A shot, if taken with an appropriate lens angle, camera distance and viewed with a specified screen size and viewing distance (see next chapter), will replicate the retinal image, but this image will not neces- sarily be the same as how an observer views the same field of view.
With the above conditions, the camera will provide true geometrical perspective, but because we do not see the world as it is projected on the retina, the perspective of the shot may look wrong. For example, a holidaymaker takes a photograph of an impressive range of moun- tains. Looking at the print, the holidaymaker may be disappointed because the mountains look very small compared with their memory of the landscape (see Figure 3.2).
The mismatch between how we think we see a subject and how the camera records the same subject is due to a perceptual distortion called size constancy. This is the tendency for the perceptual system to com- pensate for changes in the retinal image with viewing distance. As a retinal image, a person walking away from a static observer halves in size as their distance from the observer doubles. The relationship between image size and distance from the observer is a constant, but in normal perception it is not seen as a constant. Perception adjusts the perceived size to match our knowledge of the size of the receding subject. Light source Pupil Iris Cornea Optic nerve Lens Retina Extrinsic muscle Blind spot Fovea Ciliary muscle Retinal image input signal Visual memory input Visual part of
the brain – over 30 areas dealing separately with colour size depth movement shape attention faces etc.
Figure 3.1 The contemporary theory about the brain and perception is that the visual brain has two systems:
There is part of the brain that generates images from the eyes (front projection); there is also a part of the brain that uses visual memories (back projection) There is no adequate explanation of how these two parts of the brain are combined in perception. Perception is an active process by the brain that invents, ignores, distorts what is coming through the eyes
We habitually underestimate the change in size of a person walking towards or away from us and mentally picture them modified in size but only with a slight alteration to their ‘normal’ size. An audience will appear from the front to have similar size faces and yet, to an observer, the retinal image of the faces of the people in the back rows will probably be a tenth of the size of the faces of the people in the front row. We never recognize that the image of our face in the mirror is always much smaller than its actual size. These are all depth indicators we habitually ignore or make the necessary adjustment for, as in the phenomenon of the ‘upside down’ image that is focused on the retina of the eye. We ‘mentally’ correct this inversion of our field of view as we subconsciously ‘correct’ the change in size. Size constancy is what the brain does and the camera does not do and therefore when plan- ning a shot we should not be misled by this habitual distortion.
A simple experiment demonstrating this phenomena is described by R.L. Gregory in Eye and Brain (1967):
Look at your two hands, one placed at arm’s length the other at half the distance – they will look almost exactly the same size, and yet the image of the further hand will be only half the (linear) size of the nearer. If the nearer hand is brought to overlap the further, then they will look quite different in size.
To ‘see’ like a camera obviously requires overcoming this everyday mental adjustment in the perceptual process. Many artists have trained themselves to accurately draw their perceptual image whereas most of us are trapped, particularly when taking photographs, in the percep- tual misconception of size constancy. In essence we see what we think is there, not what is actually there.
This characteristic of perception in habitually making adjustments to the size of a subjects at various distances from the viewer provoked a heated debate in the mid-nineteenth century when artists began basing painting on photographs. Always assuming that a lens/camera distance provided ‘normal’ perspective in a photograph (see Chapter 4, ‘The lens and perspective’), there was fierce criticism on what many people thought was the gross distortion in the painting depiction of size relationships. People were for the first time confronted with their adjustment of optical size as presented on the retina and the optical truth of a photograph transcribed into a painting (e.g., the holiday- maker disappointed with his photograph of a diminutive mountain range).
In 1858, Mrs Jane Carlyle complained about a Robert Tait painting of herself and husband in their drawing room, claiming that it was bad enough to be recorded for posterity with a frightful table cover, but what was worse was that their dog Nero, in the lower right fore- ground, was as big as a sheep. What was called the ‘false and ugly perspective of a ‘‘photographic’’ painting’ was in fact the true optical perspective showing size relationships as they were, not how we ima- gined they were.
Manipulating size relationships and the perspective depth of the shot is one of the principal compositional devices in film and TV productions. Seeing as a camera does requires not only retraining our habitual way of discounting the actual size of objects in a field
The lens, the eye and perception 29
Figure 3.2 The mismatch between how we think we see a subject (a) and how the camera records the same subject (b) is due to a perceptual distortion called size constancy. This is the tendency for the perceptual system to
compensate for changes in the retinal image with viewing distance
of view, but also mentally conceiving the visual effect of choosing different lens angles and camera distances.