Problem with aperture ring on Cooke Triplet

[bc_69]

The aperture ring on a Cooke Triplet (barrel lens) I have received is siezed, it won't budge. First of all I'm not sure what causes this, and more importantly can it be fixed? There's no external sign of unusual wear, corrosion, dents or any damage, everything looks as it should but the ring refuses to move. I can remove the three glass elements no worries leaving just the part with the stuck iris.

Can anyone point me in the right direction to remedy.

BC

[bc_69]

I've noticed there are two small screws on the barrel just behind the flange. One appears to be locking pin, perhaps could be the one that moves the iris blade mechanism if it was working because I can see it through a small hole on the opposite side where the aperture turning ring would normally cover it and it goes through the outer ring into a slot in the inner ring. I've been able to remove the aperture turning ring without any problems, it just screwed off. The second screw which is to the side of the first one is sitting up higher and I can't see where it goes. Both can be turned with a screw driver but I haven't taken them out not knowing what they are for.

I've since read on this site that the series iia are noted for having this problem. This is a Taylor Hobson version lens, not a TT&H, with a patent number on the aluminium aperture ring. It is not a soft focus lens. The problem I've read is the grease on the thread of the outer ring has dried up causing the mechanism to seize.

My question is, will removing the screws allow me to remove the outer ring to clean and lub it again? Or is it more complex than that.

[bc_69]

Doh, stupid me, the aperture ring hasn't been removed, it is the problem and won't turn. I removed the front and rear elements.

I've decided to put a small amount of Zippo lighter fluid on the aperture ring thread to see if it loosens it up, no luck so far. The trouble with Zippo is it evaporates quite quickly. I need to find some of the stuff Jim Galli refers to in this thread on the same problem

http://www.largeformatphotography.in...ix+frozen+iris

[domaz]

The aperture might be seized because the blades have become undone from their pins or have bent. In that worst case the only thing to do is to remove the aperture ring (rotating ring that sits on top of the aperture blade) and reset all the blades one by one. You may possibly need to bend them back straight as well. I had to do this with a Cooke 150mm f/2.5 lens that came off a Graflex RB. Basically the aperture blades had bent and the pins had come out on some of the blades. I straightened the blades, and used "shaped" JB Weld in place of the Aperture pins. The aperture now works but it was a few days project to fix.

[bc_69]

The aperture might be seized because the blades have become undone from their pins or have bent. In that worst case the only thing to do is to remove the aperture ring (rotating ring that sits on top of the aperture blade) and reset all the blades one by one. You may possibly need to bend them back straight as well. I had to do this with a Cooke 150mm f/2.5 lens that came off a Graflex RB. Basically the aperture blades had bent and the pins had come out on some of the blades. I straightened the blades, and used "shaped" JB Weld in place of the Aperture pins. The aperture now works but it was a few days project to fix.

The blades look to be in pretty good condition, no sign of damage or pins missing, everything seems in order. The whole lens is in great order excepting the aperture ring is seized.

I'll give the solvent experiment a trial over a week to see if it moves anything. I've just noticed there are two small holes on the front of the aperture ring which seem to go into a thread, but because of their orientation on the face rather than on the outside of the barrel I don't believe they will be the correct entry point for the solvent. If that doesn't work I'll chance my arm at removing the tiny screws to see if I can get access to the area where the grease should be and hope it has simply dried up and there is no other internal damage.

[bc_69]

Can this thread be moved to DIY by a moderator please

[Jim Galli]

Get some of this stuff. Accept no substitutes. It leaves no residue and does not attack any phenolics. Hose her down. It'll free up but keep drenching it while turning it to float all of the ancient gook out. The gook will leave a residue but easily wiped off.

[B.S.Kumar]

Jim, I get an "Access Denied" response on the napaonline.com site. Is there any other place that sells it?

Kumar

[Jim Galli]

Jim, I get an "Access Denied" response on the napaonline.com site. Is there any other place that sells it?

Kumar

The one I know about is their proprietary brand. The active ingredients are hexane, heptane and acetone so the possibility is there is something similar but not that I have knowledge of.

[B.S.Kumar]

Thanks, Jim. Can you tell me the product name? I'll search for the MSDS.

Thanks,
Kumar