Contax S2 shutter adjustment

I was reminded recently of a post I made, some years ago, on Rangefinder Forum describing the adjustment of the Nikon FM2 shutter (later used in the S2). I thought posting it here might be a good idea. It's been edited from the original to remove the Nikon references and change a few specifics based on more recent experience.

Note: Some of the pictures are of other, similar, shutters so may not be exactly as the S2 shutter but they serve to show specific features.

The S2 shutter is a mechanical shutter with speeds from 1 sec. to 1/4000 sec. plus B. The shutter was made by Copal and is a variant of the Copal square shutter.

The shutter curtains are timed by a cam rotating around a shaft driven by a spring. The spring has a small amount of adjustment to its tension. The position of the cam at which the second curtain is released is fixed but the position at which the first curtain is released is moved when changing speeds. This is the only method used to adjust between the top four speeds (1/500 - 1/4000 sec.). slower speeds use an escapement and a number of linkages to hinder the rotation of the cam and so decrease the shutter speed. The two curtains are driven by individual springs each with its own tensioner. Once the curtains are released, they travel independently and have no interaction.

As mentioned, the main spring has some adjustment which will cause the main shaft to rotate more or less quickly. This affects all shutter speeds but the affect is mostly to the slow speeds with minimal affect to the high speeds.

There is an adjustment that alters the timing between the release of the first and second curtains. This affects the high speeds with no affect to the slow speeds.

The curtain tensions can also be altered to increase or decrease the travel time but this isn't recommended.

Adjustments can be made with the shutter in-situ but the high speed adjustment is easier with the shutter removed from the camera. Note that the mirror box of the camera needs to be removed to access the high speed adjustment. 

Image 1 shows the main operating levers that cock and trip the shutter.

Image 2 shows the location of the adjustments.

Image 3 shows the location of the curtain springs and the slow speed escapement.

Check all the speeds before making any adjustments. Only adjust what is necessary which is usually just the high speeds.

If you need to, adjust the slow speeds first then the high speeds. Note that this is a mechanical shutter and the speeds will not be perfect. It's quite typical for the top speed to be a little slow. All the speeds should be checked after each adjustment and some compromise may be necessary to get all speeds to within acceptable limits. Note that the 1/250th always runs slow to ensure flash synchronisation is acquired.

The main shaft has a disk attached to the top with a number of slots in it. The end of the main spring sits in one of these slots. See image 4. To adjust the slow speeds, move the end of the main spring to a different slot to either increase or decrease the tension as required. I've found the fingers forming the slots get pinched together by the factory to stop the spring end from slipping out so the fingers need straightening first to allow the spring to be moved. A flat bladed screwdriver pushed between the fingers usually does it. BEFORE moving the spring, wedge the tip of a screwdriver behind the spring end so that, if it slips out of the slot or you lose your grip on it, it won't fully unwind.

Note: The disk on the top of the main shaft that has the slots in it has a slotted hole that fits over a matching raised part on the end of the shaft. In theory, it would be possible to remove the disk and refit it turned by 180 degrees. See image 5. This would allow the spring to be tensioned an extra half-turn. I've never had to do that but if a spring was particularly weak, it might be a solution. The screw holding the disk in place is left hand threaded so turn clockwise to unscrew.

To adjust the high speeds, identify the high speed adjuster. See image below. It looks like the head of a screw with a slot in it but it's only visible side-on and the slot may not be facing you so may not be visible. Because it's not possible to engage a screwdriver in the slot in the normal way, it's necessary to use the tip of a flat bladed screwdriver pushed sideways into the slot to turn it.

If the slot isn't facing you then you need a screwdriver with the tip bent 90 degrees to get into the slot.  Note that, usually, only a very small movement is required.

Just to reiterate, check all the high speeds after adjusting the high speed adjuster and check all the slow speeds after adjusting the main spring as a compromise may need to be made. The below image shows the typical speeds after adjustment. I fire the shutter multiple times at each speed and plot the highest and lowest values to check for consistency. This was a good shutter - you may not get the speeds this close to ideal. But they should be within the upper and lower limits (red and green lines). Note that 1/250th (flash sync speed) has it's tolerance all on the over-exposure side because, if it runs high (under-exposure) then cut-off may happen when using flash.

Shutter speeds - before and after service

An example of the difference a service can make to the shutter speeds of a camera - in this case, an RTS II.

Shutter speeds before service:

Shutter speeds after service:

And, although not the sole reason for the slow shutter speeds, this is the dirt, on the end of a slip of paper, removed from the shutter magnet which can cause the magnet to be slow in releasing the second curtain and cause the shutter speeds to be slow and, often, more erratic.

Yashica FX-3 Super 4000 anyone?

 I recently acquired a Map KF-M1 camera. Made by Phenix in China using a Yashica FX-3 chassis, it has a Nikon lens mount and a top shutter speed of 1/4000 sec. It's the same camera as the Kenko KF-2N which was clearly an attempt to create a camera with the same specification as the Nikon FM-2n. The Map version was made exclusively for Map Camera in Japan and, unusually, has no branding on it. There was another version called the Phenix DN66 sold in the Chinese domestic market.

I was intrigued how the top shutter speed was achieved. The Nikon FM-2n uses the same Copal shutter as the Contax S2 and I knew that shutter will not physically fit into a Yashica FX-3 chassis - I've tried it. The shutter is larger and has slightly different mounting positions. So, to find out how it was done, I had to get a camera. All the variants are rare and, if you do find one, expensive. But I found a KF-M1 in China. The seller accepted an offer but it still cost me nearly £190 with the import tax paid.

With the camera dismantled, first inspection of the shutter suggested it was the same shutter as is fitted to the Yashica Super 2000 (and many other cameras) but it has an extra position on the shutter speed selector. A check of the shutter speeds shows it is struggling to get to 1/4000 and the general shape of the test results graph is very similar to that from a Yashica Super 2000.

(Note: The upper and lower limits on the above results sheet are from a Contax S2 and are not correct for the KF-M1. They should be the same as the FX-3 limits below.)

It's not unusual for the Yashica Super 2000 shutter to be slow at the top speed but some adjustment will usually bring it into specification. I'll have to see if I can get the KF-M1 shutter closer to what it should be.

So it appears Copal produced a further upgrade to the 2000 shutter, which was itself an upgrade of the original 1000 shutter as used in the original FX-3. So I'm surprised that a Yashica Super 4000 never appeared if the shutter was available and could be fitted with no modification to the existing FX-3 chassis. Maybe it was because it would be competing with the Contax S2.

Now I need to decide what to do with the dismantled KF-M1. I don't want a camera with a Nikon lens mount. I could fit the shutter into an existing FX-3 Super 2000 or I could fit a Yashica lens mount to the KF-M1. The camera is quite well made and, unlike the Yashica with plastic top and bottom plates, the KF-M1 has metal top and bottom. The focus screen is the original Yashica one with the diagonal split prism, which I don't like, but if I change the lens mount I'll also have to change the viewfinder so that's not an issue. Whatever I do, the camera is unlikely to get a lot of use from me so if someone out there has an urge to own a Yashica Super 4000, get in touch and we can discuss.

Update: There is now a part 2 to this post at https://contax139.blogspot.com/2021/02/yashica-fx-3-super-4000-part-ii.html

A new 139 fault

There's not many faults on the 139 I haven't previously seen but I did find a new one recently. The camera had very inconsistent shutter speeds with variations of up to half a stop in either direction. The shutter speeds are often out of specification, maybe 50% of the time, but I've never before seen a 139 with such variations.

The problem was caused by a contaminated shutter magnet so the solution was quite simple - clean the magnet. It's something I do anyway if I service a 139.

The shutter magnet is not to be confused with the release magnet, which can also become contaminated but the symptoms are different. Here's a picture of the shutter magnet. The white plastic arm has a metal plate at the top which contacts the magnet face. This plate and the magnet face are the parts that need to be cleaned.

The more usual symptom of a contaminated shutter magnet is the shutter staying open due to the plastic arm staying permanently stuck to the magnet.

Is your 139 locked up? This may help.

The Contax 139 is an electronically controlled mechanical camera. 'Mechanical' in that all the physical operations are driven directly by operating the film advance lever or by springs that are tensioned by the same action. Those springs subsequently drive the mirror up, rotate the shutter main shaft, drive the shutter curtains and return the mirror back to its normal position - in that order. Without any electronic control, all the steps in the sequence will still happen if manually triggered. The electronics just introduce a delay between the release of the first and second curtains by blocking the release of the second curtain with an electro-magnet and so controlling the period the shutter is open for.

Sometimes the sequence might not complete, or maybe fails to start, leaving the camera in a blocked condition where it's not possible to operate the film advance lever and the shutter release does nothing. Here's some tips on identifying where the problem could be and what might be done about it.

The first step is to identify if the sequence has started and, if so, at what point it has stalled. This is done by inspecting the position of the mirror and the shutter curtains. Check if the mirror is up or down. Also check if the shutter is open or closed and, if closed, whether it is still cocked or not. The following two pictures show the shutter in both cocked and released condition looking at the back of the shutter.

Shutter cocked

Shutter released

Possible scenarios:

1. Mirror is down and shutter is still cocked.
The sequence hasn't started. Watch the data back LED located at the bottom left of the shutter (visible in above pictures) and press the shutter release. If the LED flashes, the most likely fault is the release magnet is stuck. The release magnet is a permanent magnet which holds the mirror mechanism in its cocked condition. To release the mirror, an electro-magnet, wound around the permanent magnet and in opposition to it, is energised so cancelling the permanent magnet field and releasing the mechanism. The face of the magnet can become contaminated causing the release lever to stick to it even when the magnetic field is cancelled. The solution is to clean the magnet and release lever faces. There is more information on this on my DIY page. If the data back LED doesn't flash, the release signal is not getting through to the magnet driver circuit. Most likely cause is the transfer switch but there could be other reasons. More investigation is required.

2. Mirror is up and shutter is still cocked.
When the mirror reaches its up position, the mirror mechanism triggers the shutter. See the bottom of the page for a description of the couplings between the mirror mechanism and the shutter. With care, it is possible to manually trigger the shutter.

Triggering shutter

If the shutter triggers, the shutter is not at fault and the problem is with the mirror mechanism. Most likely cause is the lever of the mirror mechanism that contacts the shutter release lever is seized due to corrosion of the snap rings holding the lever onto its pivot. Another possible cause is that the mirror has not moved up far enough to trigger the shutter. This can be caused by the mirror foam being too thick.

Corroded snap rings

If the shutter doesn't release even when manually moving the release lever, there is a fault with the shutter. It's possible something is blocking the shutter, such as a piece of broken film, so it's worth trying to blow any debris out of the shutter with a can of compressed air. Other than that, the shutter needs removing for investigation.

3. Mirror is up and shutter is open.
The first shutter curtain opens immediately the shutter is triggered. The second curtain is held by the shutter magnet. If the second curtain fails to close the magnet may be contaminated and the lever that releases the curtain is stuck to it. This is easy to check visually. See the 'Triggering shutter' picture above. The white plastic lever that is held in position by the magnet is clearly visible. In the picture, the lever is in its released position. If the magnet has released the lever but the second curtain doesn't close, there is a fault with the shutter. See previous scenario.

4. Mirror is up and shutter is closed but not cocked.
In this instance, the first thing to check is if the shutter has fully closed. Compare the shutter with the 'Shutter released' picture above. There may only be a millimetre of difference in the position of the shutter blades but that is enough to cause a problem. If the curtain isn't fully closed, it may be pushed upwards by pushing against one of the rivets. This may close the curtain and release the mirror. If this happens, the problem is likely to be the second curtain brake which can become seized, or very tight, and prevent the curtain from fully closing. There is information on my DIY page about this issue. If the shutter is fully closed but the mirror hasn't returned then the problem is likely to be with the mirror mechanism again as in 2 above.

5. Mirror is down and shutter is not cocked.
The sequence has completed normally.

Mirror box/shutter couplings

These pictures of the shutter and mirror box show the two points of contact between them. The green arrows show the coupling used to trigger the shutter and the red arrows show the coupling used to lower the mirror.

S2 Problems

I bought an S2 a few weeks ago from a dealer in Japan who described it as good condition but with a faulty meter. The fault meant it was a fair, though not necessarily cheap, price. I bought it with the view of fixing it and keeping it. On receipt, though, it was obvious there were several other problems with it. A few emails back and forth and the seller agreed my, much reduced, valuation of the camera and gave me a partial refund.

One of the problems was massively slow top shutter speeds. To do anything with the shutter usually means removing it and that means an almost total dismantle of the camera. Here's the camera now.

The shutter (top middle) is not intended to be repaired or adjusted. The manual says shutters come pre-adjusted and gives no information on how to adjust them. I've worked on these shutters before and have discovered the general principles of how to adjust them but the process is more art than science and this one is not cooperating. I might have to find a replacement.

Here's the shutter back in the camera for testing after one of my many attempts to get all the speeds to within specification.

I'll post further news of this adventure in camera repair as it happens.