With low power objectives the light in the field in 

 the eyepiece is stronger than that from the paper. It 

 may be modified 



by using plane mirror, 



by covering the mirror with tissue paper, 



by using a small opening of the substage diaphragm. 



With the higher powers the conditions are reversed 

 and the field of the paper appears brighter than that 

 in the eyepiece. 



In this case reduce the light on the paper by using 

 a tissue paper or opaque screen. 



Use substage condenser and modify light with the 

 iris diaphragm. 



Arrangement of Drawing Surface. As has 

 been stated this should be at right angles to the axis 

 of the projected image. In all camera lucidas the 

 reflecting mirror is quite close to the tube of the 

 microscope which is supposed to be in upright position 

 and if set so that the axis of the cone of projected rays 

 is vertical, there will be no distortion, or in other words 

 the field of view will be perfectly circular. It will 

 be found, however, that the stage and base of the 

 microscope will project within this circle and so 

 prevent obtaining a complete drawing of the object. 

 The mirror of the camera lucida must therefore be so 

 tilted as to throw the cone of rays farther away from the 



171 



