I'm completely new to photography, and was attempting to shoot on a reflective surface (using a tablet for experimentation). I get some good results (to my untrained eye) but on my latest attempt, I get some weird shadow around my subject. I do not know the correct terminology to try and google the problem, so I figured I'd ask here.
If you notice the back edge of the battery, there is a shadowy (dark) spot that is more prominent near the top corner of the battery...
All shots are taken with a Nikon D3100, 60mm macro lens, F5.6 aperture, ISO 100, and a shutter speed of 1" (so that the problem becomes obvious).
This is a new shot of the problem. The slower the shutter speed, the more prominent the dark area becomes.
If I rotate the battery by hand, the dark area follows the copper colored side of the battery.
This is how my setup looks like (I followed a tabletop photography tutorial on Flickr):