Reflex mirror and other improvements
As remarkable as the instruments were, they didn't fully
satisfy the needs of artists. While canvas painting is a vertical
pursuit, many artists preferred to sketch a scene on a laptop
pad. In 1676, Johann Christoph Sturm, a professor of
mathematics at Altdorf University in Germany, introduced a
reflex mirror. Mounted at a 45 degree angle from the lens, the
mirror projected the image to a screen above. This elegant
configuration is at the core of modern single lens reflex
Design of a modern single lens reflex camera