Dallmeyer 14" lens problem

[Dan Dozer]

I'm not sure if this is really the right place for this, but here goes. I picked up a "project" lens recently pretty cheap - a 14" Dallmeyer Serrac. Glass is in very nice condition, but the lens was advertised as having the iris stuck in one position. Some moron before me tried to flood the iris with some sort of solvent to try to fix the problem, but that is clearly not the solution. There are a couple of the iris blades that have come off at one end and they need to be re-positioned. It doesn't look like a difficult fix. However, that doesn't seem to be a reason for the iris to be jambed. I purchsed the lens on the assumption that I might be able to dissassemble it and fix the problem.

I've taken everything off that appears to come of off the center barrel of the lens, and all that is left is a front and rear barrel and the iris in between. However, I can't figure out how to get it farther apart. The lens barrel is aluminum and the iris is brass. There are no screws or slots for a lens wrench. I can't get anything else to unscrew and I'm assuming that is what has to happen next. I've tried cooling the barrel in the freezer in case the two halves of the barrel are stuck - I know that happens some times with aluminum.

Anyone out there who has taken apart older large lenses who may have any more suggestions?

Thanks,

Dan

 

[richard ide]

Dan,
Your question reminded me of a lens I took apart about 25 years ago. I just took the front and back cells off to refresh my memory. The lens I have is a very old 500mm Apo Tessar. One very small screw on the outside of the aperature ring holds the ring on the outside of the barrel and extends into the ring the pins on the blades ride in. Inside next to the the ring the blades ride in is a split ring that has protrusions on the outside periphery (can't see until compressed and removed) the protrusions fit through slots in the barrel and engage a groove on the inside of the aperature adjustment ring. I seem to recall that it took a lot of fooling around to get it back together.
Hope this helps.

 

[Dan Dozer]

Richard,

Thanks for your reply - everything that you have described is pretty much the same on my lens. I managed to unstick the iris - it doesn't actually screw in, but the outside of it just slips down into the lens barrel and when I looked very closely, it was actually pushed in a little farther on one side than the other which had jambed it in place. When I got it in flat, then it appears that I can lift it out. Now I have to look at what happens when I start to take the iris out. Hope I can get it all back together again.

Dan

 

[Dan Dozer]

OK - I got the iris apart, cleaned it all up, and even got all the iris blades back in place and everything now works fine. However, in doing a little searching, I've come up with another question. This lens is an Air Ministry lens from Dallmeyer London. The F stop range only goes from F4.5 to F11. I've seen that goKevincameras has a 14" Dallmeyer Serrac that goes from F4.5down to F32.

Anyone out there know why they would have made some like mine that only go down to F11? I know that many of the Air Ministry lenses were used for aerial photography, so maybe this is why.

 

[epatsellis]

I've had several process lenses that were similar, a little time spent with a round file will gain you a stop or two more, depending on the iris mechanism, I've had some that would allow tremendous enlargement of the hole and others that would barely.


erie

 

[PHOTOTONE]

I've had several process lenses that were similar, a little time spent with a round file will gain you a stop or two more, depending on the iris mechanism, I've had some that would allow tremendous enlargement of the hole and others that would barely.


erie

I think the OP wants to go smaller, not larger with the iris. His minimum opening now is f11.

 

[epatsellis]

and by filing (and thus enlarging) the appropriate end of the slot the screw rides in, he can....


erie

 

[Dan Dozer]

and by filing (and thus enlarging) the appropriate end of the slot the screw rides in, he can....


Erie,

You're right and thanks for the suggestion - I hadn't considered that approach. I could probably decrease the iris opening by enlarging the slot some. I'll have to look at it and decide if the effort is worth it or not. After last night in working with the iris, I would never have considered doing that sort of adjustment to a lens. However, now that I know that I can easily talk things apart and put them back together (and it still works), I'm thinking that if I'm careful, I won't harm the lens any. It would be nice to get it down to about F32.

Since it only goes down to F11, I'm not sure if I will use it for landscape work or not. I'm wanting to check how this lens looks compared to the Heliar I have of the same size relating to portrait work. I believe that this lens is a Tessar type so it might be too sharp for portrait/people photography.

For what it's worth, I only paid about $30 for the lens, and now that the iris works, even at F11 I feel it was well worth the money I paid for it.