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slide. The counter will start at number 10. Since
switches S8 and S9 are physically attached to
the counter, the camera will cycle through 10
exposures even though there be less than 10
sheets of lm in the pack. This deviation must be
recognized whenever a partially exposed pack
is used.
The image is reected by the mirror onto the
lm surface. the electronic metering system
determinesthe required exposure, and programs
the shutter opening and duration accordingly.
The incorporation of a mirror in tghe lens-to-lm
path necessitated by the nature of the lm. No
separate negative lm is employed. Instead,
the image appears as a direct positive. Since
the nal product is an opaque print, it is viewed
by reection. As a result, the mirror is needed
to reverse the image so that the nal print will
be properly oriented. This requirement, in
turn, dictates the use of the reectance type
viewing screen rather than a ground-glass type
transmission system.
Note that the lm surface is deplaced from
the Fresnel viewing screen by the thickness
of the viewing screen assembly. The correct
focal distance for both viewing and exposure is
properly maintened, however, since the surface-
coated exposure mirror is deplaced by the same
dimension.
During exposure, the light from the viewing
system must be prevented from striking the
lm. This is accomplished by a rubber light stop
adhered to the hinged Fresnel carrier. When
the Fresnel carrier moves upward, the light stop
blocks off light from the viewnder eyepiece.
As indicated by the foregoing description, the
viewing system is blacked out during the actual
exposure.
As soon as the exposure is complete the
mechanism returns the viewing screen to its
initial position and the picks feeds the exposed
lm to the spreader rolls. The rolls break the pod,
spread the developer, and eject the lm from the
camera.
As in orther Polaroid pack cameras, the picture
is developed ouside the camera. Unlike previous
Polaroid Land Cameras, however, there is no
negative to pell off and discard.
The SX-70 accepts a special 10-lamp ash bar
that plugs into a receptacle directly over the
camera lens. There are ve lamps in a rowon
either side of the bar which must be removed,
rotated and reinserted after the fth lamp has
been red (Figure 1-9).
Insering a ash into the ash socket closes
switch S2 in the socket. This action sets up the
shutter electronic circuit to permet ring of the
ash lamp. A follow-focus mechanism, coupled
to the lens focusing system arrests the shutter
blades at an opening related to camera-to-suject
distance.
NOTE : On early camera models, the light
measuring circuit remains active even with the
ash bar inserted into the socket. If the circuit
determines that there sufcient ambient light, an
exposure will be made without the ash. Cameras
with «P» conguration or later shutters, do not
have this light measuring feature in the ash
mode. Regardless of the ambient light level, the
circuits will re the ash when a ash bar is in
the socket (unless of course, the lamps have all
been used).
If the array has been exhausted, the shutter
will complete the exposure cycle without ash.
Maximum exposure duration is 30 seconds.
When the exposure counter reaches 0 (empty)
the camera will not re a ash lamp even though
unused lamps remain in the bar. The previously
discussed deviation associated with the exposure
counter is applicable to the ash functions. If an
unusedlamp is in position and if a partially empty
lm pack has been reinserted, the camera will
continue to re lamps after the last sheet of lm
has been exposed, until the counter reaches 0.
As each exposure is completed, the exposure
counter substracts one digit until the 10 exposures
have be made. The counter then indicates 0...
When this occurs, switch S9 is closed. Closing
this switch inhibits the ash and the exposure
timing. Since the counting cycle is initiated by
the insertion of a lm pack, the pack may not
necessary contain a full supply of lm. If, for
some reason, a partially used pack is removed
and reinserted, the top lm will be the dark
8. Developing the print
9. Exposures using ash
7. Completing the lm pack