AstroMedia Hands-on Science Series Инструкции по строительству - Страница 3
Просмотреть онлайн или скачать pdf Инструкции по строительству для Игрушка AstroMedia Hands-on Science Series. AstroMedia Hands-on Science Series 12 страниц. Camera obscura
Печатать страницуThe Camera Obscura
The Mother of all Cameras
The principle of the camera obscura (dark room), the
forerunner of all our photographic and video devices, is
amazingly simple: in a darkened room, a small hole in a
wall creates an upside-down image of the outside world
on the opposite wall.
The picture isn't very bright because the small amount of
light that comes through the hole is spread over the en-
tire wall, but once your eyes adjust to the darkness, the
picture magically becomes visible. The camera obscura
can be a whole room or just a box where the projection
screen is replaced by a transparent screen so that the im-
age can be viewed from the outside (see sketch).
One might assume that even prehistoric people ob-
served that a small hole in the curtain in front of the cave
opening projects the landscape into the interior. The
camera obscura would therefore be the oldest optical
device known to mankind.
Aristotle (384-332 BC) was the first to study it scien-
tifically and Leonardo da Vinci discovered that it copies
the optical principle of our eyes (and the ones of most
vertebrates). In fact, the image on the retina of the eye
is upside down! That we see it the right way up is due to
corrective action in our brain. The pinhole camera, as the
camera obscura is also called when it does not use a lens,
is subject to two laws:
1. The further away the projection screen is from the pin-
hole, the larger and dimmer the image will be.
2. The larger the pinhole, the brighter the image will be,
but also the more blurred it gets.
This severely restricted the possible uses of the camera
obscura, e.g. to the observation of very bright objects
such as the Sun during solar eclipses. The problem was
not solved until the 16th century, when for the first time
ground glass lenses replaced the simple pinhole. They
admitted more light and made it possible to sharpen
(focus) the image.
But a focusing camera obscura has a different disadvan-
tage: the lens cannot focus on objects at different dis-
tances at the same time. It has to be pulled out to focus
on close objects and pushed in for objects that are fur-
ther away. A pinhole camera, on the other hand, focuses
on all points of the image equally.
In 1686, Johann Zahn constructed the first camera ob-
scura which, with the help of a mirror, allowed the ob-
served picture to be traced with a pen on a screen. As a
result, it became popular with painters, who could use it
to easily determine the perspective for their paintings.
The almost photorealistic views of Dresden by the Vene-
tian painter Canaletto from around 1750 are well known.
He used a focusing camera obscura to create them. This
AstroMedia kit works exactly like the camera he used.
In 1826 photography was born when the Frenchman
Nicéphore Nièpce shortened the imaging process by
capturing the picture directly on a light-sensitive plate.
The camera obscura lives on today in the millions of pho-
to and video cameras and, of course, in the miniature
cameras of mobile phones.
However, there are still real camera obscuras in operation
at some tourist attractions (e.g. on the Royal Mile in Edin-
burgh): a large, darkened room in which the outside world
is projected onto a table via a mirror in the roof and so can
be viewed by entire groups at the same time.
This kit contains:
• 4 die-cut sheets of cardboard, 0.65 mm thick
• 4 die-cut sheets of cardboard, 0.4 mm thick
• 1 acrylic glass lens Ø 62 mm, focal length +275 mm
• 1 acrylic glass mirror, 188.5 x 188.5 x 2 mm
• 1 clear viewing screen made of transparent hard
plastic, 190 x 190 mm
• 1 optional diaphragm to cut out
• 3 pieces of tracing paper, 160 x 160 mm
• 1 title page and these building instructions
A detailed photograpic instruction
by Michael Monscheuer can be
found here:
astromedia.de/pdf/
COB-E_Camera_Obscura_BB.pdf