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Backscatter Neutral Density Underwater Filter System
Last Update: 26 January 2006 12:33 AM
7 comment(s)
Author: James Wiseman ( james )
This Article's URL: http://wetpixel.com/i.php/full/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
Ack! There goes that patentable idea ;).
One thing that I see could be an issue here is that the filter has the split at halfway across the element, and is round/mounted centred on the lens. This limits the compositional possibilities a little. I suppose I will just have to keep working on my plan to find a way to mount a rectangular ND grad in a cokin style mount to the front of a camera in a housing…
Posted by Craig Ruaux on 06/18 at 06:06 AMHi Craig,
Ah, too bad - you were beat to market! :-)
Using the same gear arrangement, it shouldn’t be too hard to mount a cokin or lee filter holder on the front. They you could do some experiments with sliding the filter back and forth moving the graduation around. As long as there’s room in your housing that is. If you give that a try, please make sure to post the results.
I ordered a Sing-ray .6 (2 stop) graduated plastic filter and I intend to cut it to fit into my circular polarizer or UV filter mount. It would be nice to know whether I should put the grad line down the middle, or off center.
Cheers
JamesCheers
JamesPosted by James Wiseman on 06/18 at 10:01 AMThis looks perfect for my Sulu sea trip next year, how much?
I’m using the Sigma FE as well, So this basically slips over the front of the lens like the hood?
Stu
Posted by scubastu on 06/18 at 10:48 AMHi Stu,
Actually it’s a lot more complicated than that. It needs to be housing specific, since the gear has to engage a zoom or focus control on the housing. I think Berkeley has designed some for Subal and some for the Titan. You should really call him and ask.
I’ve designed one for my Seacam housing using a focus ring for the 100mm USM lens but I’m having to get a slip collar machined for the lens.
Cheers
JamesPosted by James Wiseman on 06/18 at 11:03 AMThanks James, I’ll call Berkeley.
Stu
Posted by scubastu on 06/18 at 03:07 PMHi Craig,
Keep owrking on your over the front idea. Has great merit. Design one for Aquatica’s 8” Dome for me. (This I gotta see.. it would be huge!)
Maybe you can make it like a contact and just place it on the front, smooth out the bubbles and shoot the sun. When not in use, peel it off and put in your BC.
Voila!
Best,
Tim Rock
Posted by doubleblue on 06/20 at 10:39 PMHi - are there any news about that stuff?
Thanks
ClaudePosted by Claude on 01/26 at 02:33 AM