50/50 Photography (continued)

The second problem, uneven light distribution, is solved with a graduated neutral density filter.  Graduated merely means that the filter is dark at the top, becoming transparent at the bottom. When the two filters are combined, the photographer has the tools needed to create a successful 50/50 image.

In order to gain a full understanding of the 50/50 technique, there is still one more aspect that should be mentioned: virtual images. This phenomenon is especially important since it's applicable to all aspects of wide-angle underwater photography. Dome ports create the possibility of a virtual image when used in conjunction with a wide-angle lens. Simply put, there is a point at which "virtually" everything is in focus. Generally, the virtual image is somewhere about a foot in front of the lens (while looking through the viewer, just focus back and forth until you find it).