His optical work was important as well, where he is remembered for his observations of dark gaps in the solar spectrum (1802), a key event in the history of spectroscopy. He invented the camera lucida (1807) which contained the Wollaston prism (the four-sided optics of which were first described basically by Kepler) and the reflecting goniometer (1809). He also developed the first lens specifically for camera lens, called the meniscus lens, in 1812. The lens was designed to improve the image projected by the camera obscura. By changing the shape of the lens, Wollaston was able to project a flatter image, eliminating much of the distortion that was a problem with many of that day's biconvex lenses.