Polaroid SX-70 User Manual
A. GENERAL DESCRIPTION
I - DESCRIPTION
The Polaroid Land SX-70 is a folding, pocket
sized, single-lens reex camera which takes
and immediately delivers full-color pictures
approximately 31/4 inches square (see gures
1-1, 1-2 and 1-3). Operation is automatic; the
user merely inserts the lm, focuses and shoots.
power is provided by a six-volt battery inside the
lm pack; therefore, the batteries are always
fresh as the lm.
The four element lens has a maximum aperture
of f/8, and a focusing rang from 10,4 inches to
innity. The shutter is automatically controlled
by a photocell and electronic timing. Electrical to
mechanical energy conversion is accomplished
by two solenoids and a motor. There are no
separate diaphragm adjustement. The shutter
opening and closing time is controlled by the
exposure measuring system.
Figure 1-1 SX-70 Camera folded
Figure 1-2 Holding and opening the SX-70
Figure 1-3 Opened for picture taking
The subject is viewed and focused throught the
taking lens, a mirror, a Fresnel viewing screen
(with spilt-image focusing aid) and a optical
system to focus the image at the viewing eyepiece. As in all single-lens reex cameras, the
shutter must be open to provide an image at
the eye-piece. This requirement is fullled by
the automatic electro-mechanical components
which are described in detail in Section II of this
manual.
When the exposure is made, the image must be
transferred from the viewing system to the surface
of the lm in accurate focus. To accomplish this,
the shutter closes and the viewing screen swings
out of the optical path which is then diverted by
a mirror to the lm surface. These two paths
are described in greater detail elsewhere in this
section.
The exposure is made following the viewing
screen / mirror swing. The screen then returns
to the viewing position and the automatic
mechanism ejects the exposed sheet of lm.
development takes place outside the camera
and can be observed by the operator. As soon as
the print is ejected, the mechanism completes its
cycle to prepare for the next exposure. Following
thenth exposure, the ash circuit is inhibited until
a fresh lm is inserted. Normal operation will
resume when the camera is reloaded.
B. CAMERA OPERATION
The following paragraphs describe the electromechanical events that occur in normal operation.
the purpose of this desciption is to acquaint the
reader with the manner in which the various
functions are accomplished. Detailed analysis
at component / sub assembly level appears in
Section II.
1. Opening the Camera
When the SX-70 is folded, an interlock switch
(S6) removes all battery power from the camera
mechanism to prevent any drain from the lm
pack encapsulaetd batteries. To prepare the
camera for picture taking, hold the camera in the
left hand, pull straight up on the serrated portion
of the viewnder housing (Figure 1-2). this
action releases latches, which, in turn, allow the
main body of the camera to raise into operating
position.
When the camera is fully opened, the interlock
switch (S6), located at the left rear corner of
the mirror cover, is closed and the battery is
connected to the camera electrical circuit.
(Figure 1-4).
2. Loading the Film pack
The front coverlatchis located on the right side
of the camera just inside the rim of the bottom
cover assembly. Pressing down on this yellow
latch releases the front cover which drops down
to expose the lm chamber. With the cover open,
a lm pack can be inserted or an exhausted pack
can be removed.
A fresh lm pack is loaded into the lm chamber
observing color coding (Figure 1-5). Under
certain circunstances a partially used pack could
be inserted, but this action will cause some
deviation in the normal counting sequence.
The battery is a part of each lm pack, and the
two exposed terminals on the pack engage two
contacts within the lm chamber as the pack is
inserted.
Figure 1-4 S6 with contacts closed
3. Starting the Automatic Mechanism
With the lm pack in place, the front cover can
be closed. It must be fully closed and latched.
Figure 1-5 Inserting lm pack
Gears in the front cover must engage the main
gear train of the camera before the gear train
is put into motion. A switch (S7) located in the
forward section of the gear train compartment
initiates the application of power to the gear
train drive motor. Switch (S7) is actuated by two
components
(1) A projection on the front cover latch
(Figure 1-6 A), and
(2) A post on the right rear edge of the front
cover (Figure 1-6 B).
front edge of the front cover. The camera is now
ready to take the rst picture.
4. Setting the exposure counter
When a used lm pack is removed from the lm
chamber, the action automatically resets the
exposure counter at the rear of the camera to the
start position, closing S8. With a new lm pack
installed and the front cover closed and latched (
S7 closed), the motor is powered, and the dark
slide is ejected. The exposure counter turns
to number 10 (Figure 1-7), indicating that 10
pictures remain in the pack.
Figure 1-6 S7 contacts open and closed
Thus, the cover must be fulled closed, the gears
engaged, and the latch fully seated, in order to
actuate the drive motor.
As S7 closes, power is applied to the drive motor
(S8 is also involved and is discussed in a following
paragraph), the gear train is set in motion and
actuates a device called the lm pick. The pick
engages the dark slide, pushes it into the spread
rolls and the dark slide is ejected from the lower
Figure 1-7 Counter
5. Viewing and focusing
Viewing and focusing is accomplished through
a reect system (Figure 1-8 A). In the viewing
mode the image passes through the lens to a
xed mirror which reects it down to the Fresnel
viewing screen. The viewing path from the
viewnder eyepiece lens is from a parabolic
mirror and wafer lens, off the xed mirror to the
Fresnel screen. On most cameras the Fresnel
screen contains a circular split-image aera which
is used to focusing aid. A knurled knob (the
focusing wheel) on the shutter housing is rotated
to adjust the camera focus. The scene is in focus
when a vertical line within the split-image aera
is perfectly straight. On early cameras (without
a split-image feature), the scene is in focus
when the image seen on the Fresnel screen is
sharpest.
6. Viewing and focusing
The exposure is made by pressing the release
button. This completes the electrical circuit to the
Figure 1-8 Viewing and shooting
shutter to initiate a series of events. The shutter
blades close to cut off the optical path. The
hinged Fresnel viewing screen is swung upward
and comes to rest in front of the xed viewing
mirror (Figure 1-8 B).
The shutter opens and closes to perform the
exposure function.
A rst-surfaced taking mirror is fastened to
the underside of the Fresnel carrier assembly.
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 surfacecoated 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.
7. Completing the lm 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 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
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.
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 ash
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.
Figure 1-9 Inserting the ash bar
10. Closing the camera
When through using camera it be can folded and
latched in its closed conguration by pushing
the erecting link. When the camera is closed,
the interlock switch (S6) is opened so that the
battery is completely disconnect from the camera
circuits. The trim wheel (the lighten / darken
adjustement associated with the photocell)
automatically returns to its normal position each
time the camera is closed.
C. SHUTTER DESCRIPTION
(AMBIENT LIGHT MODE)
The shutter employed in the SX-70 camera is
unique. No direct comparisons should be drawn
between the manner in which it functions and the
function of other Polaroid electronic shutters. No
manually adjustable or xed aperture is employed.
When a picture is taken, two shutter blades, with
specially shaped cutouts, open the lens from a
totally closed position to a suitable aperture. The
two blades then reverse direction and again shut
off the optical path. These same two blades also
contain a similar (although differently shaped)
pair of cutouts that open and close the light path
to the photocell in like manner. In the following
description the functions of photocell cutouts is
deferred until the action of the shutter cutouts is
explained although in operation, the two functions
are interdependent.
When the camera is open for viewing, but before
the release button is pressed, solenoid #1 is
deenergized and the shutter blades are open. A
spring (openong spring) holds the shutter blades
wide open (Figure 1-10). The lens thus provides
maximum viewing / focusing brilliance. Solenoid
/ spring action is discussed in detail in the next
section of this manual.
Figure 1-10 Shutter blades held opened
When the release button is pressed, a switch
S1 closes (Figure 1-11 A and B) and applies
operating power to the shutter. As soon as power
is applied to the shutter, solenoid #1 is energized
and rapidly moves the shutter blades to the
closed position.
When the solenoid has reached the end of its
stroke (shutter closed, it no longer requires
maximum current to hold it at that postion.
Switch S4 (located on solenoid #1) closes (CB)
and activates an electronic circuit called the
POWER DOWN CIRCUIT. This reduces power
Figure 1-11 A Location & Arrangement of internal parts
Figure 1-11 B Operation
to an adequate level to hold the solenoid after the
high-current circuit has completed the solenoid
operating function and switches on the motor
drive circuit. Thus, the shutter will remain closed,
with minimum battery drain.
Light entering the lens is now cut off and the
reex mirror is swung upward to picture-taking
position. The electronic latch (activated by
opening S5) assures that the sequence will be
completed even if the operator removes his
nger from the exposure button, S1.
When the mirror swings up, a mecchanically
operated switch (S3) actuates a «Y» delay
circuit (40 milliseconds) (Figure 1-12) so that the
shutter will not function until the mirror bounce
has subsided. At the end of the delay period the
electronic circuitly removes the power from the
soleniod and the opening spring sets the shutter
blades in motion toward the full open position.
At the same instant an electronic switch opens
and starts the integration cycle. The integration
cycle is that period during which the total amount
of light (intensity and duration) reaching the
photocell is transformed electronically to regulate
the lenght of time the ml is exposed. The shape
of the opening in the shutter blades and the
motion of the blades is such that all of the factors
involved are continously variable throughout the
exposure period. this fact, however, is a design
consideration and should not confuse the theory
of the shutter operation from a maintenance
point of view.
When the camera completes all off its automafed
functions and the release button has been
released, all voltage is removed from solenoid #1
and the shutter opens in preparation for the next
exposure.
It should be noted that under extremeley low light
conditions, the shutter will closed completing the
exposure cycle in 14 to 30 seconds whether a
suitable exposure has produced or not.
C. SHUTTER DESCRIPTION
(FLASH MODE)
The special ten-shot ash bar is equiped with
a shorting bar so that when the bar is inserted,
two contacts within the camera is shorted. This
switch is identied as S2. When S2 is closed,
the shutter electronic circuit detects that a ash
bar is in place and ready for ring. In general,
the sequence of the functions remains the same
as for ambient light operation with the following
exceptions :
Figure 1-12 S3 Being opened by recock ram
mechanical device identied as the interceptor
connected to the lens focusing mecchanism
(Figure 1-13 A). the interceptor is moved as
the lens is focused regardless of whether
ambient-light or ash pictures are being taken.
When ash bar is in place (S2 closed) and the
gear train opens switchs S5 (Fighure 1-14),
solenoid #2 is energized and pulls the interceptor
into position to phycally restrict the shutter blade
travel (Figure 1-13 B). Since the interceptor is
controlled by the focusing mechanism, the
shutter opening is related to camera-to-subject
distance thus compensating for the ashbulb-tosubject distance to give proper ash exposure.
As a solenoid #1 de-energizes switch S4 moves
from the CB position to the CA position. This
switch conects VCC to the FFA.
When the ash delay period reaches completion,
the circuitry removes the holding current from
solenoid #2. Since the solenoid is an electromechanical device, removing power from it
causes a collapsing magnetic eld which induces
a y back voltage. This voltage pulse is fed to
the ash circuitry which then applies the ring
voltage across the ash lamp.
Figure 1-13 A Interceptor link, Solenoid 2, S2 operation - Solenoid de-energized
Figure 1-13 B Interceptor link, Solenoid 2, S2 operation - Solenoid energized
Figure 1-14 S5 being opened by the recock ram (Gear train)
In cameras with «P» conguration or later shutter
there is no ambient light measurement made. If
a ash bar is in the shutter socket a ash picture
will result regardless of the ambient light level.
On early cameras, an ambient light measurement
is made during the ash delay period. Since the
photocell aperture is a part of the shutter blades,
the amount of reected light reaching the cell will
also be a function of focusing distance. the shutter
electronics delays ring the ash lamp until the
shutter has opened to the aperture established
by the focus wheel. during this delay period, if
the ambient light level is sufciently high to cause
triggering of the integrating circuits, the exposure
will be completed and the shutter closed before
the ring voltage reaches the lamp and the lamp
will not be red.
At the ends of the ash timing interval, the circuit
energizes solenoid #1, the shutter closes, and
the sequence proceeds as in the ambient-light
mode.
If the bulbs in the ash bar are all used when the
operator attemps to make a ash exposure, all of
the previously described circuitly will function up
to the actual ring of the ash lamp. Since there
is no lamp to ignite, no ash ring current will be
drawn.
There will be no output signal from the ash
sequencing circuit, and an ambient light exposure
will be made. On cameras with «P» or later
conguration shutters, the result will be a black
picture unless the ambient light level is high
enough to give an exposure. this is caused by
the fact that «P» and later conguration shutters
have no integrating function as long as a ash
bar is inserted in the socket. Early cameras have
a twenty second time-out period even with a ash
bar inserted in the socket. Therefore, if the ash
bar is exhausted, a properly exposed picture
will result if the ambient light is great enough to
produce one in twenty seconds.
A. INTRODUCTION
II - THEORY OF OPERATION
A general description of the camera and the
sequence of its functions is contained in
Section I. In that section, detailed analysis of
individual assemblies and electrical circuits was
minimized so that emphasis could be placed on
the intenelation-ship of various functions. In the
following paragraphs, the individual groups of
components are described in greater detail. The
description are presented in the sequence in the
commponents were mentioned in Section I.
B. POWER SOURCE
Power for the drive motor, the shutter electronics,
and the ash array is supplied by a specially
designed 6 volts battery incorporated in each
10 exposures lm pack. When the pack is
inserted into the camera, two contacts pads
on the bottom surface of the pack engage two
spring-loaded contacts on the inner bottom
surface of the camera bottom plate. From these
two points, it is distributed to its destinations by
the copper foil strips of a ex circuit on the outer
surface of the bottom plate.
The battery has adequate capacity to expose
all 10 lm frames with at least six months of
expected shelf life.
C. LENS
The lens employed is a four element, glass lens
of f/8 aperture with a focal lenght of 115mm. It has
a focusing range of innity down to 10,4 inches.
Focusing is accomplished by movement of the
front element only. Helical threads in the lens
mount provide the linear lens elemet movement.
Operation is by means of a geared focus wheel
at the top of the shutter housing. There is no
manualy adjustable diaphragm associated with
the SX-70 lens.
D. VIEWING AND EXPOSING SYSTEM
When the camera is erected to picture taking
conguration, the subject can be viewed through
the collapsible viewnder. Figures 2-1 and 2-2
show the two optical paths in the camera. Note
the direction of the arrows. Reected light from
Figure 2-1 Viewnder optics (viewing)
Figure 2-2 Viewnder optics (exposing)
the subject passes through the camera lens and
is reected by the viewing mirror (on the inside
surface of the mirror cover) to the Fresnel viewing
screen.
The entire subject image is now reproduced
on the viewing screen. At this point, viewnder
optics must be employed for focusing. The optics
must transfer the image from the viewing screen
to the eye (done by the parabolic mirror and the
viewing mirror) and must present the image in
a fairly sharp contrast to permit proper focusing
(done by the eye lens and parabolic miror).
1. Fresnel (Figures 2-3 A and 2-3 B)
The special Fresnel (pronouced Freh-nell)
screen is employed to enhance the viewing
image by increasing the brightness and dention.
If a matte white surface were substituted for the
Fresnel screen, an image would still be visible.
However, the light rays striking nearest the
corners of the screen meet the screen at a more
oblique angle than the rays striking near the
center. At this greater angle, a larger percentage
of the light is dispersed and less light is returned
to the viewer. Thus, on a matte-screen image the
corners would appear darken than the center.
The Fresnel screen is designed to overcome this
problem.
The screen itself is a sheet of plastic upon which
are impressed series of concentric rings much like
the grooves pressed into a phonograph record
(Figure 2-3) instead of having a vee shaping;
however, the grooves in the Fresnel screen form
a saw-tooth with a tooth angle increasing slightly
with each successive groove in such a manner as
to complement the decreasing angle of the light
ray. The saw-tooth attens out completely at the
exact optical center of the screen. In the SX-70
camera, the optical center is not the geometrical
center of the screen.
increases the brilliance of the image within teh
viewing aera.
In summary, the Fresnel satises three conditons:
1 - it enhances focusing by distributing light rays
evenly across the entire viewing aera.
2 - it guarantees proper focusing by nature of its
acting as a ground glass - thus insuring that the
subject is in focus when the eye sees the image
in focus on the screen.
3- it acts as a reecting surface to permit the eye
to see the image through the viewnder optics.
The surface of the screen is silvered to provide
optimum reectance. The result is a brilliant
viewing image evenly illuminated from corner to
corner.
For the reader who is familar with the use of a
Fresnel lens used in conjunction with a groundglass focusing screen, or a Fresnel-ground
focusing magnier, it must be noted that these
are transmission devices while the Polaroid
screen is a reecting medium. Otherwise, the
brilliance enhancing properties are the same.
A suitable analogy would be the comparison of
a lenticular projection screen compared with a
matte surface. The ribbed surface of the lenticular
screen narrows the angle of reectance but
As show in Figures 2-3 A and 2-3 B, two types
of fresnel screens are used. Current types
(Figure 2-3 A) have a split-image circle cut into
the center of the screen which makes focusing
easier. Specially oriented prisms within the circle
split the image unless the camera is perfected
focused. Therefore, a straight vertical line in the
image aera would appear to be broken unless
the subject is in focus. To further ease focusing,
the image within the split circle appears brighter
than the rest of the Fresnel image. This is
possible because the split circle is not coated in
the same manner as the rest of the Fresnel. This
latter feature improves the ability of the viewer to
focus the camera in dimly lit aeras.
Figure 2-3 Fresnel screen
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