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The image is reflected by the mirror onto the
film 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-film
path necessitated by the nature of the film. No
separate negative film is employed. Instead,
the image appears as a direct positive. Since
the final product is an opaque print, it is viewed
by reflection. As a result, the mirror is needed
to reverse the image so that the final print will
be properly oriented. This requirement, in
turn, dictates the use of the reflectance type
viewing screen rather than a ground-glass type
transmission system.
Note that the film 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
film. 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 viewfinder 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
film to the spreader rolls. The rolls break the pod,
spread the developer, and eject the film from the
camera.
7. Completing the film pack
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 flash and the exposure
timing. Since the counting cycle is initiated by
the insertion of a film pack, the pack may not
necessary contain a full supply of film. If, for
some reason, a partially used pack is removed
and reinserted, the top film will be the dark
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 film in the pack. This deviation must be
recognized whenever a partially exposed pack
is used.
8. Developing the print
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.
9. Exposures using flash
The SX-70 accepts a special 10-lamp flash bar
that plugs into a receptacle directly over the
camera lens. There are five lamps in a rowon
either side of the bar which must be removed,
rotated and reinserted after the fifth lamp has
been fired (Figure 1-9).
Insering a flash into the flash socket closes
switch S2 in the socket. This action sets up the
shutter electronic circuit to permet firing of the
flash 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
flash bar inserted into the socket. If the circuit
determines that there sufficient ambient light, an
exposure will be made without the flash. Cameras
with «P» configuration or later shutters, do not
have this light measuring feature in the flash
mode. Regardless of the ambient light level, the
circuits will fire the flash when a flash 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 flash.
Maximum exposure duration is 30 seconds.
When the exposure counter reaches 0 (empty)
the camera will not fire a flash lamp even though
unused lamps remain in the bar. The previously
discussed deviation associated with the exposure
counter is applicable to the flash functions. If an
unusedlamp is in position and if a partially empty
film pack has been reinserted, the camera will
continue to fire lamps after the last sheet of film
has been exposed, until the counter reaches 0.
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