Contax I ribbons

Many thanks Deklari, a very interesting site.

Regarding ribbon length on http://pangzhou.net/?p=2907 picture 4 the ribbon is described as 115mm when fixed.

On http://pangzhou.net/?p=2405 in the last picture the ribbon is shown as being 100mm when fixed, the measurement I have used.

Of course, with the 'help' of Google translation I may have misunderstood the website!

Erik,

I understand clutches now! A damascene moment indeed!

Thanks

Michael
 
Erik van Straten said:
Or the friction in the clutches is too low. You can bow the clutches a bit in the middle towards the ribbon. I did it with a screwdriver. Aki Asahi is too smooth. Worked on mine. This idea came from Brett.

Erik.
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Hi Erik,
It's worked on the three Contax II models I have replaced ribbons in as well (Aki Asahi, also, for clarity). But I hasten to add, I was prompted to try it by the many helpful posts various RFF members have made on the subject over the last few years.

I think it does make sense, too, when one considers the way the mechanism is meant to function at the higher speeds. Putting aside the intermediate and slower speeds for a moment, the reason the Contax shutter works at all with just one set of ribbons, instead of the more usual pair per curtain, is because, at the higher speeds, the required slit width is pre-formed when the camera is wound. How much further the second curtain travels along the ribbons, relative to the first, is dependant on which speed is selected, of course. At the highest speed (1/1250 in the case of the II/III) the second curtain rests only marginally further than the leading edge of the first. At 1/500, as the camera is wound the second curtain travels a few millimetres further. And so on.

Now, the slit having been pre-formed, the beauty of the Contax design is that (when all is well, of course) the exposure will never taper across the gate. But in order for that to apply, the two curtains have to remain stationery, relative to each other, until the second curtain caps off the lower edge of the gate.

To me, it makes perfect sense, then, that, if the second curtain is capping off the exposure partway across the gate (or even completely), this is happening because it's running down the ribbons to meet the first curtain. If the correct fit exists between the ribbons and the clutches, there will be just enough interference to effectively, cause the first curtain, the second, and the ribbons to traverse the film gate as a single unit. Which is of course exactly what is meant to happen, at the fast speeds. Naturally there might also be other causes. Eg if the first curtain spring is broken or compromised it seems, at face value, to make sense that the second curtain would also gain on it. But we're assuming for the sake of this discussion that it's a Contax in basically serviceable order with nothing sinister making it malfunction, yes?

This is my understanding of it operation at the high speeds at least. But, like all of us, I am simply a Contax autodidact, and defer to the wisdom of members who have been fettling these cameras for far longer than myself! ;)
Cheers,
Brett
 
Dralowid said:
Many thanks Deklari, a very interesting site.

Regarding ribbon length on http://pangzhou.net/?p=2907 picture 4 the ribbon is described as 115mm when fixed.

On http://pangzhou.net/?p=2405 in the last picture the ribbon is shown as being 100mm when fixed, the measurement I have used.

I also see this, it is quite confusing. Also I have re-measured old ribbons om my Contax I, it is 100mm (not a 4 1/2")
Click to expand...
 
Deklari, Great, so the 100mm length has more votes than most!

Brett, the camera was working before the ribbons broke but it was quite hard to advance. I will investigate further and report. As I said at the beginning, with a broken camera and no one to repair it that I can afford there is nothing to lose!

I have another Contax I (dimple) which when fired makes a strange quiet whimpering noise and nothing moves... It appears to be largely untouched and will remain so 'till I understand what is going on with the other. Mind you, without slow speeds it may be easier to understand.
 
Thank you, Brett, for this inspiring philosophy. At the moment I am quite happy with one Contax I that works perfectly (v4) and one that works good except for the "sports group" (v7). But I will experiment with my v5 when I'll have the time for it.

Yes Michael, I think so too that the camera is easier to understand without the slow speeds. I would love to have a Contax I with only high speeds.

Erik.
 
I may have found the problem and if I have it is fundamental and remarkably obvious.

When I start tensioning the roller, the two pulleys to which the tapes are attached tighten up nicely but the central pulley to which the first blind is attached, remains slack.

Consequently all that is happening when I release the shutter is that the second blind is shunting the first blind down and no gap is appearing. I assume the spring in the roller is broken (or maybe I should admit to breaking it)?

IMG_2828 by dralowid, on Flickr

So my questions are:

1) Has anyone dismantled this roller and what does it look like inside?

2) If the spring is broken, I assume I will need another...do I have to buy a Kiev?!

IMG_2829 by dralowid, on Flickr

Looking around inside the camera it looks as if many have been in here before, not a screw untouched, not a surface unscratched

IMG_2827 by dralowid, on Flickr!
 
Dralowid said:
Ah Ha! I don't know which camera this is from but it looks beyond me!

Screen Shot 2016-10-28 at 16.47.14 by dralowid, on Flickr
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I assume the spring in the roller is broken (or maybe I should admit to breaking it)?

Exact same thing happens to me today. Also I have same issue with Contax III in the past. I open the roller and central spring looks really bad. I try to fix it, but not luck.
Finally I have re-placed bottom roller from Kiev. My Contax III work fine after all. Now look like I have same issue with Contax I.
 
The Kiev roller fits into a Contax II, but I do not think it will fit into a Contax I. But when you can take out the small central spring of a Kiev roller there is a big chance that it will fit into a Contax I roller.

Erik.
 
Erik van Straten said:
The Kiev roller fits into a Contax II, but I do not think it will fit into a Contax I. But when you can take out the small central spring of a Kiev roller there is a big chance that it will fit into a Contax I roller.

Erik.
Click to expand...

I see.
I have removed bottom roller and ribbons. If i hold it and rotated the curtain a number of times around the roller I build up some tension. It tell me what central spring Ok. Looks like the central tension not good then I sett up every thing. If so, the pre-rolling ribbons around the roller will build good tension of top curtain but will not crate good tension for the central spring of the bottom curtain. It's correct? or I miss something
 
The central spring of the roller has to be tensioned with a screwdriver at the side. There is a pin that locks the tension with a cap that is fixed by two screws. That is the tension of the lower (first) curtain. The straps have "independent" tension from the rollers at the side. These can be tensioned by turning the straps around them several times before they go trough the clutches and are fixed to the upper curtain.

Erik.
 
Erik van Straten said:
The central spring of the roller has to be tensioned with a screwdriver at the side. There is a pin that locks the tension with a cap that is fixed by two screws. That is the tension of the lower (first) curtain. The straps have "independent" tension from the rollers at the side. These can be tensioned by turning the straps around them several times before they go trough the clutches and are fixed to the upper curtain.

Erik.
Click to expand...

If turning with a screwdriver (at the side), each rotation will sett both (top and bottom) tension right? I guess next question will be how to determine right tension?
 
In a Contax I there is only tension from the bottom, all the springs are in the bottom roller. The roller at the top has no springs.

The tension must be set at a minimum, but so that at all speeds the second curtain closes the gap completely (without hesitation).

Erik.
 
Erik van Straten said:
In a Contax I there is only tension from the bottom, all the springs are in the bottom roller. The roller at the top has no springs.

The tension must be set at a minimum, but so that at all speeds the second curtain closes the gap completely (without hesitation).

Erik.
Click to expand...

Thanks Erik, It is clear now. Will try more
 
Erik van Straten said:
The Kiev roller fits into a Contax II, but I do not think it will fit into a Contax I. But when you can take out the small central spring of a Kiev roller there is a big chance that it will fit into a Contax I roller.

Erik.
Click to expand...

It will be rally challenging to re-place central spring. It probable require removing a site spring too. It is complicated process, most difficult part will be tighten one end of the spring to the central bar.
 
Deklari said:
I try to draw the picture of lower roller and spring
One end of the spring were connected to central bar through the hole. Other end connect to the roller. Spring has two layer (or direction) of twisting. One layer close to the central bar was surrounded by another layer of the same spring. I hope it help (if you understand my accent):)
Click to expand...
 

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Fascinating stuff, I notice the only pictures I have taken of late have been of the insides of cameras!

To recap and make sure I have understood all this I will write it down. Please correct me where I am wrong on any aspect and fill in the blanks as necessary.

I have not yet dismantled the roller on my camera, there seems little point till I find a replacement central spring. I will only lose bits or forget how it goes together. It would however be good to understand how this is done without making a mess of the 'outer' springs.

Here goes:

The bottom roller has three springs.
The two outer springs act to tension the pulleys to which the ribbons and second blind are attached. Their springs are anchored on the pulleys and the other ends are anchored to the shaft inside the body of the roller (??? or to a sleeve that is anchored to the shaft???). Deklari's excellent drawing helps (thanks!) but I would like to see a bigger detail of the central part

The central spring which controls the tension of the first blind is anchored to the shaft and the central part of the roller (? somehow, help!??).

In the normal course of events all three springs are tensioned by screwing up the shaft and capturing it in the small fitting bottom left of shutter (seen from back). The three springs will then tension at roughly the same rate but remain independent allowing an element of balance which will help with very slight differences in ribbon length etc.

((NOTE: The tensioning process is different on the dimple Contax I but more of this another day))

Without dismantling the whole roller (which I guess will mean cutting my new ribbons) I have to assume the centre spring has broken. The chances of it having come 'undone somehow' must be seen as zero and I guess any fiddling with the spring will only make it snap.

For a solution I have one or two ideas as to people who may have the relevant bits in a box and there is always a Kiev but I would far rather replace the whole roller if possible which means looking for the remains of a dead Contax I.

So if a anyone can offer a step by step of dismantling the roller it would be a great help.

In the meantime I will put the camera back together so as not to lose anything and turn my attention and sledge hammer to my next project!
 
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