n in
1620 we learn that Kepler had made himself a portable dark tent fitted
with a telescope lens and used for sketching landscapes. Further, he
extended the work of Maurolycus, and demonstrated the exact analogy
between the eye and the camera and the arrangement by which an inverted
image is produced on the retina.

In 1609 the telescope came into use, and the danger of observing the sun
with it was soon discovered. In 1611 Johann Fabricius published his
observations of sun-spots and describes how he and his father fell back
upon the old method of projecting the sun's image in a darkened room,
finding that they could observe the spots just as well as with the
telescope. They do not seem to have used a lens, or thought of using the
telescope for projecting an enlarged imase on Kepler's principle. This
was done in 1612 by Christoph Schemer, who fully described his method
of solar observation in the _Rosa Ursina_ (1630), demonstrating very
clearly and practically the advantages and disadvantages of using the
camera, without a lens, with a single convex lens, and with a telescopic
combination of convex object-glass and concave enlarging lens, the last
arrangement being mounted with an adjustable screen or tablet on an
equatorial stand. Most of the earlier astronomical work was done in a
darkened room, but here we first find the dark chamber constructed of
wooden rods covered with cloth or paper, and used separately to screen
the observing-tablet.

Various writers on optics in the 17th century discussed the principle of
the simple dark chamber alone and with single or compound lenses, among
them Jean Tarde (_Les Astres de Borbon_, 1623); Descartes, the pupil of
Kepler (_Dioptrique_, 1637); Bettinus (_Apiaria_, 1645); A. Kircher
(_Ars Magna Lucis et Umbrae_, 1646); J. Hevelius (_Selenographia_,
1647); Schott (_Magia Universalis Naturae et Artis_, 1674); C.F.M.
Deschales (_Cursus, seu Mundus Mathematicus_, 1674); Z. Traber (_Nervus
Opticus_, 1675), but their accounts are generally more interesting
theoretically than as recording progress in the practical use and
development of the instrument.

The earliest mention of the camera obscura in England is probably in
Francis Bacon's _De Augmentis Scientiarum_, but it is only as an
illustration of the projected images showing better on a white screen
than on a black one. Sir H. Wotton's letter of 1620, already noted, was
not published till 1651 (_Reliquiae Wottonianae_, p. 141),