Weak spring in Compur

[SalveSlog]

I recently repaired a messed up 531/2 Super Ikonta. I even managed to get the rangefinder working correctly! That was more than I really deared hope for. But I believe the shutter has been tensioned for a long time, because the main spring is probably weaker than when new. This makes the 1/1 run slow at around 1.7 second. (The 1/100 runs fine, which I think tells me that when there is no resistance other than the basic chain from the spring to the blades, the spring is just strong enough to drive it.)

Attached picture shows the (same) spring from another similar camera/shutter that runs fine on all speeds. I could perhaps try moving that over to the Super Ikonta. But is it possible to shorten the original spring slightly to make it stronger? Is there a big risk of breaking it?

 

[RalphLambrecht]

I recently repaired a messed up 531/2 Super Ikonta. I even managed to get the rangefinder working correctly! That was more than I really deared hope for. But I believe the shutter has been tensioned for a long time, because the main spring is probably weaker than when new. This makes the 1/1 run slow at around 1.7 second. (The 1/100 runs fine, which I think tells me that when there is no resistance other than the basic chain from the spring to the blades, the spring is just strong enough to drive it.)

Attached picture shows the (same) spring from another similar camera/shutter that runs fine on all speeds. I could perhaps try moving that over to the Super Ikonta. But is it possible to shorten the original spring slightly to make it stronger? Is there a big risk of breaking it?

shutter springs have been tested in depth. Hasselblad determined that their lens shutters can be left cocked for 30 years or longer without losing functionality. A 1s exposure running for 1.7s is no issue; it might even compensate for reciprocity failure! I suggest leaving as is and congrats for fixung the range finder.

 

[Dan Daniel]

As Ralph says, 1.7 isn't that big a deal. Most likely the cause is dirt and such in the slow speeds escapement. Or the escapement mechanism needing to be adjusted. Faster speeds are often fairly close while slower speeds using the slow speed escapement show dirt and misadjustment.

I wouldn't move the spring. And I wouldn't try shortening the existing one. There is risk of breaking it if you try to cut off a loop and bend a new loop. Or you could bend the spring and put a crimp in it. Given the narrow channel it moves it, this is not good!

I would go shoot some film and see if the speeds are working for how you plan to use the camera.

 

[bernard_L]

What you show is called cocking spring in the official documentation. The main driver for actuating the shutter blades, with delay provided by the retard mechanism, is the main drive spring, 515 in drawing below.

Plus, if the "fast" (1/30 and faster) speeds are correct, there is presumably nothing wrong with the spring, otherwise they would be slow as well. I would rather look in the direction of the retard mechanism, maybe some dried lubricant.

Contrary to the prevailing expert advice, I would advise you to try repeated dips of the whole shutter assembly in renewed naphta, after removing the optical elements, of course. The reason being that the adjustment of the 1/15 speed is delicate, being very sensitive to the position of the business end (opposite to the pallet) end of the retard mechanism. Also, re-assembly of diaphragm and shutter blades, while doable, is a little tricky.

A sizeable fraction of experts seem to be of the opinion that a Compur can run dry. ((and now all the experts of the opposite opinion will start bashing my statement)).

I have a service manual for Synchro Compur (for Rolleiflex, but virtually no difference with Contaflex, so should be broadly applicable). If you need it send me a PM. Or, to give proper credit, download from:

Synchro Compur Service Manual - Matt's Classic Cameras

Synchro Compur Service Manual Synchro Compur Service Manual

mattsclassiccameras.com

 

[Ian C]

I’m not familiar with the escapement mechanism of that shutter. It would take a significant weakening of the spring that powers the shutter to make a big difference in the shutter-open time.

It is more likely that the overly long shutter-open time is a function of something other than the spring force, most likely friction and drag at the pivot points of the parts involved due to dried and oxidized lubricant. This slows the motion of the parts compared to their behavior when new and freshly lubricated.

Simply increasing the spring force is not a solution to the problem. A clockwork-type camera shutter mechanism has many pivots or bearings, each capable of introducing additional friction as the lubricant ages.

Here are articles involving various escapement mechanisms, both pendulum, and spring powered.

https://en.wikipedia.org/wiki/Escapement

https://www.roymech.co.uk/Useful_Tables/Cams_Springs/Escapements.html

A 1-second shutter time that has increased to 1.7 seconds due to a slowed mechanism gives a 0.77-stop exposure increase.

Cleaning out the old lubricant (and dirt if present) and relubricating with the correct lubricant should restore the shutter to normal operation. This is best left to an experienced camera technician (if you can find one).

 

[Ben Hutcherson]

Also, re-assembly of diaphragm and shutter blades, while doable, is a little tricky.

I have a #1 Synchro-Compur in pieces on my workbench now. This one was sticky at all speed and even the blade open button was touchy. It had never been my intention to go deeper than the mechanics, but I didn't realize I'd removed screws that allowed the blades to come loose.

I did manage to get the blades back in place and working smoothly, but getting them all back together and aligned properly seemed to at times need 3 or 4 hands. Removing the blades is something I usually try to avoid on any shutter.

(now I just need to finish cleaning the rest of it and get it back together...)

 

[Dan Daniel]

What you show is called cocking spring in the official documentation. The main driver for actuating the shutter blades, with delay provided by the retard mechanism, is the main drive spring, 515 in drawing below.

That's a Synchro-Compur shutter, bernard_L. A 531/2 Super Ikonta will have a Compur or Compur Rapid where the main spring is the same as the cocking spring on your diagram (much heavier spring).

Here's a guide to the Compur-Rapid shutter. The Compur will be basically the same without a booster spring-



If you go to page 23 forward, it talks about reinstallation of the escapement and adjusting speeds.

 

[SalveSlog]

Thank you all!

To bernard_L:

My shutter is not a Synchro Compur.

The front plate only says "Compur" but I believe it is an early Compur Rapid as it has that high speed spring seen under my index finger. The camera is probably from 1937. The main spring (or the "cocking spring" or "main drive spring" if you like), is the spring seen at 10 o'clock.

Regarding cleaning and lubing, I do think I have had quite good success with that, taking it apart all the way down to the aperture blades.

When the shutter is uncocked the cocking lever is not fully at it's relaxed/leftmost position telling me it must have lost some tension.
Also, cocking it takes noticeably less effort than other similar shutters of the same size. That's why I itch to try to shorten it...!

 

[BrianShaw]

As Dan mentioned, above, (EDIT: and someone else, too) the concern might be related more to adjustment of the retardant escapement.

 

[retina_restoration]

Thank you all!

To bernard_L:

My shutter is not a Synchro Compur.

The front plate only says "Compur" but I believe it is an early Compur Rapid as it has that high speed spring seen under my index finger. The camera is probably from 1937. The main spring (or the "cocking spring" or "main drive spring" if you like), is the spring seen at 10 o'clock.

View attachment 388261

Regarding cleaning and lubing, I do think I have had quite good success with that, taking it apart all the way down to the aperture blades.

When the shutter is uncocked the cocking lever is not fully at it's relaxed/leftmost position telling me it has possibly lost some tension.
Also, cocking it takes noticeably less effort than other similar shutters of the same size. That's why I itch to try to shorten it...!

The spring you are blaming for the slow speeds is not the culprit. It's the retard gear train.

As Dan mentioned, above, the concern might be related more to adjustment of the retardant escapement.

Yep.

 

[SalveSlog]

retina_restoration:
Please read what I wrote and believe me, there is no oil left on the blades.

 

[bernard_L]

I would rather look in the direction of the retard mechanism, maybe some dried lubricant.

As Dan mentioned, above, the concern might be related more to adjustment of the retardant escapement.

As the saying goes, one gives credit only to the rich.

 

[BrianShaw]

As the saying goes, one gives credit only to the rich.

I’ll fix that. But I doubt that he is rich. LOL

 

[bernard_L]

That's a Synchro-Compur shutter, bernard_L. A 531/2 Super Ikonta will have a Compur or Compur Rapid where the main spring is the same as the cocking spring on your diagram (much heavier spring).

I stand corrected.

This said, I was dubious of stories about springs losing tension. Because they operate below the elastic limit. Then I remembered my troubles with polymers creeping under stress. And a little googling taught me that creep (permanent deformation occurring slowly under a stress below the elastic limit) is also a reality with metals. Complicated stuff, depends on material and stress, of course, but also on temperature, etc.

 

[OAPOli]

How are you measuring the speeds?

I agree that you should clean the escapement. You can also adjust the 1 second timing by pivoting the escapement at the screw anchor point.

The cocking lever being sluggish could be an indication that there is some deformation. Is it moving smoothly when the spring is not anchored?

 

[Dan Daniel]

When the shutter is uncocked the cocking lever is not fully at it's relaxed/leftmost position telling me it must have lost some tension.
Also, cocking it takes noticeably less effort than other similar shutters of the same size. That's why I itch to try to shorten it...!

I would spend make a few adjustments to see if moving the escapement will bring times closer before tightening the spring. Also confirm that there isn't something in the way keeping the ring from going all the way home.

And if these fail, and you are intent on snipping the spring, be sure to cut and bend in a way that preserves the orientation of the loop, etc. If you don't duplicate the present orientation of the lopp, the twist to have it mount properly could cause a rotation in the spring that causes a problem. All in all there are many of these shutters out there so you will probably be able to find a new ring if this one blows up.

 

[bernard_L]

That's why I itch to try to shorten it...!

The 1/100 runs fine, which I think tells me that when there is no resistance other than the basic chain from the spring to the blades, the spring is just strong enough to drive it

On the 1/100 speed (and 1/30, 1/60), the main drive spring must move the shutter blades and overcome the inertia of the gear train in the retard (but without pallet). It is that inertia that makes 1/100 slower than 1/250. This is why I argued to leave the spring alone.

I wrote above:

Plus, if the "fast" (1/30 and faster) speeds are correct, there is presumably nothing wrong with the spring, otherwise they would be slow as well.

Let me correct this. Maybe you are right in thinking the spring is weak, and someone in the past compensated for this by adjusting the position of the retard. Because the retard lever travels less at 1/100 setting that at 1/60 or 1/30 (or 1/50, 1/25, never mind) the compensation should be less effective at these "slower fast speeds", where the fractional change of travel from the adjustment would be less. It would help to reach a proper diagnosis if you would post measurements of all speeds. A complete assessment of the situation is in order before making an irreversible intervention.

More generally. You have a working camera. And a nice one. Enjoy it. Take pictures. Resist the itch to make the last improvement. There is a risk with every intervention.

 

[SalveSlog]

Thanks for your careful considerations bernard_L!
But in my shutter it is the 1/100 speed that runs with no coupling to the gear train. The 1/250 speed is the fastest and is driven by the extra spring.

"More generally" you are right!! My perfectionism is certainly not always a blessing.

 

[bernard_L]

OK. So the retard is not involved in the 1/100. Just the main spring versus the inertia of the shutter blades. And you state that the 1/100 is correct within certain tolerances; so the spring is not that weak, is it?

The slow speeds involve the retard with the palette. As I wrote before, the 1/15 might be adjusted by moving one end of the retard to modify the depth of engagement of the retard lever (the one that comes against the hills and valleys); and such adjustment has little effect on the 1s, where the travel length of the retard is larger (say 15 times larger).

So what could cause the slow 1-second? Sluggishness of the retard. Did you clean the retard in naphtha? Did you lubricate it afterwards? I have possible evidence that lubricating the pivots of the gear train (watch oil, super-expensive swiss Moebius) slows down the retard; And definite instructions from Deckel (for the synchro-compur, admittedly) NOT to lubricate the pallet lever and wheel. Maybe (fuzzy memory) the 1-second can be adjusted by controlling the degree of engagement of the pallet; see for yourself in the manuals referenced below.

So at this point my suggestions are:

• Either us as is. Nice camera. I have the S-Ikonta 531, 645 format.
• Or, thoroughly de-grease the retard mechanism
  • Either in-place (frowned upon by experts)
  • Or after separating, but be ready, when re-assembling, for a delicate adjustment of the 1/15 speed and of the pallet engagement. A set of thickness gauges (used for old-style ignition contacts) might help.

I have two service manuals for the Compur-Rapid. One can be found there:

Camera Collecting and Restoration

The other (I believe) from National Camera; see below the top of the first page for ID. Send me a PM if you need that one.

 

[bernard_L]

Something else. You state in the OP that you adjusted the rangefinder. Beware, if you used a ground glass to check focus in he focal plane. On my S-Ikonta, I noticed that the pressure plate rests on the outer rails, a distance above the inner rails that is small but larger than film+paper thickness. I believe that the design relies on the natural curvature of the film (plus the two rollers) to keep it against the pressure plate.

Check your focus by taking a picture of a fence (closely spaced posts or chicken wire), full aperture, at an oblique angle, with a marker of the point where focus was made.

 

[SalveSlog]

I finally put a film in the camera and will certainly check focus.

My last shutter speed test gave this:
1/1 -> 1/0.5
1/2 -> 1/1.3
1/5 -> 1/4.6
1/10 -> 1/6.3
1/25 -> 1/13
1/50 -> 1/36
1/100 -> 1/93
1/250 -> 1/146

 

[Dan Daniel]

I finally put a film in the camera and will certainly check focus.

My last shutter speed test gave this:
1/1 -> 1/0.5
1/2 -> 1/1.3
1/5 -> 1/4.6
1/10 -> 1/6.3
1/25 -> 1/13
1/50 -> 1/36
1/100 -> 1/93
1/250 -> 1/146

The escapement could be adjusted for slow speeds 1/10 and slower, but the upper speeds are very typical. But unless you have a real need for the slower speeds being accurate, I'd go shoot the camera for a while and see what happens (simple to accommodate speeds being off with some minor math in the field). bernard_L is laying out the options and risks nicely of more work.

 

[retina_restoration]

The escapement could be adjusted for slow speeds 1/10 and slower, but the upper speeds are very typical. But unless you have a real need for the slower speeds being accurate, I'd go shoot the camera for a while and see what happens (simple to accommodate speeds being off with some minor math in the field). bernard_L is laying out the options and risks nicely of more work.

I agree with Dan. The amount of "error" in those speeds is practically insignificant. In fact, those speeds are probably close to what they were when it was brand new. Shutters from 75 years ago were rarely more accurate than what you're observing.
You can fiddle with the positioning of the escapement, but there's a very high risk that you'll end up with something far, far worse than what you've got right now, and not be able to correct it. Both ends of the escapement can be adjusted, but they each adjust different ends of the speed range. If you were to release BOTH ends at once, you'd have a right mess on your hands.

 

[Rumbo181]

Good evening.

Here is the table of my Retinas shutter speed. Usually I take out the escapement, clean, and reposition it on the base plate. Additionally very light layer of grease in pieces 514, 515 and 517: axes, spring and main lever. I don't think there are dry grease in the blades in any of them.

I think that a weak spring is to blame for the lack of top speed, as at 1/500 the escapement is actually not involved in action. At the end of the day, we are talking of 70 years old cameras.

In my opinion best course of action is let things as they are, all of them are taking very satisfactory pictures. However, I would be happy if I could get a handful of brand new springs.

On the other hand, the most you dive in the shutter mechanics, the most you admire the piece of engineering they are.

 

[BrianShaw]

That shutter, the SynchroCompur 00 (on your IIc and IIIC, at least) really is a fine piece of engineering. Those numbers are decent so your clean and lube must have been effective. I've never seen anyone confirm that the top speed ever performed at exactly the top speed. To adjust the faster speeds, though, the method involves making changes to the speed cam. That would be filing wider or swaging narrower the timing slot. Needless to say, that type of hand finishing could be quite time-consuming and, if not done right, irreversible. Your decision to just take pictures now seems a really good decision!