Clapham.
_Stereoscopic Pictures with One Camera_ (Vol. vi., p. 587.).--In reply to
the inquiry of RAMUS, allow me to say the matter is not difficult. My plan
is as follows:--Suppose a piece of still-life to be the subject. Set up the
camera at such a distance as will give a picture of the size intended,
suppose it sixteen feet from the principal and central object; by means of
a measuring tape or a piece of string, measure the exact distance from the
principal object to the front of the camera. Take and complete the first
picture; if it prove successful, remove the camera about two feet either to
the right or left of its first station (_i.e._ according to the judgment
formed as to which will afford the most artistic view of the subject),
taking care by help of the tape or string to preserve the same distance
between the principal object and the camera, and that the adjustment of
focus is not disturbed. In other words, the camera must be moved to another
part of the arc of a circle, of which the principal object is the centre,
and the measured distance the radius. If the arc through which the camera
is moved to its second station be too large, the stereoscopic picture will
be unnaturally and unpleasingly distorted. The second picture is now to be
taken.
If the subject be a sitter, it is of the utmost importance to proceed as
quickly as possible, as the identical position must be retained movelessly
till both pictures are completed. This (in my experience) is scarcely
practicable with collodion pictures, unless by the aid of an assistant and
two levelled developing-stands in the dark closet; for the time occupied by
starting the first picture on its development, and preparing the second
glass plate (scarcely less than three or four minutes), will be a heavy tax
on the quiescent powers of the sitter. This difficulty is avoided by
adopting the Daguerreotype process, as the plates can be prepared
beforehand, and need not be developed before both pictures are taken. In
this case the only delay between the pictures is in the shifting the
position of the camera. This is readily done by providing a table of
suitable height (instead of the ordinary tripod), on which an arc of a
circle is painted, having for its centre the place of the sitter. If the
sitter be at the distance of eleven or twelve feet (my usual distance with
a 3¼ inch Voightlander), the camera need not be moved more than ten or
twelve inches; and even this distance produces some visible distortion to
an accurate observer.
The second levelling stand is required when using the collodion process,
because the second {71} picture will be ready for development before the
developing and fixing of the first has set its stand at liberty.