Museum
SM014
Magic Lantern circa
1930 Light
This is an apparatus, which
enables a magnified image of small objects to be projected on to a white
screen in a dark room. In
1634 the Englishman John Bate gave details of such a device.
Michael Faraday reinvented it in 1836.
A typical form is called a Sciopticon.
The source of light, usually a petroleum-burning lamp with flat
wicks is enclosed in a box having a chimney to provide a draught.
The box contains a concave mirror that redirects light going to the
rear thus reinforcing the front beam, while two plano-convex condensing
lenses concentrate the light on to the transparent object to be projected.
Two achromatic doublets spaced in a lens-tube comprise the
image-forming optics, which can be moved bodily for rough focusing and
with a screw adjustment for fine focusing.
The
Magic Lantern can project on to the screen physical experiments such as
the expansion of liquid in a thermometer and the deflection of the
gold-leaf electroscope. If
necessary, the inverted image can be righted by means of a right-angled
prism in front of the lens tube.
The
magnifying power of the Magic Lantern is calculated by dividing the
distance of the lens from the image by its distance from the object.
So, large magnifications are possible by using a lens of short
focal length.