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Olympus Pen F Technical Exploration

Subj: Olympus Pen F
Date: 7/8/00 4:38:26 AM Pacific Daylight Time
From: ethos@uq.net.au (Stuart Willis)

Olympus Pen F technical exploration

Way back in the late 70's when visiting Japan I sought to acquire one of
these little gems - but even in their country of origin they commanded
quite extraordinary prices. They were almost a cult camera.

So it was with delight that I recently managed to acquire for a most
moderate sum, a Pen F as with 38mm Zuiko and 50 - 90mm Auto-Zoom. The
lenses were crystal clear and near mint - while the body was quite
excellent. I soon found the camera had a handful of problems.

Firstly a manifestation of that awful Japanese self-adhesive cellular
foam mirror-buffer and general sealing strip material which, with age,
deteriorates into a black crumbly "gunk". At every mirror-wink the stuff
descended. And too there were fragments trapped between the fresnel and
the main prism. In the viewfinder it was not a pretty sight:-((

Secondly, the mirror had a propensity to lock in the upward position
following an exposure. Sometimes the mirror would actually close in
response to activating the film lever-wind /shutter cocking.

Thirdly, - with the 38mm standard lens attached, picture-taking never
progressed further than stopping down the iris. I found it necessary to
then remove the lens and, with a toothpick, further advance the camera's
onboard iris activator blade. No fault could be found in the lens mechanism.

Never having seen inside a Pen F, I decided to first tackle the
clean-up process in the hope that the cause of the technical
malfunctions might become apparent in the process. Close inspection
revealed that the disintegrating mirror buffer foam could be replaced
without any stripping of the camera. Simply, two 2mm wide strips are
glued to the top and bottom extension edges of the fresnel. But there
was so much "gunk" between the fresnel and prism that the camera would
have to be stripped anyway. So I addressed this at a later stage.

Removal of the camera's top plate revealed more of this 'orrible
self-adhesive-backed foam strip - as clearly to seal off the viewing
system from dust. But of course the foam itself was now the source of
contamination. Every vestige of that stuff had to be vanquished. It was
also apparent that the prism and fresnel assembly could not be detached without
removing the complete mirror-box as an assembly. Removal of the front
leatherette showed the entire mirror-box to be held by five countersunk
screws - slight loosening of which showed that the shutter dial was a
bayonet-key fit and need not be touched in any way. In order to
withdraw the mirror-box as a complete assembly, it is only necessary to
remove the ocular prism; the die-casting which contains a transfer lens
and mirror, and a single adjustable-length bar as visible under the
camera base.

At this point the fixed mirror, prism, fresnel, and reflex mirror could
be surgically cleaned and the mirror buffer strip replaced with cellular
neoprene strips. Deft use of a scalpel on "Wet-Suit" neoprene produces
slivers which will doubtless last a lifetime (of either the camera or
the serviceman - whichever comes first;-) And I always clean
aluminised mirrors by flushing them with with Shellite aided by an
artist's sable brush. (Shellite is a highly refined petroleum spirit as
containing no vomit-inducing additives).

Note that the horizontal top of the prism "isn't". The prism is in fact
cut with an approximate 5 degree downward slope toward the film-rewind
end of the camera. Before the mirror-box assembly is removed, this slope
gives one the impression that the prism is out of position - whereas in
fact it is not so.

The prism is held attached to the mirror-box casting firstly by a very
obvious spring and secondly by a little adhesive between its forward
side and the mirror-box frontplate. At the bottom the prism rests within
a brass bracket which need not be removed in order to withdraw the prism.

Now here comes the root of the technical problems which triggered this
technical exploration. The mechanical module which contains the lens
iris blade interface and the mirror activation, (the top side of
which is normally visible simply by removing the camera baseplate) can
now be unscrewed from the mirror box.

In sleuthing the possible cause of the malfunctions it is first
necessary to figure exactly what is happening within this module. When
the module is removed and inverted, all becomes much clearer.
It goes like this:

The total movement is analogous to a crankshaft as with continuous
rotary movement. The slider mechanism is not reversed by some ingenious
spring but rather is "driven" rearwards by this crankshaft action. But
the slider movement is interrupted by a latch by which the reflex mirror
is held closed. That latch is then released by a cam driven from the
shutter escapement. Thus the mirror is held closed for the appropriate
period as required by the shutter dial setting.

The horsepower for all this is provided by a single light gauge coil
spring - one end of which is attached to a driven brass gear as
activated by the cocking action - and the other end of which is attached
to the "crankshaft-drive". The latter is visible beneath the camera
baseplate as a small disc featuring radial holes - one of which contains
the end of the spring.

In short - that entire mechanism was as dry as a bone and as rough as a
bear's arse. The roughness was cause by the the stem of a spring being
displaced and becoming a wire sandwich between the sliders. Correction
of this followed by a good old wash in a cup of Shellite, blow drying
and application of a little Mobius clockmaker's graphite grease on the sliders
brought everything to pure silk. The various cams and latches on the
underside of the module were also relubed very sparsely.

The module should then be refitted to the mirror-box. This with the
mirror in the down position and taking care to ensure that the mirror
activating peg mates in the elongated hole on the module underside.
Before reinstalling the mirror-box it is a good idea to lube the main
cocking gears - but *not* those gears which actually drive the rotary shutter.

Reinstalling the mirror-box can be tricky in respect to the meshing of
the module's brass gear with the corresponding brass gear which is
currenty captive in the main camera body mechanism. Inspection
revealed that in response to the double-stroke film lever-wind, 24
teeth are advanced. The module gear also happens to have 24 teeth and
therefore the spring tension would be wound one complete revolution. My
tests were to prove that this amount of tension is insufficient from
rest. It is in fact necessary to pretension to the extent of eight more
gear teeth. There are two ways to do this.

a). With the film lever-wind uncocked, offer up the mirror-box to the
camera body so that the two mating brass gears are still not quite in
contact. Using a toothpick, advance the camera body brass gear
anti-clockwise to take up the slack in the spring - and then further
advance against the spring tension by 8 teeth. Then slightly move the
mirror-box to engage the mesh.

b) The tensioning as in (a) can also be achieved another way - after
simply screwing on the mirror-box. This by later adjusting the
tensioner through the camera base. BUT - that tensioner is secured by a
LHT light brass screw which I found to be to me "extremely" tight.
A very fragile screw, easily sheared and very difficult to find a
replacement if disaster strikes.
In my judgment, procedure (a) was safer.

In summary.

The aforesaid module must interface precisely with the shutter
escapement trigger otherwise the mirror may not unlatch. If the spring
torque is insufficient (ie inadequately pretensioned) there will not be
enough horsepower to drive the crank one complete revolution against the
mechanical friction/resistance of the module and the lens iris.
Conversely - if it is over-wound then the escapement cam may be
incapable of untriggering the mirror latch. Also there is a
right-angled plate on the front of the module. This is a stop for the
escapement bar. If it is but a few thou restrictive the escapement bar
might not quite unlatch the mirror. A little trial and error with
needle-nose pliers will soon find the correct position. Remember we are
referring here to an adjustment of no more than half a millimetre.

If the mirror locks up upon test - it can be released by manually
triggering the shutter escapement cam-bar by use of a fine mini-screwdriver.

After all of this - my initial technical problems did not instantly
After some half dozen test firings and manual triggering of the various
functions everything fell into synch. The initial faults were a
combination of high resistance sliders due to completely dried-out lube,
a displaced wire spring stem, and inadequate spring tension.

With the module the bench came a heaven-sent opportunity to hone the
edges of the iris-triggering blade. A couple of strokes with a
superfine oilstone also considerably improved the mating surfaces of the
original punched steel-plate cam levers as underside the module. This
is somewhat akin to blueprinting a racing engine and perhaps a "bit over
the top". But every little enhancement is to the good in what is
fundamentally a module which absolutely demands that everything is set
up with precision. It is a very particular little s.o.b.

A necessary modification.
My Pen F came complete with an Olympus flash-shoe accessory by which
leverage forces are imposed upon the black plastic ocular surround.
Indeed during the stripdown I was to find the ocular surround to be
cracked in two places.
So - after repairing it with cyanacrolate I applied some contact
adhesive the camera top plate and then firmly pressed the flash shoe
home. If a mounted flashgun gets a knock - there will be virtually no
leverage moment on the eyepiece. This does not in any way interfere
with removal of the camera top-plate.

I am no camera techie professional and this whole job took me 6 hours.
Given today's labour rates it is not difficult to see why such a camera
had obviously been discarded as beyond economic repair. As always - I
resolved never again to indulge in such adventures ------- until next
week.... when something new turns up ;-)

Stuart Willis
Sunny Queensland, Downunder.