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No. 29. *Centring Achromatic Condenser, numerical aperture 1.0, equi- 

 valent focal length 14 mm. Fig. 11 p. 32. 



In this form of condenser, stopping down the illuminating rays is effected by 

 means of an iris -diaphragm situated between the lenses, where- 

 fore the diaphragm of the illuminating apparatus should remain 

 fully open. 



No. 30. *Centring Achromatic Condenser possessing great dis- 

 tance between its focus and its front lens, numerical aperture and focal 

 length as above. This form of condenser was suggested by Professor ROLLETT 

 of Graz. It is specially designed to admit of the use of ZOTH'S cooling trough 

 which should be placed directly below the object (see p. 93). 



The aperture is regulated by means of the iris-diaphragm of the illumin- 

 ating apparatus. 



No. 31. *Centring Achromatic Condenser with enlarged aperture, 



numerical aperture 1.30, equivalent focal length 9 mm. By virtue of its large 

 numerical aperture this condenser admits of the application of an exceptionally 

 large or of a very oblique illuminating cone, unaffected with the pro- 

 nounced aberrations invariably present in the cone of rays yielded by ordinary non- 

 achromatic condensers. The slides used with this apparatus may not exceed a 

 thickness of about 0.7 mm. 



The aperture is here also regulated by means of the iris-diaphragm of the 

 illuminating apparatus. 



Regarding the advantages of the Achromatic Condenser over the ordinary, see our catalogue 

 relating to Micro-photographic Apparatus, 5 th Edition 1903, p. 31. 



The Centring Achromatic Condensers Nos. 2931 are inserted bodily into 

 the sliding sleeve of the illuminating apparatus from above, and in order 

 to permit this insertion, the microscope should be canted and the illuminating 

 apparatus racked well down. 



Centring Achromatic Condenser, num. Ap. 1.0, in case . 



Centring Achromatic Condenser, num. Ap. 1.0, with great 



distance between focus and front lens, by ROLLETT, 



in case 



Centring Achromatic Condenser, num. Ap. 1.30. in case 



Marks Codeword 

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100. Papula 

 100. Paqiiira 



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