It seems awkward to view an unsharp and inverted image. Can these problems be solved?
Both difficulties were solved soon after the invention of optics in the early 1600s. When a lens replaced the hole in the wall it produced across the room an image that was both brighter and sharper. However, the scene was still upside down. That problem was solved by arranging the lens to look vertically upward into a flat mirror held at about 45° to the optical axis. Now the image is projected down onto a horizontal white table where the scene will appear right side up if the viewer stands with his back to the outside area of interest. Early lenses were single pieces of glass that produced a greatly improved image but one that still suffered from color fringes around bright objects an increasing unsharpness° toward the edge of the viewing table. A camera obscura today uses a lens with two or more glass elements that reduce these problems. Four hundred years ago, the flat mirror was simply a polished metal plate. About 1850, opticians learned how to apply a shiny silver film to a poli
