Zeiss Flektogon f/2.8 Zebra Problem?

[burokas]

I'm pretty new to photography. I've recently purchased a Carl Zeiss Jena Flektogon f/2.8 lens, the Zebra kind, in an Exakta mount. I've also purchased a Kipon EXA-NEX adapter, in order to use it with my Sony NEX-5N camera. I'll try to explain the problem (and I'm not even sure if there is one), as best as I can:

Let's start with the f-stop ring set at 2.8 and the focus ring set at infinity. Now I begin to turn the focus ring clockwise, getting closer to the shortest distance of 0.18m. As the focus ring passes the 0.3m mark, it begins to turn the f-stop ring counterclockwise. Ever so slightly. By the time the focus ring is at 0.18m, the f-stop ring has turned to position f/4.

What's more strange is that the aperture blades are still in the fully open position (f/2.. Now I turn the focus ring counterclockwise, back to the infinity position. The f-stop ring remains at the f/4 position, but the opening between the aperture blades gets smaller and smaller until it corresponds to the f/4 position at the moment the focus ring reaches infinity.

Is this how this lens is suppose to work, or does it need adjusting? Any help would be greatly appreciated.

UPDATE: I took the lens apart, nothing seemed out of order. Very clean and almost like new. There are 2 metal tabs (stoppers), each held by 2 screws. One on the wall of the outer barrel and one on the side of the inner barrel. I loosened the screws and moved both of them over to the other side (1mm max travel).

Now when the focus ring is at 0.18m, the f-stop ring only moves one notch, from f/2.8 to f/(between 2.8 and 4 position). However, when the focus ring is at the infinity mark, f/22 no longer works. It still clicks into position, but it no longer gets smaller from f/16. The aperture blades stay in the same place, f/16 is now the smallest it gets.

I've examined the mechanism very carefully and it seems like the inner barrel needs to be rotated a bit. If (looking from the back of the lens) I can rotate it even 1mm counterclockwise, it should fix the misalignment problems. My question is, does this inner tube/barrel rotate and what kind of wrench would I need? The metal barrel right around the lens has two slits in it.

Thanks again for all of the help!

[sichko]

I had a copy of this lens some years ago. I can't remember all the details, but there is some interaction between the focusing ring and the aperture. I can't remember the physics but I think the idea was that you could meter at one focus position and the aperture would automatically adjust to compensate for the change in light as the focus was changed. One of the early 55mm Micro Nikkors had a similar feature but I think it was dropped when TTL metering became available. A search for "compensating aperture" might reveal more about the idea.

I can't remember enough about your lens to know whether or not it is working properly.