The
points, A' and B', will be illuminated precisely at the same moment. As
the shutter continues its travel, a fresh quantity of rays coming from A
and B will be admitted, and the image will be illuminated more and more
up to the moment at which all the rays can pass. It will then possess
its maximum intensity. Then a portion of the rays from A and B being
intercepted, the image will become darker and darker until complete
extinction. The image here, then, is not produced successively as in the
former case, but is entire from the beginning. In this case the image of
our mast cannot be misshapen, since it has been accurately photographed
at the same moment.
The true place for the guillotine shutter, then, from a theoretical
standpoint, is in the interior of the objective. Are there any other
advantages to be gained by so placing it? Yes; it is easy to understand
that for the same time of exposure, and consequently for the same
result, the aperture may be so much the smaller in proportion as the
optical center is approached.
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