262 ORDINARY MICROSCOPE FOR PROJECTION [Cn. IX 



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 axis. 

 The mirror and the substagc 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, b\ 



For lod amplifier multiply the magnification 



For x2 projection ocular multiply the magnification 



For x4 projection ocular multiply the magnification 



For x2 compensation ocular multiply the magnification 



For x4 compensation ocular multiply the magnification 



For X4 Huygenian ocular multiply the magnification 



As the field of the projection apparatus is cut down by the vise 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 (254mm., 10 in.) and the relation does not hold strictly for the 

 much greater screen distances ( 357a). 



