I noticed something very awkward with my Sony A7: when using a vintage Nikon lens (any older manual Nikkor), with an adapter, and a very short shutter speed (1/4000th of a second), I get a very dark band in top of the image (picture 1). This happens only with short shutter speeds, if I choose a longer exposure, for example 1/400th, the banding is gone (picture 2). With the Zeiss 24-70 it is also gone. Anyone have any idea what could cause this?

I just found this last weekend - I was shooting with a Nikon 70-300 on my A7s at 1/8000 second and had exactly the same issue. I will post a photo later.

Here are a couple of images with the dark band - shot at 1/5000 sec. The band doesn't appear on pictures taken at a slower shutter speed. The lens was a Nikon 70-300 zoom with a cheap tube NEX- Nikon adapter.