When I was a new diver, I was out for the big stuff. But
after seeing hundreds of barracuda and lobsters, I appreciated
more diverse pleasures in the reef environment. That’s
where my magnifying glass comes in. The tiny shrimp lurking
in the lettuce coral, the clinging crab in the anemone
and the pipefish in the sand flats are easier to identify and a
lot more spectacular with a good glass. I also get a lot more
detail on other denizens, including the corals.
If you want to go small, you need a glass lens, not plastic.
That’s because the index of refraction of water is about
1.33. Plastic lenses have about the same index as water, so
they become useless underwater. Optical glass has an index
of about 1.52, so it works, though the magnification underwater
will be a bit less than above.
Index of refraction? That’s a measure of how much a
substance slows the speed of light, and thus bends (refracts)
it. Water’s index of 1.33 also explains why objects appear a
third larger underwater -- and why your buddy swears that a
three-foot grouper was a four-footer.
Magnifying lenses in your mask (bifocals) are not very
useful for viewing underwater subjects except gauges. This
goes for the plastic stick-on bifocals as well as the Mares
ESA mask, which has separate lens frames in which you can
put magnifiers.
Instead, you need a good hand-held glass. My favorite is
from Edmund Scientific (www.scientificsonline.com). Look
for the Round Magnifier with 10X Spot Lens. The four-inch
lens (you don’t want a small one that you need to hold too
close to the subject) is available there for $11.95, plus $7.50
for shipping. It fits in a BC pocket and has a hole in the
handle for a lanyard. Happy hunting.
- - M.A.