Light Sources

There are a countless number of light sources we can use to illuminate our subject.  From the sun to the moon and artificial lighting sources we use to chase away the darkness, each individual light source produces its own particular challenge.  Mixing light sources further adds to the mix.


Metal Halides
The photo to the right was taken under 20,000K metal halide (MH) lighting and white balanced in the camera using the Pringles WB method.  Under typical reef tank lighting, manual WB techniques become a necessity.

White Balance:  Even the best white balance sensors in today's cameras have a limited operating range from approximately 4,000K to 8,000K.  This means any source of light that has a color temperature outside of this range will not be detectable by the camera's auto white balance sensor.  Since our reef tanks are typically lit by 10,000K, 14,000K, and 20,000K lamps, the camera cannot cope.

The resulting image almost always has a blue cast.  There are several ways around this.  One technique is to use custom WB settings.  Using a gray card or color checker is the preferred method, since it reflects back all sources of light.  Therefore, if our tank has mixed lighting such as a 14,000K MH, 10,000K VHO, and actinics, all of which have different light intensities, the resulting blue cast is still neutralized.

Dynamic Range:  Metal Halide lighting emanates from a very intense source.  The result is the tips of corals tend to be brightly lit and the intensity decreases as you progress down the body of the coral.  This results in a large dynamic range on the main subject.  As such, pay particular attention to the blinky highlights to ensure highlight detail loss is kept to a minimum.

Many times, the tips may be properly exposed but the body appears too dark.  The best way to correct this is to add a reflector to reflect some of the incident lighting back onto the base of your subject.  This decreases the dynamic range of the subject, making a proper exposure and capturing of fine detail possible.

Although we can also correct the darkened areas in post-processing by modifying the curve characteristics of the image, noise increases in these areas as a result.  Again, for the cleanest image, it is best to take care of imaging parameters and setup before actually recording the data.

Support:  So, we light up our reef tank with a trio of 400W metal halides and think 1,200W of lighting is blinding.  But, step outside on a sunny day and look around.   Look at the sidewalk, look at white cars, go back in and look at our tank - it will appear dark.  As reefers we know that no matter how strong our lighting is, it cannot compare to the intensity of the sun in which the corals are accustomed to.

The same holds true of cameras and their exposure system. Cameras are designed for shooting under daylight (under the sun) type conditions.  Bring it indoors and shoot under artificial lighting and the camera needs more light to get a proper exposure.

The resulting lower shutter speed stresses the need for a good support mechanism.  Remember, as we get closer, the more detrimental the effect even the slightest movement during the exposure will have.

Use of even a cheapie $4 Wal-Mart tripod results in higher quality photographs than handheld shots.


Actinics

Shooting under actinic lighting is tricky at best.  The low wattage of these lights makes use of support a requirement, as any motion will cause the entire image to be blurry.  White balance is a nightmare and capturing details seems impossible. With actinic lighting, simply set the WB to daylight and leave the blue cast as part of the image.  After all, when we look at actinic lighting it appears blue, and everything under it appears blue as well.  Another technique is to shoot RAW if your camera supports it.  These shots were done in RAW format and white balanced manually in post (a technical way of saying, I winged it).


Since actinic lighting tends to be exclusively in the blue spectrum, it is very easy to blow highlight information in the blue channel resulting in a loss of detail.  This makes actinic shots look washed out.  The root of the problem is the camera trying to bring up the red and green channels to match the blue in an effort to achieve proper color balance.

To counter the camera, set -0.5 EV compensation.  In other words, underexpose by at least ½ stop.  This will help preserve detail in the blue channel.  Here is where evaluating individual RGB channels becomes helpful.  Looking at the luminance histogram, the image may appear properly exposed.  Evaluating the red and green channels may indicate underexposure.  But, look at the blue channel, and we will most likely see some, if not a fair amount, of clipping.  This clipping results in loss of detail in the blue channel.

If you can evaluate individual channels, keep an eye on the blue channel for the best results.

Flash

One way to overcome the WB difficulties shooting under reef tank lighting is the use of a flash.  A flash burst is second only to the sun in terms of light output.

The downside of using a flash is it illuminates marine snow.  It can also create areas too bright and too dark, resulting in part of the image being overexposed, while other parts are underexposed. 

Additionally, it tends to be directional - lighting is harsh and produces intense shadows.

On the upside, the flash is directional.  It can be used to direct light where it best suits the subject and composition.  This allows us to control the look and feel of our image. Furthermore, the increased amount of light the flash provides brings out detail, colors, and reduces noise in the image.  Since the flash also overpowers the ambient light, it becomes the main source of light.  This helps with white balancing, resulting in accurate color captures.

Properly used, a flash can yield stunning photos.

 
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