Backscatter Neutral Density Underwater Filter System

At this month’s Seaspace convention, James Watt showed some photos during his Digital Workshop that he took in Indonesia using a new filtering technique that results in dramatic improvement in the appearance of the sun in the frame. The photos were taken using a system under development by Berkley white of Backscatter.com. I had a discussion with Berkley today about his use of neutral density filters to aid underwater photography. He has developed a system where this type of filter can be mounted on a fisheye lens and the camera housing’s zoom control can be used to position the dark part of the filter to help control the sunburst effect.

Sample photos taken by Berkley White showing how the ND filter is used to properly expose the sunball.

A neutral density filter is a glass or polycarb element that has some of the element blacked to block incoming light. They come in "hard line" and "graduated" types depending upon subject matter - the hard line models quickly go from clear to dark, whereas the graduated version has a smooth transmission from clear to dark. The filters are commonly available and come in different strengths, from clear-to-a-half-stop to as strong as clear-to-4-stops reduction in power. As an example, using a 2 stop graduated filter it would be possible to expose the foreground at f8 @ 1/250th, but knock the sunlit portion of the exposure down to f16 @ 1/250th.

A photo of the ND filter and gear assembly, courtesy of Backscatter.com

Berkley has been working on this filter design for some time, and says that he has not yet perfected the system, but hopes to do so soon. Shooting with the filter mounted also poses some constraints - for example, once it’s on there, you’re using the filter whether the sun is in the shot or not. Usually, the dark portion can be rotated around to a blue water area where it isn’t noticed. I intend to give it a try on my next dive trip using my Seacam housing, Canon 1DmkII and 15mm Sigma lens and hope to write a follow-up article for Wetpixel