Contax I ribbons

[Dralowid]

Fear not, I am far from defeated!

Can't really see how it would be out of sync unless something happened when the ribbon broke.

What I plan to do is to release the tension (6.5 turns), remove the cover and, in the red group, feel for the point at which the second curtain releases, the simplest way of doing this would be in in B/Z at the point when one takes one's finger off the shutter release. If this is obvious then my problem may lie with the curtains sticking together. If not then something more serious is involved.

We shall see!

 

[Highway 61]

B (or in this case Z) can be selected.

When fired both blinds run down without the shutter opening.
The same applies to the other slow 'red' speeds.

The mid range 'white' speeds allow the shutter to move more quickly however the blinds do not open. The escapement can still be heard.

The fast range of speeds are only selectable occasionally and the shutter does not open.

The advance/speed knob may need to be wound past its setting and back when winding on.

Sounds like the ribbons are too long with the two curtains not separating from each other when you wind in full.

 

[Erik van Straten]

What I plan to do is to release the tension (6.5 turns), remove the cover and, in the red group, feel for the point at which the second curtain releases, the simplest way of doing this would be in in B/Z at the point when one takes one's finger off the shutter release.

It is very good to try to get the B (Z) working first. If that works everything is fundamentally OK.

When the tension is too low, at B (Z) the second curtain will not close completely and the first curtain will not roll up tight.

Erik.

 

[Erik van Straten]

Sounds like the ribbons are too long with the two curtains not separating from each other when you wind in full.

I am not sure this is right, but it is true that when the ribbons are too long the slit for 1/1000 sec. will be too narrow. The other speeds should work however when the ribbons are a little bit too long, they will only give a slightly shorter exposure.

Erik.

 

[Highway 61]

I am not sure this is right, but it is true that when the ribbons are too long the slit for 1/1000 sec. will be too narrow. The other speeds should work however when the ribbons are a little bit too long, they will only give a slightly shorter exposure.

Erik.

True.

The two curtains travelling closed can also be the result of an uneven speed of the first curtain due to the ribbons not enroliing themselves properly.

Or of the second curtain travelling too fast because of the ribbons not having friction enough at the sliding clutches point.

In any case, the culprit is a small detail hidden somewhere. Good luck and don't give up.

 

[Sarcophilus Harrisii]

It's an interesting comment about the ribbon length affecting the slit width, I've previously pondered this point, as far as I could tell, I also thought this may be one consequence.

It is sometimes said that these cameras should not be expected to actually achieve their maximum shutter speed. Notwithstanding other considerations like mechanical wear, adjustment or excessive friction, I wonder if a part of the reason for this may be the actual installed ribbon length being less than optimum for best accuracy?

When I did my first ribbon replacement to a II, my test film suggested slight underexposure, indicating the shutter was certainly not running slow. I used ribbons of precisely 5 inches length as suggested by Rick Oleson's notes. When I installed ribbons into another II (my third) on Friday night, because the ones in it were both intact (and I'm fairly certain, original) I took some trouble to break the stitching and remove them from both curtains intact instead of cutting them. Despite some fraying of the ends during the process of removing them from their slots at either end, both measured to within about a millimetre of 120mm which is slightly under the 5 inches (approx 127mm) I've previously used, and which has worked fairly well from what I've seen of films put through both examples. In the case of the II (& III) at least, there may be a tolerance of acceptable length ribbons as opposed to only one precise length, possibly? With the third one I worked on Friday night in which I installed 120mm ribbons it seems to be responding well at all the various speeds, but I've not yet had a chance to investigate it too closely.

Threads like this one are very interesting to me, because although some trial and error may be involved, the shared experiences of those of us prepared to work on our own Contaxes will hopefully add to the general knowledge of and understanding of these unique mechanisms.
Cheers,
Brett

 

[Erik van Straten]

Threads like this one are very interesting to me, because although some trial and error may be involved, the shared experiences of those of us prepared to work on our own Contaxes will hopefully add to the general knowledge of and understanding of these unique mechanisms.

Yes, that is also my motivation to share my experiences in trying to get a Contax I to work!

About the length of the ribbons: of course their length is very important - it is a German camera - but as long as I do not know how long exactly they must be, I have to try something. I think the shutter will work too when the ribbons are slightly too long (about 5 mm max.). In that case only speeds like 1/1000 and 1/500 will be a little shorter than they should. With the mechanism open you can see that the split changes when you turn the speed selector.

However, I can not get to work the 1/100 and 1/200 from the "sports group" really good - there is no complete exposure of the frame - so something else must be wrong (too).

Erik.

 

[Dralowid]

I measured the Contax I ribbons at 100mm or 3 15/16" using the old ribbons as a guide and taking into account fraying etc. 100mm sounds quite 'German'.

Bearing in mind that they were originally sewn by hand and that the two rollers have springs then I think some tolerance would be quite acceptable.

Today I have covered the camera with a cloth and we shall go out to lunch in a country pub. It would be unwise to attack it on my return!

 

[Erik van Straten]

Have a nice day! Beautiful wheather here too, but I have to work.

Erik.

 

[Dralowid]

I will get back to this in time but right now the weather is great and I'd far rather be out and about...with a camera.

 

[Dralowid]

So, back to this.

The issue is that the second curtain follows the first down without any opening.

My first thought is that the second curtain tension is too high in relation to the first.

The implications are:

That I got the number of turns of tension very wrong when undoing the camera

or

That I put too many turns of ribbon around the rollers before sewing

I will delve deeper but what concerns me is that the camera does not always wind on and cock the shutter fully. Sometimes I need to wind it on till it stops and then pull out and turn the knob a quarter of a turn to full cock the shutter.

 

[Dralowid]

Forgot to add...

After the shutter has fired the top or second curtain appears slighty 'loose' as if it is coming down too far(???)

This next bit I should have realised much sooner and is probably the key to the whole matter...

On further inspection, when wound on the camera does not come back to the speed setting it started at unless it is in the red group (slow speeds).

I will ponder further but it occurs tome that I might need to change the position of the second curtain on the top roller...maybe.

 

[Erik van Straten]

The issue is that the second curtain follows the first down without any opening.

That is my problem too, but only in the high speed group (when the tension is doubled). I found that the higher the tension of the roller, the more firmly the curtains "stick" together. There should be a slit between the two but there isn't.

Erik.

 

[Highway 61]

I will delve deeper but what concerns me is that the camera does not always wind on and cock the shutter fully. Sometimes I need to wind it on till it stops and then pull out and turn the knob a quarter of a turn to full cock the shutter.

Now, sounds like the ribbons are too short...

 

[Erik van Straten]

I will ponder further but it occurs tome that I might need to change the position of the second curtain on the top roller...maybe.

That is a dangerous operation as you can loose the synch of the gears. Only the second (top) curtain is connected to the gear train.

Erik.

 

[Dralowid]

Now, sounds like the ribbons are too short...

Or maybe wrapped round the rollers too many turns? my measurements were pretty accurate, I'd say within a couple of mm of the originals.

 

[Erik van Straten]

Or maybe wrapped round the rollers too many turns?

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.

 

[Dralowid]

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.

I don't quite understand what effect that would have. ?

If the clutch friction was increased wouldn't that encourage the first blind to pull the second blind down with it?

I need to open the shutter up again and see if I can understand this...I think I must be missing something.

 

[Erik van Straten]

If the clutch friction was increased wouldn't that encourage the first blind to pull the second blind down with it?

No, it works as a brake, it slows the upper curtain down. This is why the kind of ribbons is important. It should be a bit thicker and a bit rougher. Aki Asahi is too thin and too smooth.

What I did, was pressing with a screwdriver onto the clutch, a kind of throttling of the clutch. It worked, but not for the "sports group".

It seems that Zorki Kat found this. HU:Aki Asahi Ribbons for Kiev Shutters

Erik.

 

[Deklari]

I measured the Contax I ribbons at 100mm or 3 15/16" using the old ribbons as a guide and taking into account fraying etc. 100mm sounds quite 'German'.

I just measured old ribbons on my Contax I is approximately 4 1/4". I not sure if they are original or really works before (I currently get it on e-bay). I also check one Japanese web site (http://pangzhou.net/?p=2907) they used ribbons at 4.5"(115mm)

Also they have more information with pictures for Contax If (http://pangzhou.net/?p=2405)

P.S Thanks everybody for this topic it is really helpful. Thanks Michael for your pictures it helps a lot!