OLYMPUS OM-1 35mm Film Camera Instructions
- June 3, 2024
- Olympus
Table of Contents
OLYMPUS OM-1 35mm Film Camera
Front of the OM-1 “MO” after removing the speed-sensing and aperture sensing rings. “MO” stands for “motor drive.” A set of contacts at the bottom of the camera, next to the FP-sync contacts, signals the motor-drive accessory.
CHANGES IN THE CORD
COUPLING SYSTEM
The Olympus OM-1 launched the design revolution toward smaller, more compact
SLR’s. We reviewed an early model of the OM-1 in the May-June and July-August
issues of The Camera Craftsman. Since then, the tiny SLR has had its share of
success. Like everything else, it keeps undergoing modifications.
You’ll find most of the changes in the exposure-meter system. Olympus
continues to improve the cord-coupling mechanism, the system of rings and
levers behind the lens-mounting ring.
In the early models, a cam action relates the diaphragm setting to the
galvanometer. A cam, formed on the aperture-sensing ring, operates a cam
follower – the cam follower turns the cord-coupling disc. One end of the
coupling cord hooks to the speed-sensing ring, the ring that turns as you set
the shutter speed.
The model shown in Fig. 1 senses the diaphragm and shutter-speed settings
through a planetary-gear arrangement. A geared section on the aperture-sensing
ring engages the pinion on top of the cord-coupling disc. Turning the pinion
rotates the cord-coupling disc through the planetary gears.
The speed-sensing ring also gears to the cord-coupling disc. A two-piece
speed-coupling pinion sits over the post pointed out in Fig. 1. The upper
portion of the speed-coupling pinion engages the geared section of the speed-
sensing ring. And the lower section gears to the cord coupling disc through
the two pinions at the front of the lens standard.
Once you disassemble the mechanism as far as shown in Fig. 1, you lose the
timing of the planetary gears. However, you can note or scribe the timing
during disassembly.
Set the shutter-speed setting ring to 1/1000 second. Then, remove the lens
mounting ring by taking out its four screws. As you I ift off the shutter-
speed setting ring, be careful to avoid disturbing the speed-sensing ring,
Fig. 2. Also, watch for the I oose detent ball.
A slot in the shutter-speed setting ring keys over the tab on the speed-
sensing ring (just as in the earlier designs). But there’s no cord attached
to the speed-sensing ring – rather, the speedsensing ring engages the upper
section of the speed-coupling pinion, Fig. 2. As yet, you can’t see the timed
position of the cord-coupling disc. And removing the speed-sensing ring loses
the timing.
So, before removing the speed-sensing ring, take out the four screws holding
the decorator plate, Fig. 2. Lift off the decorator plate to uncover the cord
coupling disc, Fig. 3.
You can now see the cord-hooking slot in the cord-coupling disc, Fig. 3. For
reasser T’ by reference, scribe the position of the cord-hooking slot. Then,
lift off the speed-sensing ring.
Removing the speed-sensing ring allows the cord-coupling disc to turn
clockwise. Before replacing the speedsensing ring, just turn the cord-
coupling disc in a counterclockwise direction – until the cord-hooking slot
aligns with your scribe. Hold the cord-coupling disc in place as you seat the
speed-sensing ring at the 1/1000-second position, Fig. 3.
As with the earlier style, the speedsensing ring engages the speed-setting
gear, Fig. 4. Turning the speed-setting gear changes the shutter speeds. A
hole in the speed-setting gear identifies the 1/1000-second setting. The
timing hole in the speed-setting gear should face the front of the camera as
you seat the speed-sensing ring.
There’s one thing we especially like about the newer design – it allows a
convenient mechanical adjustment of the exposure-meter reading. Turning the
cord-coupling disc changes the position of the galvanometer. So you can retime
the cord-coupling disc to get a totalresponse meter adjustment.
Consider that the needle indicates the same amount of overexposure or
underexposure throughout the light-level range. Here, you can simply change
the galvanometer’s rotational position. As with the earlier models, there are
no variable-resistor adjustments.
For example, let’s say the needle indicates one stop underexposure – there’s
not enough needle deflection for the light conditions. You get the same error
under a bright-light condition as you do under a low-light condition.
Lift the speed-sensing ring far enough to disengage it from the speed-coupling
pinion. Then, turn the cord-coupling disc. Turning the cord-coupling disc
counterclockwise rotates the galvanometer further – that moves up the needle
to correct the underexposure reading. If the needle indicates overexposure,
turn the cord-coupling disc in a clockwise direction.
Because of the changes in the cord coupling system, three major parts won’t
interchange with those in the earlier design – the speed-sensing ring, the
aperture-sensing ring, and the lens mounting ring. In the newer style, the
aperture-sensing ring, Fig. 4, connects to the coupling cord (the speed-
sensing ring couples to the cord in the earlier design). And the lens-mounting
ring in the newer style has a bearing hole for the upper pivot of the speed-
coupling pinion, Fig. 2.
CHANGES IN THE EXPOSUREMETER CIRCUIT
Despite the major modifications in the mechanical-coupling system, Olympus
has made only minor changes in the actual circuit, Fig. 5. One of the changes
simplifies the circuit – there’s no longer a safety switch controlled by the
galvanometer. You’ll also note some differences in the color coding of the
wires.
Pulling the top cover reveals some other minor variations. As with the earlier
designs, watch for the loose backlatch spring and the loose washer over the
hot-shoe contact, Fig. 6. There’s one other loose part – the entire rewind
assembly.
The exposure-meter circuit board, Fig. 6, has a slightly different
configuration. Yet the connections are the same as in the model we originally
reviewed, Fig. 7. Other than the color coding, there’s only one change – the
safety-switch resistor on top of the circuit board has been eliminated.
You might also notice the change in the pentaprism retainer, Fig. 6. The
pentaprism retainer in the earlier models secures a pair of tension-type
springs on each side of the pentaprism. The sprin::is have so much tension
that the retainer can be difficult to remove and replace. There’s no problem
with the one-piece retainer shown in Fig. 6.
REPLACING THE GALVANOMETER
In our first article covering the OM-1, we didn’t describe the procedure for
replacing the galvanometer. It turns out you don’t have to replace the
complete exposure-meter assembly -you can get the galvanometer as a
replacement part. And replacing the galvanometer can be a fast repair. You
don’t have to disconnect any cords or distrub any timing.
How can you spot a defective galvanometer? The needle remains at the bottom
of the focusing screen (as seen through the finder). Naturally, you’d first
want to check the battery and the exposure-meter switch.
Then, disconnect the galvanometer wire from the circuit board (a blue wire in
the later models, a green wire in the earlier models). And measure the
resistance between the disconnected wire and ground. You should measure the
resistance of the coil -around 1.5K. If you measure an open or a short, you
can replace the galvanometer.
Remove the pentaprism by taking out the two screws holding the pentaprism
retainer, Fig. 6. Then, take out the two screws holding the hot-shoe contact.
The white wire from the hot shoe contact has a splice covered by a piece of
spaghetti. You might find matters easier if you unsolder the wire at the
splice. That way, you don’t have a dangling hot-shoe contact. Now, remove the
four screws holding the exposure-meter assembly (the two long screws also
secure the back of the mirror cage). And turn the exposuremeter assembly
upside down, Fig. 8. Notice that we’ve set the shutter speed to 1/1000 second;
at this setting, it’s fairly easy to reroute the coupling cord.
You don’t have to disconnect the coup Ii ng cord from the pu I ley /gear
assembly, Fig. 8. Just remove the two screws shown in Fig. 8. Also, remove the
screw holding the coupling arm to the film-speed-cam assembly, Fig. 9. Then,
lift off the entire pulley/gear assembly. You can now see the bottom of the
galvanometer, Fig. 10. A pinion on the
pulley/gear assembly engages the second slot between the teeth of the
galvanometer gear segment.
Spring tension turns the galvanometer housing in a clockwise direction. As
yet, you can’t see the galvanometer spring – it sits on top of the
galvanometer housing. But the spring may be loose a$ you lift the
galvanometer from the cam support. Take out the two screws that hold
the cam support to the top of the exposure-meter assembly, Fig. 6. Then, lift
off the cam support together with the galvanometer. Only the spring now holds
the galvanometer to the cam assembly.
lift the galvanometer slightly and allow the spring to turn the housing in a
clockwise direction – that lets off the initial tension. Then, lift out the
galvanometer housing. The spring should stay on top of the galvanometer, Fig.
11.
A new galvanometer comes with the wire already attached – but not with the
spring. So transfer the spring to the new galvanometer. On reassembly, slip
the upper end of the spring into the camassembly slot, Fig. 11.
Notice the post on top of the galvanometer, Fig. 11. This post must ride in
the limiting slot on the bottom of the cam assembly. Once you hook the upper
end of the spring, turn the galvanometer in a counterclockwise direction.
Turning the galvanometer counterclockwise applies the initial tension and
simultaneously moves the post toward the limiting slot. When the post reaches
the limiting slot, you should feel the galvanometer “drop” in.to position.
You can then reassemble the exposure-meter assembly.
When you’re at the stage of reassembly shown in Fig. 8, wrap the cord
counterclockwise around the galvanometer-control disc. Make sure the cord
passes between the galvanometer-control disc and the cord retainer. Then,
reseat the exposure-meter assembly.
ACCURACY ADJUSTMENTS ON
THE EXPOSURE METER
As mentioned earlier, the OM-1 doesn’t provide variable-resistor adjustments
for the exposure-meter accuracy. Yet, replacing the galvanometer may require
some adjustment.
Adjusting the total response normally isn’t a problem. We described one
technique – changing the timing of the cordcoupling disc. Another technique
you can use is to hook a pot in parallel with the galvanometer – between the
galvanometer-wire contact and the ground contact on the circuit board,
Fig.12. If you insulate the underside of the pot, you can leave it installed.
There’s plenty of room in the camera.
However, nonlinear readings cause problems. The fast-and-easy techniques just
provide total-response adjustments. If you find you have an underexposure
reading at a low light level and an overexposure reading at a high light
level – or vice versa – you may have to change fixed resistance values. As
with the earlier models, change R2 to correct the high light levels, change R3
for the low light levels,and change R1 for the middle light levels.