Hand Lens, or Loupe

- Every gardener should have one or two -

Summary: A good hand lens is indispensable to experienced gardeners for pest and disease identification. Most pest managers have a hand lens hung around their necks at all times. The best lenses fold into a closed position that protects the lens, are of moderate (10x) magnification, and made of glass.

Jack DeAngelis, PhD

OSU Ext. Entomologist (ret.)

Hand lens use

A hand lens is a small magnifying "glass" (sometimes made of plastic) that generally folds into a protective case (right). It is one of the most useful tools for a gardener, next to gloves. A good hand lens allows you to get a close-up view of potential pests and diseases as well as beneficial organisms. As you get better at identifying the various critters in your garden you'll come to appreciate your hand lens.

In use, hold your eye close to the glass and move your head and hand lens toward the sample until it comes into focus. With a little practice you'll quickly learn the best way to focus.

Hand lens (about 3" long). Tie on a shoe lace, or lanyard, and hang it around your neck so it's handy.

Parts of a hand lens

Lens elements -- All optical lenses consist of one or more elements. An element is an individually shaped piece of glass or plastic. Generally the more elements the better the image quality because each element is designed to reduce a specific type of distortion.

A lens designated as a "doublet" has two elements and will produce a better image than a "singlet" (one element) while a "triplet", with three elements, will produce the best image. For comparison a high quality camera lens may have 4-6 elements, plus those used in focusing and zooming.

Glass versus plastic -- Glass lenses hold up better than plastic lenses and can be more easily cleaned. Plastic lenses, however, are lighter and less expensive.

Lens diameter -- Large diameter (3/4") hand lenses are much easier to use, especially for novices. This can be a very important consideration if you are new to hand lenses. Large diameter lenses are more expensive to produce, especially in glass, so larger diameter hand lens will be more expensive.

Magnification -- A 10x power lens is a good general purpose magnification for small insects, mites and plant diseases. Higher magnification can be harder to use but 16x (see photo above) is handy if you have a little more experience.

You can find hand lenses at stores that sell geology or rock collecting supplies. Avoid lenses made for jewelers because these tend to be too high in power. Get a lens of 16x or less, 10x is better.

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Guide to Insect & Mite Identification

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