Basics of Underwater Stereo Photography
© PSA Journal written by John Roll
Back in the summer of 1995, I was visiting the RBT factory where the
cameras are made. Eckhart Oehmichen showed me different prototypes - and
they were all very interesting. I was shown an underwater housing for the S1
model and I thought that it was very nice, but not something that I wanted.
However, for the next six months I thought about this housing. I finally
contacted RBT and said I must have one! The camera and housing cleared
customs the night before my wife and I left for Grand Cayman Island, where I
was to do my open water certification dives to complete my dive training.
Later in the week, I was certified in the afternoon, and that night I was
diving with a stereo camera!
Over the past few years, I have shown my underwater stereo slide
presentation "3D in the Sea." Afterwards, there are always questions about
this technique of photography. In this article I would like to explain the
differences between 2D and 3D photography, above and below water.
As soon as you go underwater, things look different. Not only do you start
to lose the available light, but the color spectrum of the light also begins
to change. The water acts as a giant light filter. The red end of the color
spectrum is lost first, and then color is lost progressing across the
rainbow from red toward the blue end. That is why many underwater
photographs have a distinct blue hue if they are taken with only available
light. This can be corrected by using a flash; however, the flash has a
limited range underwater. People also tend to think of water as being
crystal clear. Not so! The truth of the matter is that a diver is fortunate
to have 20 to 30 meters of visibility underwater. There is a lot of
particulate matter in the water that can make photography difficult. So, not
only do you have to deal with loss of light and color (best corrected with a
flash), one has to also worry about visibility. These are factors that favor
having your underwater subjects closer to you, rather than further away.
I mentioned that water acts like a giant light filter, but it also acts like
a lens as well. The index of refraction of water is 1.33. What does this
mean to the average person? When a diver is wearing a scuba mask, or your
camera is behind a flat piece of glass in a housing, objects that look like
they are 1 meter away are actually 1.33 meters away. Objects are further
away than you think (See the diagram on p.23). Fortunately, if all object
looks like it is I meter away underwater (when in reality it is 1.33
meters), if I set the focus of the camera to one meter, the object will be
in focus. I just have to point my flashes to cover the object at 1.33
meters!
Not only do you need photographic skills to do underwater photography,
you must have good diving skills. Safety is the most important factor.
Buoyancy control is also extremely important. This skill can simplify your
underwater photography immensely. You can not really compose a good picture
if you have a tendency to sink or rise to the surface. Being able to raise
or lower yourself in the water by half a meter with minimal effort will
increase your ability to get the shot.
The use of a flash underwater can result in the illumination of particulate
matter between the lens and the subject. This is a bigger problem for 3D
underwater photography when compared to 2D underwater photography. The
solution to this common problem is to have the flash (or flashes) on an
extension away from the camera. This way you will illuminate the subject and
not the particulate matter between the lens and the subject you are
photographing (Refer to the diagram).
What about the other differences between 2D and 31) underwater photography?
Well, the most obvious difference is how much better 3D photography is, but
that goes without saying! There is a considerable difference in the camera
equipment and housings. Regular 2D underwater equipment is readily
available, but that is not the case with underwater 3D photography. You
would need to plan well in advance to purchase a camera and have a stereo
housing manufactured! I use an RBT camera (with a 45mm stereo base) and a
housing made by UK Germany. Since there is a limited amount of equipment
available, the lens selection is also limited. With 2D underwater equipment
you have the choice of wide angle (15mm) to longer focal lengths (such as 50
to 100mm). The advantage to the wide angle 2D lenses is that you can get
very close to your subject to fill the frame, and have very little water
with particles between your camera and the subject. The most common stereo
camera focal length available is 35mm. With this focal length and usually a
reduced stereo base, there is a limit to how close you can get to your
subject.
Of course depth of field is more important for stereo photography. If you
increase your depth of field, you will reduce the ambient light available at
a given shutter speed. This will make you more dependent on the light from
your flash. I usually use two big flashes to give me even illumination and
as much light as possible. This way I can maximize the depth of field. Since
I have reduced the exposure due to ambient light, the background may look
like it was taken during the night. Sometimes it is difficult to distinguish
between photographs taken during the day and those taken on a night dive.
There are many differences between 3D "land-based" photography and 3D
underwater photography. Another factor to consider is that subjects are
usually closer underwater so a reduced stereo base is desirable.
So there you have it! As you can see, there are many factors to consider
when doing underwater stereo photography, if you enjoy diving and are
willing to spend an excessive amount of time and energy, then you might want
to consider underwater 3D photography!
© PSA Journal written by John Roll