somehow "perceives" the full conical visual field which is like a
flashlight spreading out from the aperture of the camera,
as shown in
the diagram on the right above in which the visual field is diverging
from the Focus1.
On the other hand, the photo on the left above looks
like it being recorded by a tunnel vision, i.e., the visual field is
the same for near and far objects. For a tunnel vision objects would
appear the size as their actual size no matter where they are; thus
objects would not change size at all.
The film has a limited space
(35mm for standard format); therefore, it is impossible for a film to
record the full conical visual field as the camera "sees".
As we know,
to produce a scene somewhat close to what we actually see in the real
world the photographer has to connect many photos together side by
side. So a photo can merely record a small part of the visual field.
The camera does not record the sizes of objects on the film according to the
limited visual field allowed by the film; it does so based on the full
conical visual field it "sees" in the real world and the portions of
objects in the visual field.
What we see in a photo is not the true
relationship between objects and visual field volume; what we see
is the result of this relationship in the real world. The illusory effect in the photo
above is due to the fact that what have been recorded on the film does not reflect the real visual
field volumes associated with the figures and the photo is two dimensional.
It is the same with the photos of the Ames Room.
Someone might point out that it
is ridiculous for a camera to "perceive" the visual field and make a
decision before the images reach the film.
One can use the old size
equation θ = S / D
to make the point, that is, for a certain size S
an object's size on our retina and also on the film (since the retina
and film are always considered equivalent by perception researchers) is
determined by the distance D
. As such, the size of objects on
the film is always smaller when they are farther away and always larger
when they are closer to the camera.
The film records this size
obediently without exception. The size of objects on the film has
nothing to do with the conical visual field volume outside the camera.
Well, let's look at the pictures below which we have seen in the previous article
. The top photo was taken by the camera with a focal
length of 18mm, covering more than 100° angle of view.
The middle photo was taken with
a focal length of 34mm, covering about
60° angle of view. And the bottom photo was taken with a focal
length of 55mm, covering about
40° angle of view.
The distance between the back blue bottle and
the film is the
same for all three photos. However, the size of the back blue bottle is
quite different on the film depending on the sub-visual field volume
regulated by the angle of view of the camera.
These pictures demonstrate that the objects' size can certainly
alter on the film when distance between them is unchanged. This deals
another blow to the old size
equation θ = S / D
By the way, the front pink bottle in the photos does not change
as much in size. We can consult the diagram above for the answer. When
the converging angle changes, the portion of near objects in the visual
field does not change as much as far objects' portion in the changing