Then the point, A', gradually becomes
obscured and disappears; and the same is the case with all parts of
A'B'. The image is developed progressively from A' to B', and makes its
impression upon the sensitive plate successively--a fact which, as
may be conceived, may have its importance. If, for example, we are
photographing a ship that is being tossed about by the sea (and we
borrow this example from our colleague, Mr. Davanne), the image of the
top of the mast will not be formed at the same instant as that of the
base, and if the motion of the mast has sufficient extent it may take on
a curved form, due to the fact that it has effected a movement between
the moments during which its apex and base were being photographed.
Upon placing the guillotine shutter in the optical center of the
objective, what will occur? The shutter will permit the passage of an
equal fraction of the rays derived from A and B, that is to say, the
image will be complete from the first instant of the exposure.
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