This photograph was taken near Bill Schwab's place up in northern Michigan. The vignetting was due to stacked filters (polarizer + light green) I was using to cut down reflections and bring up the submerged grasses. I was planning on cropping out the vignetted corners, but they seemed to work OK with the impression I got when composing the picture- a microcosm in this little stream.
Thank you all for your very kind remarks and suggestions. This spot was yet another beautiful gem around Bill's place.
Jerry, I drove out to this place with Jim (Gim) after Dan (Firephoto) mentioned stopping by it early in the morning. By the time we arrived, all the fog had burned off and the sun was popping in and out of the clouds.
I will have to invest in some gel filters in the future. Right now, all I have is a cludgey setup with a bayonet-to-threaded filter adaptor and filters stacked on top of that; I'm surprised more of the frame wasn't vignetted. Reminds us that sometimes happy accidents do occur.