* PHOTOMICROSCOPE : J. H. G. MONYPENNY 149 



ideas, but so far as the author is aware, such an arrangement has 

 not been described before, nor has he heard of any similar apparatus. 



For such work the ordinary low power objective is not suitable — 

 its " field " is not big enough. The lens the author uses is the 

 35 mm. projection lens made by Zeiss, though probably equally 

 good results could be obtained with some of the very short focus 

 photographic lenses made by various opticians. As illuminator he 

 uses a piece of niicroscopic cover glass 1^ in. x IJ in., mounted 

 in a light brass frame which fits on to the objective. The frame 

 is pivoted, allowing the illumination to be adjusted to a nicety. 

 This disc is used between the objective and the section. 



If one is using an enlarging lantern or a projection lantern, then, 

 in order to get satisfactory lighting, as is well known, the condenser 

 must be close to the negative or slide and must focus the illuminant 

 on the projection lens. The same principle is used for photographing 

 metal sections, and the arrangement of condensers is shown diagram- 

 matically in Fig. 8, which shows the 35 mm. lens A attached to 



«rtle- t'ov^ 



Fig. 8. 



Condenser system for low power photography 



the microscope tube and the section B on the stage (the microscope 

 used is the large " Works " model made by Watsons, London, 

 which has a very wide tube — the inner draw tubes are removed for 

 use wdth this lens). The condenser D forms a considerably enlarged 

 image of the illuminant C (the 500 C.P. Pointolite Lamp) at E 

 close up to the second condenser F, and the latter in turn focusses 

 the image (after reflection at the 45° cover glass reflector G and 

 the surface of the specimen) on the lens A, as indicated roughly 

 by the dotted lines. The condensers used are 2J in. diameter, and 

 it is possible to illuminate evenly a section about 1 in. diameter; 

 this is more than required, as the field of the lens is only about 

 f in. diameter. Fig. 9 shows the apparatus set up, and Figs. 10 

 and II some of the results obtained. 



It is obvious that these low powers are of special value where 

 either the structure is very coarse, or where one wishes to show 

 the variation of structure over a fairly large area. For example, 

 Fig. 10 (x 15 diameters) shows far better than a photograph at, say, 

 100 diameters, the structure of the sample of overheated steel 

 from which it was taken. Fig. 11 ( x 15 diameters) illustrates another 

 type of photograph for which the ordinary microscopic objective 

 would be quite useless; this shows the size and distribution of 

 carbon in an unsound segregated area. This actual example is 

 rather unique, showing, as it does, high and low carbon areas in 

 close proximity. 



