Of the eye
If the eye is
required to look at an object placed too near to it, it cannot judge of it well
– as happens to a man who tries to see the tip of his nose. Hence, as a general
rule, Nature teaches us that an object can never be seen perfectly unless the
space between it and the eye is equal, at least, to the length of the face.
When both eyes direct the pyramid of sight to an object,
that object becomes clearly seen and comprehended by the eyes.
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On painting
Objects in relief, when seen from a short distance with one
eye, look like a perfect picture. If you look with the eye a, b at the spot c, this point c will appear to be at d,
f, and if you look at it with the eye
g, h will appear to be at m.
A picture can never contain in itself both aspects.
Good ref for looking at things first with one eye then the other at
beginning of thesis.
Let the object in relief t
be seen by both eyes; if you look at the object with the right eye m, keeping the left eye n shut, the object will appear, or fill
up the space, at a; and if you shut
the right eye and open the left, the object (will occupy the) space b; and if you open both eyes, the object
will no longer appear at a or b, but at e, r, f. Why will not a
picture seen by both eyes produce the effect of relief, as [real] relief does
when seen with both eyes; and why should a picture seen with one eye give the
same effect of relief as real relief would under the same conditions of light
and shade?
Page 21
An experiment showing that though the pupil may not be moved
from its position the objects seen by it may appear to move from their places.
If you look at an object of some distance from you and which
is below the eye, and fix both your eyes upon it and with one hand firmly hold
the upper lid open while with the other you push up the under lid – still keeping
your eyes on the object gazed at – you will see that object double; one [image]
remaining steady, and the other moving in a contrary direction to the pressure
of your finger on the lower eyelid. How false the opinion is of those who say
that this happens because the pupil of the eye is displaced from its position.
Of the plane of glass
Perspective is nothing else than seeing a place [or objects]
behind a pane of glass, quite transparent, on the surface of which the objects
behind that glass are to be drawn. These can be traced in pyramids to the point
in the eye, and these pyramids are intersected on the glass plane.
Page 53
Good Ref to go by Durers
woodblock demo of using a pane of glass
Why when an object is placed close to the eye its edges are
indistinct
When an object opposite the eye is brought too close to it, its
edges must become too confused to be distinguished; as it happens
with objects too close to a light, which cast a large and indistinct shadow, so
is it with an eye which estimates objects opposite to it; in all cases of
linear perspective, the eye acts in the same way as the light. And the reason
is that the eye has one leading line (of vision) which dilates with distance
and embraces with true discernment large objects at a distance as well as small
ones that are close. But since the eye sends out a multitude of lines which
surround this chief central one and since these which are farthest from the
centre in this cone of lines are less able to discern with accuracy, it follows
that an object brought close to the eye is not at a due distance, but is too
near for the central line to be able to discern the outlines of the object. So
the edges fall within the lines of weaker discerning power, and these are to
the function of the eye like dogs in the chase which can put up the game but
cannot take it. Thus these cannot take the objects, but induce the central line
of sight to turn upon them when they have put them up. Hence the objects which
are seen with these lines of sight have confused outlines.
Page 57
Why an object is less distinct when
brought near to the eye, and why with spectacles, or without the naked eye sees
badly either close or far off [as the case may be].
Page 58
Natural perspective acts in a contrary way; for, at greater
distances the object seen appears smaller, and at a smaller distance the object
appears larger. But this said invention requires the spectator to stand with
his eye at a small hole and then, at that small hole, it will be very plain. But
since many (men’s) endeavour at the same time to see one and the same picture
produced by this artifice only one can see clearly the effect of this
perspective and all the others will see confusion. It is well therefore to avoid
such complex perspective and hold to simple perspective which does not regard
planes as foreshortened, but as much as possible in their proper form. This simple
perspective, in which the plane intersects the pyramids by which the images are
conveyed to the eye at an equal distance from the eye is our constant
experience, from the curved form of the pupil of the eye on which the pyramids
are intersected at an equal distance from the visual virtue.
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Whence it follows, that when the eye
is somewhat removed from the [station point of the] perspective that it has
been gazing at, all the objects represented look monstrous….
Page 65
The medium lying between the eye and the object seen, tinges
the object with its colour, as the blueness of the atmosphere makes the distant
mountains appear blue…
Page 160
It is impossible that painted
objects should appear in such relief as to resemble those reflected in the
mirror, although both are seen on a flat surface, unless they are seen with
only one eye; and the main reason is that two eyes see one object behind
another as a and b see m and n. m
cannot exactly occupy [the space of] n
because the base of the visual lines is so broad that the second body is seen
beyond the first. But if you close one eye, as at s the body of f will
conceal r, because the line of sight
proceeds from a single point and makes its base in the first body, whence the
second, of the same size, can never be seen.
Page 268
A picture of objects in perspective will look more lifelike
when seen from the point from which the objects were drawn.
If you want to represent an object near to you which is to
have the effect of nature, it is impossible that you r perspective should not
look wrong, with every false relation and disagreement of proportion that can
be imagined in a wretched work, unless the spectator, when he looks at it, has
his eye at the very distance and height of direction where the eye or the point
of sight was placed in doing this perspective. Hence it would be necessary to
make a window, or rather a hole, of the size of your face through which you can
look at the work; and if you do this, beyond all doubt your work, if it is
correct as to light and shade, will have the effect of nature…
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