Excerpt from The Photography of Aquatic Animals in Their Natural Environment

If the ground glass is put in place and brought by focusing into the plane I I', then the sharp image of distant clouds and trees is seen on it, while the image of the fish lies behind the ground glass and is no longer clearly visible. If the water is smooth, a plate exposed under these circumstances gives a sharp negative of these distant objects, but does not show the fish.

If one looks at the fish in the water from the point 0 it is seen clearly, because its image is focused on the retina, while the images of more distant objects mirrored in the water's surface fall in front of the retina, and the objects from which they come are therefore not seen. The observer neglects the glare of light from these distant objects, fixes his attention on the fish, and sees it. If now, while still looking toward the fish, he adjusts his eye to distant objects by relaxing the ciliary muscle, these are clearly seen mirrored in the surface of the water, while the fish is no longer sharply seen. Similarly, if a mirror is laid on the ground so as to reflect the clouds and its image is examined by focusing in a camera, it is impossible to get at the same time on the ground glass a sharp image of the clouds reflected in the mirror and of the frame of the mirror or other near object. It is only when the mirrored object lies near the surface of the water that its image can be focused on the photographic plate or retina at the same time with that of a submerged object near the surface. It nearly always happens that the light entering the camera from distant objects mirrored in the surface of the water is so much more intense than that from submerged objects that the images of the latter are quite obliterated on the photographic plate. Sometimes, on the other hand, when the camera is pointed nearly vertically into the water at an object over a light-colored bottom, the emerging light is more intense than the reflected light, and there is obtained a more or less fogged negative which shows submerged objects. This is the more apt to be the case if the photographer has the sun at his back. (see Saville - Kent, At other times, within the limits of the reflected image (not the shadow) of a dark-colored bridge or building or of dense foliage, one may obtain a fogged negative, showing submerged objects. In this case also the partial success is due to the fact that the reflected light is less intense than that which comes from the submerged objects to be photographed. It is not often, however, that the submerged objects that one wishes to photograph are found within the reflected images of dark-colored backgrounds of sufficient size and far enough away.

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