I take pictures inside boat cabins and rooms in homes to use in web ads. Many times it is quite dark, and sometimes the electricity is off. I use a wide angle lens, and the flash. But, in my pictures there is a big half moon shadow at the bottom of the picture. I think this is caused by my wide angle lens? What can I do to prevent this from happening. I know...the obvious...take off the lens, but is there another way? My camera (Olympus C-770) has a place to put another flash, and different flash modes.