A little technology
Repair is a profession...
It's also a passion
Very specific mechanisms
Foca is a French brand whose manufacturing lasted 20 years, from 1945 to 1965.
The producing company was: Optique et precision de Levallois (OPL).
These devices have very particular mechanics, exclusive to this brand.
Disassembly requires specific OPL / Foca tools used in the workshop.
PF3 - 1957
Disassembly
Disassembly is carried out in the following order:
1/ removal of the counter and the pressure spring. 1 x two-hole screw.
2/ removal of the cocking lever. 3 screws.
3/ removal of the screwed washer and the cover.
4/ removal of the rewind button.
5/ removal of the screwed hood fixing washer
6/ removal of the gear button. 2 needle screws accessible by lifting the button.
7/ removal of the cover.
8/ removal of the flash switches. 3 long screws.
9/ removal of rewinding.
10/ removal of the rangefinder. 2 short screws, 1 long.
11/ removal of the 6 exposure window fixing screws.
12/ removal of an internal screw on the film winding side.
13/ removal of two screws securing the exposure window. 1 screw on the rangefinder side, one screw on the mechanism side.
14/ removal of two screws securing the exposure window to the bottom.
15/ removal of the exposure window.
16/ removal of the depth of field indicator. 1 notched screw underneath.
17/ removal of the lens (separation at the infinity position).
18/ removal of the lens mount. 3 screws.
19/ removal of the lens lock on infinity.
20/ removal of the entire mechanical block from below.
21/ release of tension drums.
22/ curtain clearance.
23/ removal of the self-timer. 2 fixing screws, 2 washers, 1 screw on the drive.
Repairs
After dismantling, we can see that, if the curtains are still in acceptable condition, a previous intervention replaced the cords of the first curtain with a double sewing thread, glued with a Superglue type glue and reinforced with small pieces of tape black. this paltry reinforcement left whitish marks on the drum and the curtain…
The second curtain tension drum spring is broken. This is common when you use too much force to make a risky adjustment.
It is necessary to replace this drum and the cords.
After dismantling, we can see that, if the curtains are still in acceptable condition, a previous intervention replaced the cords of the first curtain with a double sewing thread, glued with a Superglue type glue and reinforced with small pieces of tape black. this paltry reinforcement left whitish marks on the drum and the curtain…
The second curtain tension drum spring is broken. This is common when you use too much force to make a risky adjustment.
It is necessary to replace this drum and the cords.
The curtain has been preserved.
The cord removed from the drum, (moistened with solvent to soften the glue at the fixing point), the metal support was moved aside to remove the sewing threads.
The new cord is made of “jade wire”, 0,5mm.
Cut longer than necessary, it was placed in the tiran which was then closed and the original settings redone.
The cords were replaced in the fixings at the correct length and glued.
The drum on which the first curtain is glued has been put under minimal tension so that the mechanism can operate. (video).
You can see in the last photo that the cord winding support is conical in shape, which avoids overlapping.
You must then change the defective drum of the second curtain.
Second curtains
The drum for the second curtain was salvaged from another Foca Foca PF 2B from 1953 in less good condition, the curtains being stiff and brittle.
Complete dismantling took 10 minutes, which is always easier when you know the procedure…
The drum was removed, but the cords and metal support were retained.
The second curtain of the appliance to be restored was unstuck and very carefully removed from its metal support.
A “very personal” arrangement was used to keep the curtain flat so that it could be glued to the metal support.
The two drums with the minimum tension allow the shutter to operate normally. (video in installation B).
A partial reassembly was then needed to adjust the running time of the curtains and set the speeds.
Curtain tension
Before adjusting the curtains, it is essential to lubricate the mechanisms.
Never over-lubricate, as this will not only lead to no improvement, but may even cause problems.
Foca mechanics do not require specific lubricants, but oils and greases that are not designed for micromechanics should be avoided. After lubrication, especially with fine oils, you need to switch on and off several times and leave the machine alone for at least an hour to allow the lubricant to diffuse.
I recommend extreme caution when tensioning curtains.
It is a serious mistake to believe that it is absolutely necessary to tighten a lot for the shutter to work correctly.
A medium tension is required, which in no case should cause rigid cocking.
The Foca tension springs are very thin and fragile.
This tension must be progressive, even if it seems tedious.
Tensions are made on each drum by 1/2 turn, and handling the stop springs is not at all easy.
For this Foca, the table below shows that the curtain tensions make it possible to obtain the most identical running times for each curtain possible.
This ensures that the slit between each curtain is even, so that it passes in front of the exposure window to ensure correct exposure.
Despite this, mechanical shutters, whatever the brand, do not make it possible to have, on the one hand, speeds exactly corresponding to the standardized speeds engraved on the buttons and, on the other hand, regularity of the real speeds of exhibitions. This is completely normal and must be within the manufacturer’s tolerance.
The rangefinder
It is also very French in design.
The basic principle is classic. The viewfinder is placed above the lens (which avoids too much parallax), composed of a double prism with a small semi-transparent mirror in the center which allows the telemetry image to be reflected into the viewfinder.
In the center, a second rotating optical element, which modifies the focus. It is connected to the optics by a short arm pushed by a spring, either with a fine square-shaped adjustment for fixed optics, or a roller for interchangeable lenses.
The third optical element includes a 45° mirror. It is this part which transmits the visible image to the center of the viewfinder.
The rangefinder is factory adjusted, and firmly sealed with a very thick varnish. In most cases, the rangefinder only requires simple cleaning.
Some very used ones have become opaque or the central image is weak or even invisible. (This doesn’t just happen to the Foca).
In this case, it’s really complicated to repair. Sometimes a “donor” can allow replacement.
You must intervene with the greatest caution, otherwise you risk completely destroying the rangefinder.
It is possible to change the return mirror, if it is “visibly” damaged, or to disassemble the viewfinder, remove the prisms, and after cleaning, reattach the prisms if the semi-transparent mirror is not destroyed…. If all goes well, reassemble and adjust the rangefinder which, I assure you, is not an easy task… The adjustments are sensitive to 1/10 of a millimeter.
The difficulties...
The table below shows that on these devices, especially if they are used, adjusting the speeds is very difficult.
Indeed, despite the most precise possible adjustment of the scrolling of each curtain, the exposure times are not linear.
Unlike other types of shutters, there are no independent settings for the speeds of 1/500 and 1/1000.
For example, screw-mounted Leicas with 1/500 and 1/1000 ”already” had independent adjustments for fast speeds. This made it possible to adjust the lower speeds and adjust the departure of the second curtain precisely for the two high speeds.
Therefore, on Foca, we have to make Cornelian choices. Either favor the slowest speeds or the fastest.
From experience, the choice of adjusting the nits excludes the correct functioning of the rapids.
I had almost new Foca in my hands, none of which were perfectly adjusted.
It must also be taken into account that at the time, amateurs used much less sensitive films (50 and 100 ISO) and that very fast speeds were little used, slower ones were preferred.
Also, this table shows two successive triggers at 1/40. The settings are not similar, both for speed and for curtain scrolling times. This once again confirms the influence of shutter mechanisms on exposures. (This is the case for all brands).
Another problem specific to Foca, the slow speed mechanism (1 to 1/25) is random. There is a small adjustment, but in 3/4 of the cases it does not work regularly.
Conclusion
To finish on this restoration, it is obvious that the renewal of the curtains would have been (perhaps) a good thing, but the ones in place did not require it. They were still flexible and made of modern materials. Why change if it’s still good??
Foca is a marginal and original brand given its cocking and shutter mechanics. and even his rangefinder.
If they have ”a bit of” the Leica look”, they are far from similar, it is not a copy as there have been many.
These devices have undergone significant developments, while retaining the basic principles of the first model.
The strong points are that it is robust, it can work for decades if we avoid, for example, keeping it out of use with the shutter cocked. This irreparably distorted the second curtain.
The weak points, curtains which harden, wrinkle and even crack and some very deteriorated optical glasses.
Foca repairs are not easy. As explained on this page, to reach the curtains, you really have to dismantle a lot.
Changing the second curtains is almost a specialty…
The 100% French brand
