260 



MAGNIFICATION IN MICRO-PROJECTION 



[CH. IX 



391a. In preparing this table the apparatus shown in fig. 121, 138 was 

 used. The second element of the condenser giving the cone of light, had a focus 

 of 30.3 cm. (8 in.), and the stage was moved up in the light cone (fig. 132) to 

 give the largest and brightest field possible for the given objective. No sub- 

 stage condenser was used except for the 2 mm. oil immersion. 



A stage micrometer in millimeters, tenths and one-hundredths was used as 

 object. The screen image of one or more of the micrometer divisions was 

 measured with a metric rule and the magnification obtained by dividing the 

 size of the image by the known size of the object. For example: if the 

 micrometeris in one-tenth millimeters (o.i mm.) and the screen image of two 

 spaces (0.2 mm.) measures 20 centimeters or 200 mm. the magnification of the 

 screen image must be 200 divided by 0.2 = 1000. That is, the image is one 

 thousand times the size of the object, therefore, the magnification of the pro- 

 jection apparatus in that case is 1000. The size of the field of the projection 

 apparatus is found by the use of the micrometer as follows: The micrometer 

 is arranged on the stage so that the image shows one of the lines on one edge 

 of the field (the circle of light). Then one simply counts the spaces to the 

 other edge of the field. For example, suppose that it requires 14 of the o.i 

 mm. spaces, then the size of the field is 1.4 mm. and an object larger than this 

 cannot be projected entire with this objective. 



To get the size of the screen image of this field a tape measure or meter stick 

 is used and the diameter of the circle of light on the screen is measured. 



This method of finding the size of the field of the projection apparatus, the 

 magnification and the size of the screen image, depends upon direct observation 

 anil is applicable to any projection outfit whether an objective only or an objec- 

 tive and an amplifier or an objective and an ocular are used (see also 392a). 

 The amplifiers used had a free opening of 36 mm. (i y^ in.), and were placed at 

 the end of the large tube (fig. 133) at a distance of about 1 1 cm. (4^4 in.) from 

 the objective. 



