galton.org 237
Composite Portraiture
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My reflector in my present instrument is, I am a little ashamed to confess, nothing
better than a piece of looking-glass fixed to an axle within the camera, near its top left-
hand edge. One end of the axle protrudes, and has a short arm; when I push the arm back,
the mirror is raised; when I push it forward it drops down. I used a swing-glass because the
swing action is very true, and as my apparatus was merely a provisional working model
made of soft wood, I did not like to use sliding arrangements which might not have acted
truly, or I should certainly have employed a slide with a rectangular glass prism, on
account of the perfect reflection it affords. And let me say, that a prism of 2 inches square
in the side is quite large enough for adjustment purposes, for it is only the face of the
portrait that is wanted to be seen. I chose my looking-glass carefully, and selected a piece,
that was plane and parallel. It has not too high a polish, and therefore does not give
troublesome double reflections. In fact, it answers very respectably, especially when we
consider that perfection of definition is thrown away on composites. I thought of a mirror
silvered on the front of the glass, but this would soon tarnish in the gaslight, so I did not
try it. For safety against the admission of light unintentionally, I have a cap to the
focusing-screen in the roof, and a slide in the fixed body of the instrument immediately
behind the reflector and before the dark slide. Neither of these would be wanted if the
reflector was replaced by a prism, set into one end of a sliding block that had a large
horizontal hole at the other end, and a sufficient length of solid wood between the two to
block out the passage of light both upwards and downwards whenever the block is passing
through the half-way position.
As regards the fiducial lines, they might be drawn on the glass screen; but black lines
are not, I find, the best. It is far easier to work with illuminated lines; and it is important to
be able to control their brightness. I produce these lines by means of a vertical
transparency, set in an adjustable frame, connected with A, and having a gas-light behind
it. Below the eye-hole e, through which I view the glass-screen g, is a thin piece of glass
set at an angle of 450, which reflects the fiducial lines and gives them the appearance of
lying on the screen, the frame being so adjusted that the distance from the thin piece of
glass to the transparency and to the glass-screen g is the same. I thus obtain beautiful
fiducial lines, which I can vary from extreme faintness to extreme brilliancy, by turning
the gas lower or higher, according to the brightness of the image of the portrait, which
itself depends on the density of the transparency that I am engaged upon. This
arrangement seems as good as can be. It affords a gauge of the density of the negative, and
