Bauhaus-Universität Weimar

Optic Projection: Principles, Installation and Use of the Magic Lantern, Projection Microscope, Reflecting Lantern, Moving Picture Machine
Gage, Henry Simon and Henry Phelps Gage
Micro-Projection with an Ordinary Microscope 
§ 393. Magic lantern with optical bench and ordinary micro¬ 
scope.—If one has a magic lantern with an optical bench, the 
bellows and lantern-slide objective may be removed and an ordinary 
microscope put in place. The microscope is made horizontal and 
firmly clamped to a suitable block (fig. 145, 187). This block 
should be furnished with cleats or grooved so that it will slide on 
the rods or guides of the magic lantern, and be of sufficient height 
to put the objective and tube of the microscope in the optic ««- 
The mirror and the substage condenser may be removed or turned 
aside and the object lighted by the cone directly from the large 
condenser as in fig. 145 or the condenser and ocular may be left 
in place (fig. 187). 
field is magnified, hence to get the size of the screen image, the size of the field 
is multiplied by the magnification of the apparatus in any given case. In the 
case of the 20 mm. objective the entire field measures 8 mm., hence its screen 
image, with a magnification of 250, should be 8 x 250 = 2000 mm. or 2 M. 
If one compares the tables obtained by actual measurement and that 
obtained by calculation it will be seen that they do not exactly agree. This is 
due to two things: first, the rated focus of the objective is only an approxima¬ 
tion, and second, the measurement of the diameter of the screen image is not 
very exact from the difficulty of deciding just where to begin and where to 
leave off in measuring to get the magnification and for determining the size of 
the field or the screen image of the field. 
The table of calculated values is only for the objective without the use of 
amplifiers or oculars. 
If one knows the magnification of the objective for a given screen distance 
the magnification obtained when using an amplifier or an ocular with the 
objective may be obtained approximately as follows: 
For —5d amplifier multiply the magnification of the objective only, by 1.70 
For —jod amplifier multiply the 2.50 
For x2 projection ocular multiply the 2.00 
For x4 projection ocular multiply the 3.70 
For x2 compensation ocular multiply the 2.05 
For x4 compensation ocular multiply the 4.20 
For X4 Huygenian ocular multiply the 4.20 
As the field of the projection apparatus is cut down by the use of an amplifier 
or an ocular one must determine the size of the field by the use of a micrometer 
as with the objective alone. The screen image can then be calculated by 
multiplying the observed size of the field by the magnification of the combined 
objective and ocular or amplifier. It will be seen that the objective with an 
ocular x2 or X4 does not give a magnification exactly twice or four times as great 
as the objective alone. The oculars are rated for the ordinary distance of 
distinct vision (254 mm., 10 in.) and the relation does not hold strictly for the 
much greater screen distances (§ 357a).


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