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THE
CAMERA LUCIDA
“The farther the prism is
removed from the paper, that is, the longer the stem is drawn
out, the larger the objects will be represented in the drawing
and accordingly, the less extensive the view.
The nearer the prism is to the paper, the smaller will be
the objects, and the more extensive the view comprised on the
same piece of paper.
In copying drawings, the
copy will be larger or smaller than the original, according as
the prism is more or less distant from the paper than it is from
the drawing to be copied.
Thus, if the drawing be two feet from the prism, and the
paper only one foot, the copy will be half the size of the
original. If the
drawing be at one foot, and the paper three feet distant, the
copy will be three times as large as the original; and so for
all other distances.”
DIRECTIONS FOR USING THE CAMERA LUCIDA
“The Instrument being
fixed by the screw and clamp to the table and paper on which the
drawing is to be made, its stem should be inclined so as to
bring the prism nearly over the centre of the paper, and the
pin, on which the prism turns, placed truly horizontal.
The Instrument, as
represented in the figures, may be used either with the small
round glass, turned up in front, Fig 1, or with the larger
glass, turned up level underneath the Instrument, Figure 2,
(seen from above.)
But those who are short-sighted can only use the former, and
persons that are long-sighted must use the latter.
The prism is next to be
turned upon its pin, till the transparent rectangular face be
placed opposite to the objects to be delineated, when the upper
black surface of the eye-piece (Figure 2) will be on the top of
the Instrument; and through the aperture in this, the artist is
to look perpendicularly downwards at his paper.
The black eye-piece is
moveable, and in ordinary circumstances, is to be in such a
position, that the edge of the small transparent part at the
back of the prism shall intercept about half the eye-hole.
The artist then, looking through the eye-hole directly
downwards at his paper, should see the objects he wishes to
draw, apparently distributed over the paper.
For, since his eye is larger than the eye-hole, he sees
through both halves of the hole at the same time, without moving
his head. He sees
the paper through the nearer half, and sees the objects at the
same time through the farther half, apparently in the same
direction, by means of reflection through the prism.”
THE POSITION OF THE
EYE-HOLE
“The position of the
eye-hole is the circumstance, above all others, necessary to be
attended to in adjusting the Camera Lucida for use; for, on the
due position of this hole depends the possibility of seeing both
the pencil and the objects distinctly at the same time.
If the eye-hole be moved,
so that nearly the whole of its aperture be over the paper, and
a pencil and paper will be very faint.
But there will always be an intermediate position
(varying according as the objects or the paper happen to be most
illuminated) in which both will be sufficiently visible for the
purpose of delineation, though not quite so clear as to the
naked eye. This
intermediate position is easily found, with a little practice.
If objects can be seen
distinctly on the upper part of the paper, but not upon the
lower, the Instrument requires to be turned upon its pin, so
that the transparent face may be inclined rather downwards, and
the contrary for seeing the upper part of the view.
Many persons, upon first
attempting to use this Instrument, occasionally lose sight of
their object or their pencil, merely by means of a little motion
of their head, backwards and forwards, of which they are not
aware, in breathing; but a very little practice soon obviates
this difficulty.”
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