How to fix frozen iris in a Cooke Portrait Soft Focus Series II 8x10 13"?

Hi from Paris,
I'm Jay, following this forum since few years ago, and this is my first post:
I'm the owner of a Cooke Series II SF 8x10 and the iris is stuck! No way to turn the ring... It's stuck at f4.5 (maybe +1/3)
I don't want force it and I'm looking for any informations to fix it
Any ideas?

Thank you (and sorry for my bad English)
Attachment 145875

I am sure this is bad advice, but it works. I hope that your English abilities do not cause you to follow this wrong and mess things up!

This looks like the type of iris where the large ring is mainly decorative. The iris mechanism usually has two zones. The first is the interior, which is basically two holding rings, one with holes for iris pins, the other with slots for pins on the other end of the leaves to slide in, and the leaves with pins in either end. All of this inside stuff is usually quite loose, and is not lubricated. I haven't found it to be the problem, generally.

The other part is the massive external ring on the outside. The only connection this has with the internal mechanism is one small screw/pin that you will see somewhere around the periphery of the ring. It passes through the outer ring, through a slot in the lens casing, into a hole on one of the inner rings. The slot is for the screw to move through as the aperture is changed. The screw is merely a link.

The outer massive ring is usually threaded on by a very fine thread which is hidden when the ring is in place. It mainly has three functions: to hold the screw and to cover the slot the screw travels in; to give a place to engrave lens openings or the correspondingly opposite arrow, and to look and feel good.

Part of the feeling good part is the nice smoothly lubricated, slightly dampened feeling of a well greased joint. It feels like that because the hidden threads are indeed well greased. It's an important point that NONE of this grease is ever intended to work its way down the screw, through the slot into the loose and unlubricated works of the internal mechanism.

When this type of aperture mechanism seizes up, what usually has happened is that the grease on the external ring's hidden threads has become dry and dirty, finally locking up. The internal parts are probably still loose and happy.

Usually the ring threads on from the front of the lens, and the threads are under the front edge of the ring. Putting one single drop of a weaker, more harmless solvent, such as goof-off, at four places around the periphery of the front of the ring where it meets the lens body, and waiting, is often enough to with some time work in and loosen the mess so that you can once again turn the ring. This might be enough to satisfy you, and it may be permanent, but the real fix would then be to remove the small screw, spin off the ring (you wouldn't believe how many turns it can take, the threads are so fine!) and clean and replace the lubrication . . . with not a bit too much!

When you remove the small screw SOMETIMES that is all that's holding one of the interior rings in place, and the whole mechanism will fall apart (don't ask me how I know--a certain 90mm Leica Elmar comes to mind), and the orientation you hold the lens in while removing the screw will make all the difference in that. Also when putting the screw back in, there may be many choices of where to fit it to the internal mechanism, and if you don't understand what's going on, you may get that wrong. I would say that if you are not mechanically inclined, you do not want to mess with that screw. Also, if you bugger the screw, you will never find another one like it.

Your best bet is to hope that a couple of drops of solvent makes the whole thing better. If you think you like that and would like it even better DO NOT be tempted to start dripping oil in along that edge to lube what you can't reach. That's guaranteed to eventually drip down to the internals and you do not want that.

This advice is based on my experience with the usual type of old lens. It is not necessarily appropriate for this particular old lens.

The series II has the iris right at the back of the barrel. The design of the iris, as well as the detailed engraving, varies quite a lot through the years.

The source of the jam could be friction under the outer turning rim against the barrel. Moisture or perhaps a knock?
I would loosen and remove the rear lens cell and examine the condition of iris leaves first. Another posibility is to remove the tiny locking screw set deep usually in the external iris ring (BUT MAKE MARKS SO CAN FIND THE THREAD HOLE AGAIN) and move the ring slightly back and forth, as well as from side to side.
I would normally suggest something like WD 40 both places, but you will have difficulty in removing excess penetrating oil from the inside surface of the iris blades. It can be done by dismantling the front and removing the central -ve lens. But the correct installation is essential for the series II to work properly.

Steven, we wrote while each other was writing. Does my process above apply at all to this particular lens, which I have not seen and you obviously have?

I'm not a big WD40 fan. It goes places it shouldn't, and stays there, so I would beware of that. Some people don't care, but as a professional restorer of unspeakably expensive and historically important other things (violins--the multi-million dollar variety) I usually try to stay with the original intent and materials of the original design and maker, which precludes WD40. My own bias speaking there.

What you write seems sensible to me.
Ihave never worried much about penetrating oil when there is no shutter involved and we are talking about mechanisms that are inches apart and where glass surfaces are so easily cleaned. Drops, not spray!

Have suggested this be moved to DIY?

Oh, thank you for these replies.
I'll check tomorrow, as I 've already unscrewed front and rear cells... Iris leaves seem to be in nice condition

Hi, few days later, I've tried and followed your suggestion, put some drops of solveant, and then lubricantAttachment 146237 around the ring..
Result: nothing.
Arff
I don't feel enough inclined to unthread the very little screw and going further.
Maybe someone knows an address, here in Europe, to repair that mess?
I really appreciate your help

Yes you are right to be nervous about the tiny screw. These screws are often in bad condition and the slot may already be damaged in a previous attempt. A servicer must be prepared to bore it out and replace with a new thread and screw. I certainly would only attempt it on something I had bought well under the market value for the lens! A series II covering 8x10 is not a cheap item. The servicing is quite straightforward - apart from the locking screw!

However, it might be an idea to buy a new screwdriver which is the right size, see it if fits the screw slot well and turn - without a torque which would damage the slot. A little thin oil in the hole, left overnight, will increase the chances. Do unscrewing over a tray, as this sized screw becomes invisable in seconds.
Don't use an old screwdriver of doubtful dimensions and condition.

Quote:

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Originally Posted by jaytral

Hi from Paris,
I'm Jay, following this forum since few years ago, and this is my first post:
I'm the owner of a Cooke Series II SF 8x10 and the iris is stuck! No way to turn the ring... It's stuck at f4.5 (maybe +1/3)
I don't want force it and I'm looking for any informations to fix it
Any ideas?

Thank you (and sorry for my bad English)
Attachment 145875

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we wrote while each other was writing.
http://hautavis.net/128/o.png

Thank you for the clarification Steven.
I've mailed SK Grimes and I guess Adam will be the right person for repairing this iris.