I've been testing placement of the camera and glass for a Martini shot using my new Venus lens and noticed that the glass was a bit dusty. I gave the glass a wash and that took care of the dust but There was still some water marks. So, after washing it three more times and even using some vinegar to try and remove those pesky spots, they're still not gone.
Looks like I need to apply more elbow grease and keep at it...
As Vinz mentioned, sometimes these modern lenses can be too sharp. 
I'm posting one of the test shots to show the bokeh this lens renders. It has 14 aperture blades and I like the bokeh it produces. This was taken wide open at f4 and is heavily cropped. The rim of the glass was about 8" from the front element of the lens.
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