Introduction: DIY Underwater Fluorescence Filters


Underwater fluorescence photography has become quite popular in the last 5-10 years.

In “Fluorescence for Underwater Research: Principles, Tools, Techniques, Applications and Discoveries” Charles H. Mazel defines fluorescence as “the phenomenon by which light is absorbed at one wavelength and re-emitted at another, longer wavelength. Many marine organisms contain fluorescent substances, and the right excitation light source can reveal surprising new colors and patterns.”

The technique reveals a hidden psychedelic world that we can capture quite easily and through this instructable, I would like to share a DIY approach to this technique.

The project assumes that you will already have an underwater camera with a housing and a strobe. My strobes are INON D2000. The sizing and positioning of the excitation filters could change depending on the make/model of the camera housing and strobe used. For example if the front port is smaller or larger diameter than the measurements listed in the design, you will have to adjust accordingly. I have provided details for using 2 strobes but you will only need 1 excitation filter if only 1 strobe is used. I have also included a design for an optional filter if a focus light is used.

Step 1: Supplies and Tools

For this project you will need:

  • Needle & Thread (I used fairly strong upholstery thread)
  • 2 sizes of bungee (~12 inches of thicker bungee, ~4 feet of thinner bungee)
  • 1 inch elastic (I purchased a whole roll as it was inexpensive ~$5-6)
  • 3x clips (one for each disk)
  • 7x cable ties
  • 2x excitation filters (dark blue) & 1x barrier filer (yellow), I used acrylic. (Optional, additional excitation filter for a focus light)

As this technique relies on the two filters (excitation and barrier), I would recommend spending a little time looking into the best options available. I was able to find a local plastic fabrication company who specialized in acrylic and custom work (signage, aquariums, etc). I submitted a simple design to them (photo 2) which had allowances for the diameter of my strobe and attachment slots cut out for the elastic webbing. The cost per filter disk was only $3-4 in total. In my opinion this was much cheaper and easier than trying to source the materials and trying to cut them myself. The disks came with a protective sheet which peeled off easily (photo 3). I have included an optional design for an additional excitation filter for a focus light if you find that the strobe focus lights are not bright enough (photo 4).

If you are unable to find a local supplier there are options available, like Ponoko, that can do the laser cutting to your specifications and design.

Step 2: Filter Assembly

Before starting, ensure that the protective sheets on the disks are removed.

  • Step 1: Insert a length of 1 inch elastic through the attachment slot on the barrier filter (photo 1).
  • Step 2: Fold the elastic on to itself (photo 2) and sew the elastic together using a needle and thread. I sewed across the elastic width a couple of times for extra security. Do not pull or stretch the elastic while sewing.
  • Step 3: Next, cut the elastic allowing for about 2 inches of elastic and some additional length to fold and sew over itself again, but this time sew the elastic around the thicker bungee (photo 3).
  • Repeat the first 3 steps for the other attachment slots.
  • Step 4: Tie the thicker bungee cord together in a ring with all the elastic tabs attached. Allow for a semi-tight fit around your camera housing port. I secured the knot ends of the bungee with 2x cable ties (photo 4, circled). Cut and attach a length of the thinner bungee for a tether, add a clip to the end in order to secure the barrier filter to the housing port. This tether will loop around the back of the housing and then secure to the thicker bungee. I used another cable tie to secure the knot ends of the tether (photo 4 circled).
  • Now that the barrier filter is complete, the process is repeated for the excitation filters. The only exception to the process is that the thinner bungee cord is used for both the inner ring and tether. The tether bungee length (with clip) will most likely be shorter as this only needs to go around the back of the strobe, not the whole camera housing (photo 5).

As per a suggestion by another instructable editor, there are other ways to join bungee cord such as crimp head clips or using glue-filled heat shrink tube for a neat join. You can lay the two strands out side-by-side so they overlap by 10-20 mm and glue it up with heat shrink tubing. Thanks Kai for the suggestions!

Step 3: Securing the Filters to the Underwater Camera Housing and Strobes

Attaching the filters to the camera housing port and the strobes is a relatively easy process.

The barrier filter is fitted over the front port (photo 1), the thinner bungee length with clip is wrapped around the back of the housing and the clip is secured onto the thicker bungee (photo 2). This secures the barrier filter to the camera housing. The same process is repeated for fitting the excitation filters onto the front of the strobes (photo 3 & 4), again using the clip to latch onto the thinner bungee. Once the filters are in place, you are ready to go for a dive and take some photos (photo 5).

Step 4: Image Processing

If your camera has the ability, I would suggest shooting in RAW as this will allow for the greatest post processing adjustments if needed.

After a dive, I transfer my images onto my computer and import them into my image processing program (photo 1). I use Adobe Lightroom as I find it very user friendly for the adjustments that I make with underwater photos. There are a number of options available such as Adobe Photoshop and even some free image processing programs (e.g. GIMP or RawTherapee).

I have used an example of a solitary cup coral.

The main adjustments I would make to an image would be exposure, shadows, and black clipping if needed (photo 2).

The final image can then be exported from your software (photo 3).

Step 5: Subject Selection

While there are a number of organisms which fluoresce, I would suggest trying to take photos of corals initially. I have found them to be ideal subjects for a number of reasons, including the fact that they do not swim away!

In my experience the corals will fluoresce differently depending on species (photos 1 and 2).

While underwater, I have had a chance to experiment with plenty of trial and error on different corals and other species such as fish, invertebrates etc.

Not all subjects will fluoresce but occasionally the filters can add an effect that you were not expecting and "happy accidents" can result (photos 3 and 4).

For additional information on underwater fluorescence techniques check out:

Underwater Fluorescence Photography

Fascinating Fluoro Photography

I hope you enjoy your DIY fluorescence filters and thank you for allowing me to share!

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