Volltext: Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine

This «apparatus is-designed for all kinds of projection, and with the objects 
cither in a vertical or in a horizontal position. When the object is in a vertical 
position the illuminating device (arc lamp with parabolic reflector) sends the 
light horizontally through the specimen, apparatus and to the screen as would 
be the case in the figure here shown. 
If the object is in a horizontal position the lamp and reflector remain in a 
horizontal position and the light is reflected by a mirror upon the opaque 
object ; or for vertical opaque objects the radiant is turned sidewise. 
For transparencies in a horizontal position the lamp and reflector are lowered 
to the level of one of the mirrors below, and this mirror reflects the horizontal 
beam up through the transparent object whence it passes to the projector and 
the screen. 
The entire apparatus is covered by a dark curtain (compare fig. 95). 
Use of Opaque Projection for Exhibitions and for 
§ 283. Testing the lantern.—The directions given in Chapter I, 
§26 are applicable here. 
§ 284. Size of objects for opaque projection.—The size of 
object which can be shown with an opaque projector varies greatly. 
The smallest size is usually larger than a lantern slide. The lan¬ 
tern-slide opening is rarely greater than 6.5 x 7.5 cm. (2.6 x 3 in.), 
while the smallest picture usually shown in the opaque lantern is 
rarely less than postal card size (8 x 12.5 cm., 3x5 in.). From 
this minimum the size ranges all the way up to 50 cm. (20 in.) 
Of course the radiant and condenser must vary accordingly 
(see fig. 107). 
§ 285. Objects for opaque projection.—The best of all are dull 
white objects, like marble figures, or black print on white paper, 
pictures in black and white. Colored pictures in which the bright 
colors of the spectrum like red, yellow and green, arc predominant, 
give good images. Metallic objects with polished surfaces give 
good images. Among these the works of a watch or small clock 
show well; also coins and medals. Bright metallic objects show 
best on a dark ground. 
Objects and pictures which are very light-absorbing naturally 
will not give good screen images, no matter how brilliant the light 
or good the apparatus. If the outlines of such objects are what is


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