Reflecting Condensers.

Our improved Concentric Reflecting Condensers, as computed by Dr. F. Jentzsch,*) of our Research Dept., serve for observation in darkground illumination and are more especially adapted for bringing into view living and unstained bacteria.

Trace of rays through condenser and 1/i2/;

lens fitted with a conical stop No.

oil-immersion

113.

The essence of this mode of observation lies in the establishment of striking contrasts between the intensely bright bacteria and the dark back ground against which they are viewed. The condenser devised for this purpose has two reflecting surfaces, one convex, the other concave, as shown in the diagram, which are so arranged as to bring the rays to a point in a very perfect manner, with the result that an intense illumination of the bacteria is obtained. Since the optical arrangement consists of reflecting surfaces only it follows that no chromatic defects can arise, whilst the amount of spherical aberration which is left uncorrected does not exceed 0,7 per mille, which is practically negligible. It will thus be seen that the Concentric Reflecting Condenser approaches very closely the ideal condition of aplanatism.

That the actual trace of the rays conforms to what it should be theoretically will be seen from the annexed photo-micrograph.

*) Physikalische Zeitschrift, Vol. XI, pp. 993—1000, 1910, and Verhand-lungen der Deutschen Physikalischen Gesellschaft, Vol. XII pp. 975—991.

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