I'licro : ll; 



the specimen is formed at the point of focus of a ref;ular refracting 

 microscope objective. This image is then magnified by the objective and 

 further magnified by a regular ocular or eyepiece. In the other type of 

 reflecting objective (Figure Ub ), the mirror system alone forms a magni- 

 fied image of the specimen; this image is then further magnified by the 

 ocular. The performance of the second type of objective is superior to 

 the first, no doubt due in part to the fewer optical elements. 



The regular U3X achromatic objective of the American Optical Company has 

 a working distance of 0.73 millimeter, that of the Bausch & Lomb Company 

 is 0.6 millimeter; apochromatic objectives of comparable magnification 

 have much less clearance, being on the order of 0.18 millimeter, N'^wton & 

 Company, Ltd. makes a U millimeter reflection objectivt of one first type 

 described above, that is, a reflector plus refractor combination. This 

 device has a working distance of 12.8 millimeters. The well-known 

 British microscope maker. Beck Company, makes reflecting objectives of 

 the second type, which have .nagnifications and working distances as 

 followss 15X, 2U.0 mm.; 36X, 8.U mm.; 52X, 3.5 mm.; 7UX, 2.5 mm.; and 

 a water immersion objective of 172X (2^0 mm. body tube length only). 



Reflection objectives can be used on regular microscopes, provided there 

 is airple clearance on the nosepiece for the large diameter body of the 

 reflector objectives and provided the body tube can be elevated enough 

 to allow the objective to focus on a subject which may be in an observa- 

 tion chamber having appreciable thickness of its own. These objectives 

 have the standard Royal I-Iicroscopical Society thread so they can be 

 interchanged with the regular refracting objectives, if the other con- 

 ditions for installation permit. 



Reflection objectives have other advantages, besides possessing a rela- 

 tively long working distance, that ought to be mentioned for their value 

 in other applications. Unlike refracting objectives, the reflector units 

 are achromatic throughout the entire spectrum from long wave infra-red, 

 through the visible spectrum, to ultraviolet. Hence, observations and 

 absorptive spectra studies of living cell contents are possible. These 

 objectives are best for microspectroscopy work. There is also less glare 

 because of the reduced number of optical svirfaces. Most phytonematolo- 

 gists will, I think, appreciate these objective lenses for the usefulness 

 in viewing nematode activities in micro-obeervation chambers. 



