@willianaleman Sorry, but there is something wrong about that. If you use a Nikon to m4/3 adapter with aperture control there is no way that the iris will change during zooming. The adapter pushes the aperture pin to its maximum, the pin is locked to one side, it can't move anymore, the aperture is set to maximum.

If it changes for you, you have either a bad adapter or not the Tokina 11-16.

Psyco, " Sorry, but there is something wrong about that. If you use a Nikon to m4/3 adapter with aperture control there is no way that the iris will change during zooming. The adapter pushes the aperture pin to its maximum, the pin is locked to one side, it can't move anymore, the aperture is set to maximum." "If it changes for you, you have either a bad adapter or not the Tokina 11-16."

Psyco, I wish I was/I'm wrong because I like how wide the Tokina goes with the GH2 and how it will with the BMC, but the aperture issue was a turning point in my decision to return it. And, one, this adapter "Fotodiox Lens Mount Nikon to 4/3, http://www.amazon.com/gp/product/B001G4QXLE allows the operator to set any fixed aperture (not only to the maximum f/2.8) the lens has from minimum to maximum. Other cheapest adapters do not have these feature. Two, since the adapter doesn't have any electronic connection, I didn't expect to have any aperture changes until it happened. The Tokina has its own internal motor built in, called IF (internal focus) which works independently of the camera with the zoom ring, this is I guest what causes the issue.

the Nikon is half as wide. It wouldn't fill the same role at all for me. I too haven't experienced any aperture change on the Tokina I've rented in the past.

@willianaleman I still think there is something wrong with your lens. I don't have the Tokina here but I tryed it 2 weeks ago at a camera shop with a novoflex Nikon-m4/3 adapter on my GH2, and - really - the aperture can't change with this adapters.

The iris-pin on Nikon glas bypasses the normal (electronical) aperture control. It is pure mechanical and there is no way that the iris can change in that situation. How did you "see" that the aperture was changeing?

Also the Tokina 11-16 is regarded one of the best lenses that wide for under $2k. It only suffers a bit of chomatic abberation at the wide end. So if you see(!) strong distortion, you might have a bad copy of that lens.

@nomad I thought with constant aperture lenses, the aperture stays at the exact same diameter when zooming.

Isn't the F-stop a ratio between the diameter of the front lens and the iris? So with constant aperture and a front lens that can't change its size, shouldn't the aperture stay the same? (Maybe I'm totally wrong at that point.)

At least with my (very short) test at the camera store, I couldn't see any difference in brightness when zooming with the Tokina.

I'm going to have to agree with everyone here. I had this lens for a little bit and almost bought it again and it does not change aperture period. There's no possible way it can if you have a quality adapter on it. As stated before, it's an awesome piece of glass and the past two videos I've watched of Red footage, they both were using the cine conversion lens and it rocked! Once was from a mini helicopter. I did get a bad lens before from Samys so I think that's what's happened with the one you returned. At 11mm you're going to get a little softness no matter what.

I've used a tonne with manual adapters. It doesn't change aperture 'at all'. I'm afraid someone is either doing something wrong, seeing things, or has a faulty unit.

Psyco 5:19PM

"Interesting. Is this effect only with minimum aperture at f22?"

It does the aperture changes at other setting too, less noticeably because more light is passing through, but it is still there. And I don't want to have a lens that has to be in one fixed position all the time.

Now that many of you have seen the footage, we might agree that there is something wrong with the units and disregard that it is the adapter, because everything the adapter does is mechanical. I hope the footage can at least open the eyes to future buyers of this lens and I'd suggest that the constant aperture of the lens should be tested immediately after the purchase. Thanks again to all member here who have participated in finding a solution to the mystery on this "unit?"

@nomad 35-70 3.5 Minolta Macro beercan? Love that lens :) Secret gem lens - Leica loved it too :)

How does it compare to the Lumix 14mm f/2.5?

@psyco Have you pulled back the focus ring to put it in manual mode?

It's just a first guess, but I'd guess you're struggling to focus to infinity, which comes very quickly on a 11-16 lens. Only thing I could suggest, is get down to a local camera shop with some Nikon DXs in stock and ask to try a body out and say you've brought a few lenses.