not lying in the angle, given in fig. IV c, but in the angle as is to be seen in fig.
IV b. Again we see a double image. When shutting the right eye, the right part of
that double image will disappear; when shutting the left eye, the left part will
disappear.
So, without solving the problem how we get a double image, we are sure that
when looking at an object that is not lying near the intersection of the eye-axes, we
always observe a double image of that object, whether we stare or squint.
It is that ability of producing a double image that gives us the possibility of
getting a stereoscopic image.
The only thing we have to do is to choose a stereo-couple and to
make from one of these a double image by staring or squinting. We only need to
bring the other stereo-photo to the same place, where we see one of the parts of
the double image of the first photograph and then we get a stereo-image.
What is the solution of that problem?
Well, normally each of our eyes receives a flat reversed image of a given
object (fig. V).
The image on both retinas will be the same if the object is a flat one. But as
soon as we take an object with three dimensions, both images on the retinas will
be slightly different. We say that those images show different parallaxes. Accord-
ing to mathematical and physical laws we can know how great these parallaxes
will be.
With the help of our brain we make a reconstruction of these two images
and the result is that we “see” a three-dimensional object again.
How these things can happen is beyond our knowledge. The only
fact we really know is that the whole ability of men to “see” and “to see three-
dimensionally”, is the possibility that out brain makes that reconstruction in
any way. |
But at the very moment that we make a double image appear from one
photograph and we bring an additional stereoscopic photograph in the same place
of one of these double images, it is for us just the same as if an object itself were
to bring images on our retinas and that our brain made the combination.
Here we make that combination “free-handed”.
Of course there is a law that we should not neglect, for we know already
that staring or squinting has a different result. We know that when staring we
see the image that we think is made by our right eye, appear as the left one and
when squinting we see it as the right one. So we can understand that in both cases
the effect will be different, and so it is. But in both cases, staring or squinting, it
is the person himself who has to do the work to make the images double in one
way or another.
There is still another solution of the same problem and that is that another
person brings both images one upon the other.
It is the printer of the stereo-photographs who can do this work (fig. VI).
He can do this by applying vectographs, that is printing each of them in
such a way that, when using eye glasses of polaroid material, the right eye only
sees one of both photographs printed together, while the left eye only sees the
other one.
He can also establish the same effect by printing one of the photographs in
blue and the other in red. When using a red and blue filter we see only the blue
6
=.) Cc mr 09 + cto CS A
m t) Uo NN
