Fotodiox Adapter for Nikon any good?

I wouldn't use any of the long lenses on the X cams on a tripod unless a lens foot is used for mounting to the tripod. Think of the massive pressure on the mount of the camera if it is mounted directly onto a tripod with no support for the lens. Your Sigma 150-500 probably has a lens foot (I have 50-500mm) so that would at least be safe to use (but focusing might be difficult). Your 70-200mm f2.8 is too heavy unless supported by a monopod and your left hand. (My 180mm f2.8 is 1/3 the weight and half the length.)

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The sky is full of holes that let the rain get in, the holes are very small - that's why the rain is thin.
Spike Milligan