I'm thinking of using my 4x4 filters on a 360mm Schneider Symmar-S. The convex glass of the lens measures ~ 86mm which a 4.4 filter placed on top completely covers with room to spare. The lens is threaded for 120mm filters and my Cokin ZPro filter holder has 95mm threads. Do you think that a 120 to 95mm step-down ring would work?

Curiously there are a second set of threads close to the lens surface that is about 96mm in diameter and inset about 12.7mm from the outer threads. I had thought that this was for some kind of "center filter" but the concavity of the lens intrudes. The 95mm Cokin ring threads and the opening of the filters barrel appears to be an exact fit with it. Do you think using a holder120mm to 95mm step-down ring will work and not vignette?

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Thaomas