw your rays as straight lines - messy diagrams lead to wrong answers!