First, let me restate that the intent is not to get an exact color match. I do not think it is feasible when mixing fluorescence photography with visible color light photography. This is more of an exercise in subjectivity than scientific accuracy. However, there is plenty of science involved. My main objective was to develop a recipe that I can use to take pictures, of my corals, that are a reasonably accurate color rendition of what one would see if one were at my house, looking in my tank, at my corals, in the evening, with the blue lights on.
Secondly, there are many ways to get to similar results in anything photography related so my way is only one of the many ways that the result may be achieved.
The first thing I did was to study about fluorescence photography and I learned about the Stokes Shift phenomenon, which basically states that fluorescence happens because fluorescent things reflect their color at the wrong frequency. This "shift" is what allows our camera to photograph something that is lit by UV light which most cameras can not see. The "shift" of color bumps the reflected color into the visible spectrum of the camera. Very blue light, near the UV spectrum, will also cause fluorescence and our cameras can see blue light, however, the color of blue we are using, is at the very far edge of the color that our cameras can work with. Working at this far edge of the color latitude is what causes color accuracy to be difficult and often visually inaccurate.
Another consideration is that not all cameras are created equal. My Samsung Note 4 camera can take pretty coral photos if gelled but there is very little hope of getting them to be visually color accurate to an acceptable level. In reality, the images made by my phone are more fantasy than reality, as the colors produced could easily mislead someone to think that an unobtainable color combination of a coral exists.
I tried using my wife's Canon 70D for a while because it has a cropped sensor which gives you more apparent focal length, effectively zooming in a bit more than a full frame sensor camera would. This camera is very capable but was not able to white balance as well as I would like in the blue color range. The reason is that this camera does not have the fidelity needed throughout its sensitivity range. It is a cheaper camera (sub $1k) and therefore uses a cheaper sensor and cheaper processor. It is a great camera and, like the Note 4 camera, can take beautiful coral pics, but is not up to the task that I was asking of it.
Finally, I gave up the extra zoom from the cropped sensor of the 70d and tried my 5DmkIII. Immediately I noticed that even without gels, I was able to white balance off of the blue lights and get accurate color. Too accurate actually. The white-balanced images were mostly devoid of blue, which is what one would expect. However, to visually match up the photo taken with the scene in front of you, I had to add blue back in via the WB Shift option in the camera's menu. As it turns out, I had to also shift toward magenta as well. This is likely to counteract the green light added by the Radions as I had them set.
That brings me to the lighting. I am using Radion X30 Gen3s. The lights are set to 20K on the Kelvin Slider in the Live Demo section of the Ecosmartlive App. I reduce the cool white to 0 and set the overall intensity to between 25 and 50% These settings are overwhelmingly blue but do have some green and red light mixed in. This seems to help non-fluorescent items (like my sun coral) render more accurately. I have these settings saved so that I can reproduce them easily.
While I was able to get reasonably accurate results photographing most corals with only white-balancing and WB shift, orange, pink and red corals did not render well with these settings. They tended to photograph more magenta than they look in person. Even if I took all the magenta out (by adding green in the WB Shift menu) they still did not look correct. I think this is just a result of working so close to the edge of useable color fidelity of the camera.
One way to move away from that far edge of color sensitivity is to gel the camera. To do this, I use Light Straw Gel (
#RS1111) made by Rosco. This helps to shift what the camera is seeing into a more useable range, helping the camera to be able to render the color more accurately. With the gel on, I white-balance as I did before by photographing a blank area of white wall above the tank, that is being lit only by the Radions. This reference image is what the camera uses to neutralize the color. As I did without the gel, I added Blue and Magenta back in via The WB Shift option in the menu.
This got me very close on everything. Greens, blues, purples are all pretty accurate. Red, oranges, yellows, and pinks still require some input based on each individual coral. I do this by examining the image and deciding if the coral needs more or less green and or red. Id make these adjustments in the WB shift Menu until I feel that the image on the back of the camera reasonably matches what I am seeing in the tank. It is unfortunate that this step is required but I think it is a result of warm color having a non-linear shift when fluoresced. This non-linear shift means that red is shifted more than greens or blues and the camera sees that differently than we do. The only solution is to adjust in camera and/or in post.
The included image shows just how far apart the two color spectrums are. While this is not likely the same issue that is causing the color inaccuracies in the orange range, it does show you how differently they react optically through glass and water. This chromatic aberration is caused by the fact that red light wavelengths are different from blue light wavelengths. This makes the two bend at different angles through glass.
