Two main kinds of magnifying glass are useful to backyard naturalists. The best for general-purpose naturalizing is the hand lens, sometimes referred to as the jewelers' loupe, shown at the right. Hand lenses differ from the second kind of magnifying glass, the lollipop type consisting of a large lens mounted on a narrow handle, in four main ways:
Hand lenses are much smaller than the lollipop type, with lenses only about the size of a quarter
Instead of just one lens, hand lenses have two, with one lens mounted above the other
The hand lens's lenses swivel as a single unit into the handle for storage
Hand lenses provide much more magnification than the lollipop type
Average naturalists, to whom an acorn is as interesting as a sea gull, probably use hand lenses more than binoculars. Hand lenses are just the thing for looking at insects, for instance, when we must examine mouthparts, tarsi and wing venation, such as that at the left (a Cicada wing plucked from a spider web... ) during the identification process. With hand lenses we can see the wonderful diversity of egg types that bugs deposit beneath squash leaves in our gardens, and we can discover nematodes in the nodules of infested roots.
You'll find that many of a blossom's most important features can be seen only with the help of considerable magnification. For example, with a hand lens you can see how many "cells" or "carpels" comprise a flower's ovary, even if the ovary itself is so tiny that it's hardly visible. You can also see whether hairs on a leaf's undersurface are sharp-pointed or blunt, or possess glands. Needless to say, you're lost without a hand lens when studying mosses, lichens, and ferns.
Even field geologists use hand lenses. To identify rocks it's important to know which minerals are present, and often a mineral's identity is revealed by the shapes of minuscule crystals embedded in it. Calcite crystals are rhombohedral in form, while typical quartz crystals are hexagonal.
But, to tell the truth, maybe the most glorious thing to do with a hand lens is just to wander around looking at whatever is at hand. At the left you see what I saw the other day when I absentmindedly picked up a Black Oak leaf, held it up to the sun, and gazed at its veins through my hand lens. I was dazzled!
Here are three important rules for using hand lenses:
With regard to the last point, to show yourself the power in thinking small, on a nice day when you're lying in the grass, just roll over on your stomach and look beneath the grassblades. Put your nose right up to the soil and look at the earthworm castings, the wandering ants and ping-ponging springtails. Look at all the colors and designs of things the big world doesn't have. And use that hand lens to see those things even better!
Hand lenses are sold in a variety of places. Jewelry shops sometimes display them, but usually at prices much higher than you need to pay. Camera shops often have one or two displayed among the dozens of lenses inside their display cases, and this is probably the best bet for buying good lenses at reasonable prices -- probably around $10.
However, before buying in either of those places, you might check out the mall's toy shop. Sometimes pretty good lenses can be purchased as part of a detective kit. That way you can get a badge and false moustache, to boot!
A good magnification power is ten (10 X). Weaker lenses won't show some of the details we need to see but stronger ones will have such shallow depths of field that most of what is looked at will be out of focus.
Here are two suggestions to keep in mind:
Less powerful lollipop-type magnifying glasses display larger areas than hand lenses and thus are useful for looking at spiders and other small critters you don't want to get too close to. Or maybe you're watching a large number of ants devour a caterpillar and you want to magnify the whole field of carnage. So, there are uses for the reading kind of magnifying glass, but if you have to choose having just one, the little hand lens is much better.