I am getting vignetting in the corners of my images.

Ensure you are not using a DC lens on a full frame or 35mm film camera. If your lens uses a petal type lens hood, ensure this is correctly fitted otherwise the hood outline will appear in the corners of the picture. If your lens uses a front cap adaptor ring to hold the lens cap in place, such as a fisheye or 12-24mm, ensure this adapter ring is removed.