Florence Baptistery
According to his early biographers Giorgio Vasari and Antonio Manetti, Brunelleschi conducted a series of experiments between 1415 and 1420, including making paintings with correct perspective of the Florence Baptistery and the Palazzo Vecchio, seen obliquely from its northwest corner, as well as the buildings of Place San Giovanni. According to Manetti, he used a grid or set of crosshairs to copy the exact scene square by square, and produced a reverse image. The results were compositions with accurate perspective, as seen through a mirror. To compare the accuracy of his image with the real object, he made a small hole in his painting, and had an observer look through the back of his painting to observe the scene. A mirror was then raised, reflecting Brunelleschi's composition, and the observer saw the striking similarity between the reality and painting. Both panels have since been lost.