Underwater Photography with HMI / HID Lights
Michael AW
HMI
technology is not new. Evolved in the late 1960s, a lamp
developer Osram began producing HMI bulbs for the film
industry at the request of German television seeking a
less expensive alternative to incandescent lights.
Ironically, HMI is now much more expensive than halogen
and tungsten. Though the principle behind the HMI /HID
lighting has been known for decades in the movie
industry, it was only in 1996 that I first saw them used
in underwater photographic application by David Doubilet.
Using two 1200 watts units, he created never seen before
pictures of fluorescent corals, mantas feeding at night
at Kona and atmospheric imagery of the Chandelier cave
in Palau. I was immediately hooked on the idea of using
a continuous light source that illuminates at day light
temperature – 5600 Kelvin like that of an underwater
strobe or electronic flash.
Watt for watt, Hydragyrum Medium arc - HMI' lights are
two to four times brighter than their tungsten
equivalents. Their application has revolutionized the
motion picture photography in films such as the Abyss,
Titanic and IMAX production of Volcanoes of the Deep
Sea. Since no filament is used, HMI lights are much more
robust and less sensitive to shock and vibration.
Generally the unit uses separate electronic ballast to
regulate power input and they are the lights of choice
for ROV in deep sea documentary productions. Until the
last few years, those used in the movie industry were
huge units of 600 watts to 2500 watts requiring surface
supplied power thus logistics and the cost of rental
precluded the use even by professional underwater
photographers. However with the demand of underwater
video makers, a few innovative German manufacturers have
started to produce units in the range of 24w to 100w.
Albeit the extraordinary illumination quality, the
principal draw back of HMI application is its cost.
Whereas a 50w halogen light costs less than USD300, the
24 watt equivalent HMI costs in excess of USD 1500. So
with prices like these, why bother with HMI? During
the last few years, I have experimented with the big
‘guy’s 1200w rented from PANAVISION for the 24-hour
shoot in the Maldives, 50w units by Treble-Light and
most recently the 24w Solaris Pro from Keldan. Each of
them serves the application, achieving the impressive
results.
The main advantage for digital photography is apparent.
With SLR camera capable of firing 6 to 9 frames per
second, there are no underwater strobes capable of
recycling to keep up with the camera firing speed.
Keeping unnecessary light out between the object and the
camera reduces the illumination of undesired back
scatter. In this department, a HMI light source is more
forgiving than an electronic flash. I also find that
light from HMI's seems to have the ability to "wrap
around" the subject, seemingly able to enhance depth and
soften shadow. Powerful units like the 1200w to 2400w
units provide greater true-color rendition over a wide
area, making them an ideal illumination source for
filming wrecks and wide seascapes. Here are some
examples of my work with HMI lights.
How to Use HMI lights
1. For DSLR start with ISO 400 and for Prosumer
camera, set to the highest possible.
2. Use S priority and set speed at 1/90 second
or higher
3. If your HMI unit offers power setting, use
the lower option.
4. Position HMI light in front of lens pointing
downward to subject at 45˚ angle.
5. Start with shooting macro at distant of 30cm,
using f16 aperture – bracket up or down for optimum
exposure
* to
diffuse hotspot, add a 3mm Perspex to the front of HMI/HID
light source.
The SOLARIS PRO HMI (BOX)
Highly recommended and
relatively affordable is the Keldan Solaris Pro. Using
metal halide high
intensity discharge globe, the light produces an
excellent light in daylight quality with its color
temperature of 5500 Kelvin. The rechargeable battery
pack is easily removable for recharging and the five
stage level indicator gives accurate information on
remaining illumination time.
