Animated model of the reflecting telescope designed and built by the English scientist Isaac Newton in 1671-2. Unlike earlier telescopes, which used lenses to focus light, Newton's designs used a concave mirror to focus light, helping to prevent the splitting of colours seen with lenses. This telescope was the third built by Newton, and had a mirror some 5 centimetres in diameter. Newtonian telescopes remain popular, as a large mirror is cheaper and lighter to construct than a lens giving the same light-gathering and magnifying power. Newton used his telescope to observe the phases of Venus and the moons of Jupiter. On black background. See clip K007 0020 for the same model on a transparent alpha channel.