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CH. IX]
HIGH POWER MICRO-PROJECTION
281
§ 406. Range of objectives to use with a substage condenser. —
Objectives of 16, 12, 10, 8, 6, 4, 3, and 2 mm. equivalent focus are used with the substage condenser. For objectives of longer focus than 16 the substage condenser of the ordinary form is rarely used. Either a special long focus substage condenser is used or the ordinary one is turned aside and the cone of light from the large condenser used as directed above (§ 376).
§ 407. Change in position of the substage condenser for different objectives and thickness of slides. — For the highest powers
FIG. 156. PROJECTION MICROSCOPE OF ZEISS.
(From the 4th edition (1899) of Zeiss1 catalogue of instruments and appliances for PhotoMicrography and Projection).
This projection apparatus, which in its main features was described in Zeiss microscope catalogue No. 28, (1889), and No. 29 (1891), consists of an optical bench on which all of the parts needed move separately so that any desired arrangement can be made for projection of large objects with low power or smaller objects with high powers.
Commencing at the right:
1 Arc lamp with inclined carbons, and with fine adjustments to center the source of light (crater of the positive carbon).
2 First element of the condenser consisting of a meniscus and a planoconvex lens, to render the light beam parallel.
3 Water-cell.
4 Second element of the condenser to converge the light-beam.
5 Iris diaphragm to cut down the light-cone if desirable.
6 Stage and substage condenser.
7 Projection objective and fine focusing device. In the figure no ocular is used.
This arrangement of the parts enables the user to employ a microscope with oculars or amplifiers, or the simple apparatus here shown, or photographic objectives.