Keldan Ambient and Spectrum Filters Demystified
...and what they can do for you
By Kevin Palmer
Unlike many of the generic red filters out there, Keldan does not take the "one size fits all" approach to engineering their filters. Because, of course, lighting conditions are different as you go deeper and and vary with the color of the water. When you select a filter for your needs, you will choose the diameter of threads required (or select a gel for rear lens mount or specially designed WWL-1 filters), select blue or green water color and select the typical depth you will be working. The 4M depth rated filter is ideal for someone who is going to manually white balance while using the filter - a "daylight" balance should be able to be achieved in the 2-15M range. The 8M filter is best from about 6M to 20M and is also a better choice for someone trying to work with auto white balance. The deeper filters will remove more light spectrum - about 4 stops. That means they will require a fair amount of exposure adjustment for suitable exposures. If your camera gets "noisier" results at higher ISOs, it might be better to stick with the 4M filters
Like all filters for underwater, Spectrum Filters only remove colors underwater (as mentioned, stronger filters will remove more light, weaker filters less light), they do not add color. Unlike most filters, Spectrum Filters are designed to remove several spectrums of color - not just blue - based on extensive in-water analysis. The goal is to give each image maker the best chance for accurate white balancing. But keep in mind how they work: at 35 meters, they can't magically add color, all they can do is remove some of the colors present, so it is important to understand the limitations. Used properly, within their designated depth range, they can make quite a difference.
The Keldan Ambient Filter can be one of the most important tools in a wide angle shooters arsenal. The concept can seem odd at first: Why would I install blue filters on my beautiful high CRI Keldan lighting? The answer is not obvious, but it is a pretty simple in concept. So lets dig deeper.
When you are working close to a subject, following a specific fish or shooting macro, you want the most accurate color possible from your light which are generating all the exposure lighting in the shot. But when you are shooting open water wide angle of any sort, you always have ambient light in the background that is dependent on the depth, color of the water, intensity of the sun, time of day, etc.
If you white balance for subjects that are video light lit in the foreground, you will likely have a very unpleasing background and the shot will tend to look "artificial".
If you white balance for the background ambient light, your constant light subjects will tend to look very red.
So, what is the solution? Keldan Ambient Filters are designed to help match foreground and background color closely enough so that one white balance blends the artificially lit foreground and and ambient lit background for a more natural appearance. Subjects are lit and well defined in front, but the exposure looks seamless - almost as if no lights were used at all. Different ambient filters are designed to work best at different depths and with blue or green water, for the most appropriate lighting and white balance. They can be removed and replaced underwater if your lighting needs change.
The video blow is a useful demonstration of the benefits of shooting with Ambient Filters.
We have Ambient Filters and Keldan Lights available for rental. If you are interested in a test drive, let us know!