Establish a clean, uncluttered, well-lit working environment. The kitchen table is usually a good choice. You'll also need a strong light, such as a flashlight, that you can direct at a grazing angle against the lens surface to reveal grit particles on the lens. If you are cleaning a large lens, such as a refractor objective, that you have removed from the scope, wear thin cotton gloves to avoid getting fingerprints on the glass.

Never clean a lens at the observing site if you can possibly avoid doing so. If you must clean a lens in the field, work inside your vehicle or another sheltered location where you can avoid the dust often present in outside air. Use a strong white light. It's impossible to clean a lens safely under red light because you can't see the grit particles that will scratch your lens.

Use an ear syringe or similar device to blow off any dust visible on the surface of the lens. Don't use your mouth, or you will probably spray saliva on the lens. (In an emergency, we have blown through an ordinary drinking straw to remove dust from an eyepiece.) Don't use canned air, either, because it may spray propellant onto the lens.

Examine the lens carefully under a strong light to make sure no dust or grit remains on the surface. You can remove a persistent particle by slightly moistening a tissue or cotton swab with Windex or a similar cleaning solution and blotting (not rubbing) the surface of the lens to pick up the particle. If necessary, use the blower again to remove any remaining dust.

Although you can buy lint-free lens cleaning tissue, we prefer to use ordinary facial tissue or toilet paper. If you do the same, make sure it's unscented and not treated with lotions or other adulterants. Toilet paper is particularly safe because you can simply unroll the outer layer or two to get a piece certain to be free of grit. Some people prefer to use cotton swabs or cotton balls. If you do that, make sure they're pure cotton (often described as surgical cotton) rather than an artificial fiber. Cotton balls and swabs sold for medical use are usually pure, grit-free, sterile cotton. Those sold for fingernail polish removal are often made from artificial fibers and may contain grit.

Moisten a tissue or cotton swab with cleaning fluid. You want it damp, but not dripping wet. Begin at the center of the lens and wipe outward very gently, using a circular motion, as shown in Figure 4-17. If you've used too much cleaning fluid, it will spread over the lens surface. You want the swab or tissue to be just wet enough that you can watch a bead of cleaning fluid follow the movement of the swab or tissue. If you stop moving the swab or tissue, it should immediately reabsorb the bead of cleaning fluid. If you've used too much cleaning fluid, or if you move the swab or tissue too quickly, the bead breaks away from the swab or tissue and will dry on the lens, leaving spots.

Figure 4-17. Cleaning a binocular objective with a cotton swab

Replace the tissue or cotton swab frequently as you clean the lens. You may be able to clean an eyepiece or other small lens with one tissue or cotton swab. For larger lenses or smaller lenses that are badly smudged, using one tissue or swab too long merely spreads the gunk rather than picking it up.

The edge of the lens is the hardest part to get clean. As you approach the edge, replace your tissue or swab with a tissue folded into a sharp corner and moistened slightly with cleaning fluid. (Make sure not to touch the working area of the tissue with your finger to avoid contaminating it with skin oils.)

When you complete this procedure, the lens should appear clean when examined with a strong light at a grazing angle. If any lint fibers from the tissues or swabs remain on the lens, use your blower to remove them.