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The Private, Exclusive Guide for Serious Divers Since 1975
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January 2006 Vol. 21, No. 1   RSS Feed for Undercurrent Issues
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Delight in the Details

from the January, 2006 issue of Undercurrent   Subscribe Now

On my last trip to Cozumel, besides nurse sharks and turtles, I didnít see big critters. But I saw an eye-popping painted elysia sea slug looking as fine as the one pictured in Paul Humannís Reef Creatures.

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.

Thatís 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 ID and a lot more spectacular with a good glass. I also get a lot more detail on other denizens, including the corals.

Delight in the DetailsIf you want to go small, you need a glass lens, not plastic. Thatís 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? Thatís a measure of how much a substance slows the speed of light, and thus bends (refracts) it. Waterís index of 1.33 also explains why objects appear 1/3 larger underwater, and why your buddy swears that a 3-foot grouper was a 4-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. Iíve tried several and my favorite is Edmund Scientific ( Look for the Round Magnifier With 10X Spot Lens. The 4-inch lens (you donít want a small one that you need to hold too close to the subject) is available there for $11.95, plus $6.40 for shipping. It fits in a BC pocket and has a hole in the handle for a lanyard. Happy hunting.

Ė M.A.

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