Light of different colors travels at different speeds in different materials and structures. This is why we see white light split into its constituent colors after refracting through a prism, a phenomenon called dispersion. An ordinary lens cannot focus light of different colors to a single spot due to dispersion. This means different colors are never in focus at the same time, and so an image formed by such a simple lens is inevitably blurred. Conventional imaging systems solve this problem by stacking multiple lenses, but this solution comes at the cost of increased complexity and weight.