INDUSTRIAL RESEARCH 



generally required that the morphology of a the best possible instrumental performance 



living specimen be preserved, it is permissible cannot be realized unless certain precautions 



to be less inhibited as to embedding tech- are taken regarding adjustment, alignment 



niques, in particular, the solvents, tempera- of components, and the choice of optics and 



tures, and embedding media employed. illumination. 



Metal-shadow casting (7) is a techniciue by Fundamentally, a microscope consists of 



which a thin film of metal is vacuum evap- an objective, eyepiece, and condenser, and, 



orated onto the surface of a sample or a as such, is called a compound microscope, 



replica of that surface. This method creates a These components are held and manipulated 



subject on which differences in surface on a stand which is usually equipped with a 



morphology are evident due to an increase stage to hold the specimen. The condenser 



in reflectivity or absorption of the surface directs light to the specimen, the objective 



and/or a shadow effect. Metallization of receives the light changed by the specimen 



specimen surfaces by vacuum evaporation and produces the initial magnification of the 



has been used extensively in electron mi- image. The eyepiece, through which the 



croscopy; however, there are many applica- specimen is viewed, magnifies the image 



tions of the technique in light microscopy, created by the objective. The total magnifi- 



particularly in conjunction with surface cation of the viewed image is a product of 



replicas. Details of replication, metallizing, the magnifications of the objective and eye- 



and shadowing by vacuum evaporation are piece. There are many variations in types of 



given in the section on specimen preparation, objectives, condensers, and eyepieces. For 



This discussion of resolving limits, useful example, in vertical illumination a single 



magnification, and contrast is by no means lens may serve at the same tune the purposes 



complete; nevertheless, it is believed that the of condenser and objective. Again, since 



factors most significant to industrial mi- many types of illumination are required, 



croscopy were mentioned. Further detailed condensers are individually designed to 



information may be fomid in the references achieve specific results, 



cited or in other sections of this publication. Objectives are the most expensive com- 

 ponents of a microscope and from this 



Alignment, and Related Methods of standpoint, as well as from that of their role 



Illuniination j^^ image formation, deserve the concentrated 



Microscopes and methods of illumination attention of the microscopist as to then- selec- 



(1, 2) used with them cannot very well be tion. Objectives are classified with respect to 



divorced in any discussion of the principles optical correction. Some are chi-omatically 



involved. Consequently, they will be treated corrected to bring two wavelengths of light 



together; however, emphasis will be placed into focus at the same plane, and also cor- 



first on microscope function and construe- rected spherically for one wavelength. Ob- 



tion. Later, attention will be shifted to jectives having this degree of correction are 



methods of illumination, and finally the called achromatic objectives and are only 



selection of microscopes for nonbiological about one-third as expensive as apochi-o- 



application will be considered. matic objectives which are chi-omatically 



Although there are many types of micro- corrected for three wavelengths and spher- 



scopes, they are closely related in function, ically for two. Unless the microscopist is well 



and possess comparable components. There- grounded in the use of the microscope, 



fore, an understanding of the basic construe- images inferior to those obtained from 



tion and operation of one microscope may be achromats are likely to be realized from apo- 



applied in some degree to others. However, chromats. Achromats have smaller numerical 



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