In photographing with the microscope, it frequently occurs that the
operator, instead of devoting a negative to each of two or more similar
objects for comparison, printing both upon the same print, prefers to
have the whole series upon one negative, and taking from this a single
print. There is often room for two or more images upon the same plate. If
the center of the plate is devoted to one, obviously no more can be
accommodated on it, but by placing one at each end, or one on each
quarter of the plate, both economy of plates and convenience of printing
are secured. The end may be readily accomplished by matting the plate as
a negative is matted in printing.
Suppose it be desired to photograph four different species of acari on
one plate, the image of each when magnified to the desired extent only
covering about one-fourth the exposed area of the plate. First, a mat is
prepared of card-board or thick non-actinic paper, which is adjusted to
exactly fill the opening of the plate holder, lying in front of and close
against the plate when exposed, and having one-quarter very exactly cut
out. A convenient way to fit this mat is to leave projecting lugs on each
side at exactly the same distance from the ends, and cut notches in the
plate-holder into which the lugs may closely fit. If this work is
carefully done, the mat may be reversed both sidewise and endwise, and
the lugs will fit the notches; if so, it is ready for use. The object
being focused upon the focusing glass or card, the camera is raised
one-half the vertical dimension of the plate and displaced to one side
half the horizontal dimension, when the image will be found to occupy
one-quarter of the plate. The mat being placed in the plate holder, a
focusing glass is inserted in the position the plate will occupy, and
final adjustment and focusing made. The plate is then marked on one
corner on the film side with a lead pencil, placed in the holder without
disturbing the mat, and the exposure made. When the plate is replaced for
a second exposure, either the mat is reversed or the plate turned end for
end; but it is best to always place the plate in the holder in the same
position and change the mat to expose successive quarters, but this
requires the camera to be moved for each exposure.
With similar objects, and some judgment in making two exposures,
negatives may be made with almost exactly the same density in each
quarter, and by cutting out slightly less than one-quarter of the mat the
four images will be separated by black lines in the print; by cutting out
a trifle more than the exact quarter, they will be separated by white
lines instead of black.
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