Stereoscopic microscopy (See also p. 532) 



BASIC DESIGN, OPERATION AND USE 



The stereomicroscope differs from the 

 conventional compound laboratory micro- 

 scope in several respects: 



(1) it is actually two compound micro- 

 scopes aimed at a common object; 



(2) the image is erect and non-reversed; 



(3) the image is truly stereoscopic, or 

 three-dimensional, as contrasted with the 

 binocular body of a conventional microscope 

 which presents identical images to both eyes, 

 and hence is not stereoscopic; 



(4) the useful magnification limit is much 

 lower, generally 100 to 150 X, as contrasted 

 with 1000 to 1500 X in a normal compound 

 microscope. 



From the foregoing, it is apparent that 

 the stereomicroscope gives an image which 



PAIRED 

 EYEPIECES 



PORRO ERECTING 

 PRISM SYSTEMS 



SPECIMEN 



Fig. 1. The basic optical elements of a stereo- 

 microscope in its simplest form. The Porro prisms 

 serve not only to erect the image, but provide a 

 simple means for changing the interocular dis- 

 tance to suit the observer. 



is much more easily interpreted than those 

 obtained with the laboratory microscope. 

 The low magnification is a factor in this 

 easy interpretation, since one sees a good 

 deal of the actual object, and can easily 

 gain the impression of simply being brought 

 closer to a familiar object. 



True stereoscopy is also a potent factor in 

 creating realism in the image. The observer 

 sees the depths and heights standing out 

 clearly and quite naturally, and the transi- 

 tion from normal viewing to microscope 

 viewing is easily made. The stereomicroscope 

 has quite a large depth of focus, so that the 

 sense of depth perception is heightened 



accordingly. 



The erect and non-reversed image also 

 creates a natural and easily understood 

 knage. It also permits one to easily manipu- 

 late the specimen on the stage, without the 

 attendant frustration involved in attempts 

 to do the same thing on the laboratory 

 microscope. This permits use of the stereo- 

 microscope in many appUcations where very 

 precise manipulations must be made, such 

 as micro-dissection of biological material, or 

 assembly of tiny electronic components in 

 the industrial field. 

 Structure of the Stereomicroscope 



Figure 1 shows the basic structure of a 

 simple stereomicroscope. The left and the 

 right microscopes aim toward a common 

 object field. Each microscope comprises an 

 objective, a prism-erecting system, and an 

 eyepiece. Each prism system is mounted on 

 a bearing concentric with the objective axis, 

 around which it may be rotated to adjust it 

 to the observer's interocular distance. 



Normally the angle between the two mi- 

 croscope axes is in the neighborhood of 10°, 

 which is about the normal convergence 

 angle for viewing an object at 15 inches 

 distance. 



538 



