What is a camera
obscura?
The 'Camera Obscura' has a very long history and comes from the Latin meaning
quite literally 'Darkened Room' or 'Darkened Chamber'.
It developed out of the simple, lens-less 'pinhole camera' which was used,
perhaps a 1,000 years ago, to project an image of the sun and safely view
eclipses. The incorporation of a lens in the seventeenth century (or maybe
even earlier) produced a much brighter image and the camera obscura, as we
know it today, was born.
During the Victorian era many seaside resorts had a camera obscura which
was usually set up in a small octagonal building near the beach or on the
pier. Inside, the visitor could watch a moving colour picture of the view
outside.
Much used by solar astronomers and artists in the past, there is now a revival
of interest in camera obscuras. This website brings together information
about both the old camera obscuras, which once enthralled our grandparents,
and those that can still be visited today.
If you have any additional information about the camera obscuras included
on this website, or know of any others, please
let us know.
Also, to try and help you, a short glossary
of the technical optical terms used on this website has been put together.
How does a camera
obscura work?
The camera obscura is, in its simplest form, a lens
mounted vertically in an otherwise blocked out window. This will project
an image of the view outside onto an upright screen in a darkened room (camera
obscura is from the Latin and means 'darkened chamber'). However,
this simple type of camera obscura will only give a fixed view. If the lens
is placed horizontally in the roof, and an angled mirror placed above it,
it is then possible to rotate the optics and look around the building in
which the camera obscura is mounted.
The lens is obviously the key element in this type of equipment. The two
important attributes of the lens are its diameter and its focal length. The
focal length is simply the distance from the lens to the image when it is
in focus. The focal length of the lens governs the size that the image will
appear on the screen - a larger lens does not necessarily produce a larger
image although it may do so if it has a longer focal length. The brightness
of the image depends on the focal ratio. This is the number produced when
the focal length is divided by the lens diameter and is the ' F' number familiar
to photographers. The smaller this number is the brighter the image is although
the focusing becomes more critical. As with most optical equipment (e.g.
binoculars and photographic cameras) it is necessary to change the focus
to view things clearly at different distances and in camera obscuras this
is usually done by moving the screen either nearer to, or further from, the
lens.
The image produced by a simple camera obscura is always upside-down and laterally
transposed (i.e. a mirror image). When a mirror is introduced this transposition
is corrected, but as the optics above are turned through 360° the image
on the screen also turns full circle.
Most camera obscuras have a curved or bowl-shaped screen to match the shape
of the image and usually have a double or multiple lens. A single lens is
rather unsatisfactory as it splits up the white light into component colours
and this produces a poor image. A double lens with each component made out
of different types of glass and of different shape reduces this problem which
is known as chromatic aberration. The mirror in a camera obscura is flat
with a reflective coating on the front of the glass.
The heyday of the camera obscura was during the Victorian era although they
were invented over three-hundred year ago. Some of these old camera obscuras
still remain but many have been lost over the years. Recently, however, there
has been an upsurge in interest in camera obscuras with many new ones being
built and this website is an attempt to bring together all the available
information about those which still exist and a list of the now 'lost' camera
obscuras.
If you plan to visit any of the following camera obscuras please contact
them first to find out their opening times, entry prices, etc.
