Topics in..
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Edited by S. Z. LEWIN, N e w York University, N e w York 3, N. Y.
1. Measuring Microscopes
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art&, mt of whicn are to be c m t r i u by gust ahur8, are intended lo serve the reader8 of Ulis JOURNAL bfl d i n g a i h t h to neu, developmenls in the theory, design, w wilnbi1itu of chemical Iubo7ah-g imtmmalation, or by presenting useful insigh& and ezplanatwns of lo* fJ& are of practical importance to those who use, m teach the use of, mod.ern instmmkztion and instmmlal techniques.
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Shop Microscopes
A variety of so-called "shop microscopes" is available for the examination of machined parts, tool edges, cracks, scratches, bore holes, fine details of design and engraving, etc. An example of the simplest of these is the Model 233 Pocket Microscopeof PacificTransducer Corporation, Los Angeles, California 90064 ($20), shown in diagram in Figure 54. I t con-
XXIV. Instrumentation for Micrometry and Microscopy-Part
Four
5. Z. Lewin, Department o f Chemistry, N e w York University, New York, N . Y. 10003 Types of Compound Microscopes The objective and ocular lenses are the sine p a non of a compound microscope, but ot,her components must be provided if a practical and useful instrument is to he construet,ed. There is a variet,y of ways in whieh the abject under eaamirmtion may be illuminated, and in whieh the optics may he positioned relative t o it, as well as a number of means of modulating the light rays before and after passing through t h e magnifying lenses. Certain arrangements aud accessories have proved to be particularly useful for specific types of work; these correspond to instrumental designs which are eammonly designated b y the following specid names: 1. Measuring, Universal and Toolmakers' Microscopes; Comparators, Cathetometers. The basic microscope optics are combined with special devices for precise positioning and movement of the specimen or of seale~,crosshairs, reticles, or graticles for the estimation of distances or angles. Projection optics may be employed to permit t,he measurement of dimensions and profiles, and interference phenomena may be exploited far the quantitative estimation of roughness, elevation, and contour. 2. Standard Microscopes. The stage and illumination system are designed primarily for the observation of transparent specimens mounted on standard microscope slides. 3. Phase Afieroscopes. The contrast and resolution with whieh transparent specimens are seen in the standard microscope are greatly improved by the incorporation of accessories that make visihle the phase shifts which occur when light passes t,llrough media of differingrefractive indices.
4 . Stereo and Operations Microscopes. The optics are designed for s relatively large objective-to-specimen working distance, and for maximum flexibility in the positioning of the microscope wibh ~.espeet to the specimen. Stereoscopic viewing and inversion of the image are employed to facilitate manipulations performed on the specimen while it is under observation. 5. Chemical and Petrographic Microscopes. Accessories are incorporated that, polarize the light before it passes through the specimen, and then make visible the effect of the specimen on t,he constituent wavelength? of the polarized beam. The specimen holder (microscope stage) may be specially designed bo permit heating or cooling of the sample while it is under observation. 6. Biological Microscopes. The standard microscope is inverted, so that the underside of a flat, transparent specimen (e.g., a Petrie dish or culture flask) can be placed above the objertive, and the contents of the container viewed from below. 7. Melallographic Yicmscopes. The illumination system and optics are modified to optimize the image quality when viewing the surface of an opaque specimen by reflected light. 8. Photomicrographic Inslruments. The optics and illumination are modified to permit substitution of a camera for the observer's eye, and thus to permit the photographic recording of the image, whether for still, time-lapse, or cinemalogmphir presentation. 9. P~ojerlion Microscopes. The microscope image is projected onto n rrreen for simultaneous viewing by a group 01 persons.
Figure 54. Pocket Microscope, Model 233, of Pacific Transducer Corp. MognificoBan is varied by odiurting the distance between the objective and the eyepiece.
sists simply of an objective that is positioned a specific distance from the surface under examination by means of a surrounding mounting tube (the "chassis" in Fig. 54). The depth of focus of this objective lens is suficiently broad that the front focal plane of the ocular (eyepiere) can be varied over a range of about 2 in. without excessive loss of clarity in the final imaee. When the eveuiece is at the " lower limit of its range, the image it magnifies is smallest, and the over-all magnification seen by the observer is 20X. When the eyepiece is extended to its upper limit, the objertive image a l its front focal plane is ahout 3 X larger than in the previous rase, and the ove1.-all visual magnification is 60X.
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4 . somewhat more elaborate vorsion of this type of design is t h e P T C Model 232B Industrial Microscope ($43), t h e optical diagram of which is given in Figure 55. Two magnifications are provided; 2OX when the eyepiece is a t its closest positiuu to the objective, and 40X when i t is a t its far position. A spacer is pro-
Figure 55.
PTC lndurtriol Microscope, Model 232.
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vidrd t,o insure accurate uositionine of the eyepiece in these two lorations, and a rackand-pinion gear syalom allows adjustment, ~
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of the opbicsl train in its chassis in order to focus on bhe specimen surface. This device is also available without the rackand-pinion system (Model 232, $33). A shop microscope of sirnilas design to the above is t h e Swiss-made O X 4 G microscope, distributed in the U S . by Paul N. Gardner Co., FVashington 11,
D. C . (S30: maenificstion 10X-25X. 1 8 X 3 5 X , or 26X-SOX, depending upon (Conlimed on page 21856)
t,he eyepiece; additional eyepieces permitting changeover from one oi these ranges t o mother are $10.) Better image quality ran be achieved ii the obje
