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MICRO-PHOTOGRAPHY AND PROJECTION APPARATUS 329
The microscopic attachments used were achromatic objective number 4, and eye-piece I. An arc lamp was used for source of light, and the illuminating apparatus was shut to 7 mm. The camera extension was 32 cm. ; silver eosine plates were used, and the exposure allowed was 3 minutes.
It is sometimes necessary to photograph relatively large opaque objects, and the next figure shows how this can be done. The result of such an experiment is seen in fig. 139, which represents the photograph of an armadillo embryo in spirit. It has been magnified 1J diameters. The lens used was a microsummar of 80 mm. focal length, and the exposure lasted five minutes with a silver eosine plate.
A section of a microsummar is shown in fig. 140. These objectives have an aperture of //4.5, and are specially corrected for chromatic, spherical, and astigmatic dispersion.
By means of such an arrangement it is well to remember that it is possible to obtain many degrees of magnification with the same objective ; the shorter the camera extension the smaller will be the image.
Should stereoscopic photographs of any particular preparation be desired, all that is necessary is to move the object aside so that the second image on the screen may be displaced by an amount equal to the distance between the pupils of the eyes, that is, about 6*5 cm., and the apparatus allows of such displacement being made.
Of course any good brand of photographic plate will do for this work, but with stained preparations it is essential that some variety of orthochromatic dry plate should be used. No special remarks are necessary as to the management of the plates after exposure, but it