In this activity (posted on March 14, 2011), learners follow the steps to construct a camera projector to explore lenses and refraction. First, learners use relatively simple materials to construct the projector. Then, learners discover that lenses project images upside down and backwards. They explore this phenomenon by creating their own slides (must be drawn upside down and backwards to appear normally). Use this activity to also introduce learners to spherical aberration and chromatic aberration.