Hi, Glenn --
I absolutely LOVE that lens (Zeiss Distagon 25/2)! It's super sharp, excellent for low light shots, and it has very low linear distortion. It's an excellent landscape lens for shots where you want a perspective "in-between" a super wide and moderately wide angle, without objects at the corners of the frame being distorted.
The vignette was intentionally added in PP. My idea was to give the appearance of a nosy neighbor peering through a hole in the fence to see what all the commotion was about. The "story" behind the photo was that a conservative businessman met a wild girl (as hinted by the leopard print thong panties) at a nighttime backyard party (as hinted by the umbrella in the "feminine" mixed drink), both had been drinking... and you know the rest. I intentionally left out some of the woman's articles of clothing to leave your imagination to fill in the blanks of what might have took place before they decided to get in the pool. I took this photo for a photo contest on another site, where the theme was "Wild." I thought the leopard thong hinted at the "wild" theme, as well as making one think of the term "cougar" to describe the woman. I thought the alligator float added some additional cartoonish humor and also hinted at the "wild" theme, especially since one of the red pumps is in the gator's mouth, as if to hint the gator might have eaten the woman. No, I didn't already have the panties, bra, pumps and pool float. I bought all those items (on sale) specifically for the photo.

I had to tape the gator float to the side of the pool wall to keep it still during the long exposure.