Perplexing Korona Shutter (Model D)

[Mike in NY]

I have a beautiful little 4x5 Gundlach symmetrical lens mounted in a Korona shutter - a model D, I believe. The shutter's scale is B-T-I-50-1/4-1/2-1-2. The shutter works perfectly at B, T, and I. But here's the perplexing part: the scale pointer can easily be set at the faster speeds, but when the pointer is moved past 50, the trigger lever cannot be moved all the way to the right and cocked. At first I thought the shutter was stuck, so I took it apart last night and was surprised to discover that there is a little saber-like "arm" that seems to intentionally move into place as the shutter is moved past 50, to prevent the trigger from being moved all the way to the right and cocked. Then I wondered, maybe it's supposed to be that way? Maybe not all of the shutters were made to go that fast? That didn't seem likely, but neither did it seem like this little "arm" was working incorrectly. It's movement is very precise and firm. I didn't want to take the next layer of mechanicals apart until I got some feedback. Does anyone have any insights?

Thanks in advance!

[Jody_S]

I was working on one of those just yesterday. T-B: cock the shutter with the big arm on the top, then raise the lever to the left (looking into the front of the lens) as far as it will go. Trip the shutter with the rocker-arm thingy, and lower the lever on the left to close the shutter. When the shutter is not cocked, the ring should turn all the way to 1/4, 1/2, 1, 2 settings, with no resistance, when that lever to the left is lowered. Then, cocking the shutter should at the same time raise the lever. On yours the lever should be connected to a pneumatic cylinder I guess, mine is missing.

When I got the shutter, mine did the same as yours, ie I could not turn it to any position other than T or B. The circular ring/pointer that points to the settings has several grooves underneath, all the appropriate pins and such have to fit in the right groove or else it blocks. If you unscrew the small brass knurled ring around the lens and remove that pointer thing, you'll see the slots and it's pretty easy to see which pin is supposed to go where. If any of them don't move, then you'll have to do more of a clean/lube on the shutter (I did).

[Mike in NY]

Yes, it sounds like you had exactly the same issue. How do you remove the small brass knurled ring? My only turns about 45 degrees.

[Jody_S]

It's a retaining ring, it just screws on. Squirt it with some lighter fluid if it's resisting. There's a spacer underneath which may be part of the problem; the spacer ring is too thick (IMHO) and leaves too much play between the speed-setting ring and the pins that should engage in the back.

[Mike in NY]

Got it! Managed to unscrew it, and the little saber-like arm is tracking in the groove perfectly. Still perplexed! But I'm wondering if something is missing, because there's nothing to track in the other long groove. Hhhmmmm

[Jody_S]

There are 2 round brass pins, and 1 chromed lever with a protuberance. 1 of the brass pins doesn't actually go in a groove, it butts up against the stepped right-hand edge of the speed selector.

[Mike in NY]

Thanks Jody - your explanation helped me realize the pneumatic tube on the left side was frozen. It just needed a little twist, and now it moves freely up and down! Much appreciated!