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64
Fig. 5. Schematic diagram showing the path of rays through both openings at 64 mm, through prisms to the Yvar lenses, then on to 16mm film.
a window through which the spectator sees everything that has been photographed between 3.2 m and infinity.
Objects closer to the camera than this may be photographed. If the most distant plane of the subject is 3.2 m from the camera (Z>2 = 3.2), objects as close as 1.6 m (Z>i = 1.6) may be filmed. The image will then seem to be between the window and the spectator, and precautions should be taken while photographing so that features situated in front of the window will not seem to be cut off by its edges.
In order to photograph at distances of less than 1.6 m, it would be necessary to change the position of the frame in order for the entire view to lie within the stereoscopic depth of field.
The Kern-Paillard Instrument
The photographic instrument has been built as an accessory for the HI 6 De Luxe Paillard Camera. It is a compact assembly screwed to the turret in place of an ordinary lens ; it is automatically centered with respect to the axis of
Fig. 6. Left and right-eye Stereo images on standard 16mm movie film.
rotation of the turret, to prevent differences in height between the left-hand and right-hand images. The instrument comprises two Yvar lenses,/ = 12.5mm, aperture 1/2.8, with parallel optical axes 5.3mm apart. The normal base of 64 mm is obtained by a system of prisms placed in front of the lenses (see Fig. 5).
The two homologous images are located side by side on the 1 6mm film, and together occupy one 16mm frame (see Fig. 6).
The lenses are universally focused and adjusted to their hyperfocal distance. If we assume a circle of diffusion of 1/50 mm on the film, the depth of field of definition is 5 = 2.8/50 = 0.056mm on the print. The hyperfocal distance is therefore
X = f2/S = 156.25/0.056 = 2790mm,
or 2.8 m. The lenses being adjusted for 2.8 m, good definition can be obtained from 1.4 m to infinity at full aperture. Now we have seen that the stereoscopic depth of field permits us to photograph from 1.6 m to infinity. The universalfocus lens adjusted to hyperfocal distance is thus adequate for all cases.
The projection instrument takes the place of the lens of a standard 16mm projector. It comprises 2 Petzval lenses, / = 20 mm, aperture 1/1.6, whose optical axes are parallel and 5.6 mm apart (Fig. 7) ; the projection windows are centered with respect to these axes. In front of each of these two lenses, there is a polarizer; the planes of polarization of
522
December 1952 Journal of the SMPTE VoL 59