A tool for looking
Once people understood how a dark room could project the outside world, it became a tool as well as a curiosity. This article follows the device through the two groups that depended on it most: painters, who used it to study how a scene looks flattened onto a surface, and astronomers, who used it to look at the sun without damaging their eyes. It also covers how the machine shrank into portable forms. The underlying optics are explained in a separate article.
The Renaissance recommendation
Around 1500, notebooks attributed to Leonardo da Vinci describe the principle, including the point that the image is inverted. Books printed with movable type spread the idea. In his 1558 book Natural Magic, the Neapolitan writer Giambattista della Porta described the camera obscura as an entertainment and as an aid to drawing. He suggested that someone could trace the projected image of a scene, even a hunting scene or a battle acted out outside the room, and that a person without drawing skills could produce a likeness. Della Porta’s claims about his originality have been questioned, since earlier writers had described much of the same thing.
A few years later, in 1568, Daniel Barbaro, a Venetian scholar, recommended fitting a lens and a movable disc with a small hole to sharpen the image. The combination of lens and adjustable aperture made the camera obscura much more useful for artists, and lens making was advancing quickly at the time through work on the telescope and the compound microscope. Artists traced the projected outlines with graphite pencils or with iron gall ink on thin paper.
The astronomers
Astronomers used the device for solar observation well before artists made much of it. In 1544, Gemma Frisius published an illustration of a camera obscura used to watch a solar eclipse. The Danish astronomer Tycho Brahe is also reported to have used pinhole methods to measure eclipses. Johannes Kepler used them extensively and applied the Latin term camera obscura in his 1604 writing on optics. He also made a portable tent version for sketching landscapes.
Projection became a standard way to study sunspots. Observers could project the sun’s image from a telescope onto a screen and trace the spots without staring into the sun. Christoph Scheiner and Galileo both used projection methods in the early 1600s, in a dispute over priority and interpretation. That method remains a standard safe way to observe the sun, although a direct view through any optical instrument without proper filters is dangerous.
Making it portable
Large rooms were impractical for traveling artists. Over the seventeenth century, inventors designed tent-like enclosures and boxes that were small enough to carry. The key problem was getting an upright image. A mirror set at 45 degrees inside the box could reflect the image upward onto a ground-glass screen at the top, where it could be traced with thin paper. A design published by the German monk Johann Zahn in 1685 used this arrangement, with a lens that could be focused by sliding a tube. Mirror boxes of this kind were manufactured in many sizes, some shaped like books, and became familiar to amateurs and professionals by the eighteenth century. The English painter Joshua Reynolds is known to have owned one disguised as a book.
Did the old masters use it?
This is the most debated question. Some art historians argue that painters such as Canaletto, who painted views of Venice, used a camera obscura to establish the main outlines of his cityscapes, and an optical device associated with him is on display in Venice. For the Dutch painter Johannes Vermeer, the evidence is more indirect: the way highlights are rendered and the apparent perspective of some paintings have led to suggestions that he may have used one. In 2001, the painter David Hockney and the physicist Charles Falco proposed in their book Secret Knowledge that many artists used optical aids from about 1420 onward. The proposal attracted both interest and strong criticism. Critics point to the lack of documents showing such use, and note that skilled painters could produce the same effects by observation. There is no consensus, and no record that settles the question for Vermeer.
Related tools
The camera lucida, patented by the English scientist William Hyde Wollaston in 1807, is a different device. It used a small prism to let the artist see the scene and the paper at once, with no darkened space. It was lighter and easier to use outdoors, and it became popular for sketching. The camera obscura, however, remained the instrument that led directly to photography, since its screen could be replaced with a light-sensitive material.
Decline and legacy
When photography arrived in 1839, the camera obscura lost its main role as a drawing aid. Painters moved to photographs as references, which in turn raised new debates about copying from images. The dark room survived as a tourist attraction and teaching aid, and its main function lives on in every lens-based camera.
What is documented
Written descriptions by della Porta, Barbaro, Kepler and Zahn are well documented, and so are astronomical uses from the 1500s. Claims about particular painters range from reasonably supported to speculative, and any statement that a famous artist definitely traced from an optical device should be treated with caution.