The front surfaces of high quality lenses are covered with an anti-reflection coating that is easily damaged.

Never touch optical glass. The acid on your skin can etch the coating, which is nearly as bad as scratching the lens.

Avoid wiping the lens with anything other than lens tissue designed for the purpose. Even high quality facial tissues contain bits of wood that can scratch optical surfaces. Many also contain lotions that will degrade the image if left on the lens.

The usual result of an etched, scratched, or lotion smeared lens is a sort of halo around the bright areas of the image. Not good unless you only photograph saints.

When you have to clean a lens:

1. Spray with compressed air or brush with an optical brush. If it looks clean, stop here.

2. If you can still see fingerprints, dust or a smeary film, wad a piece of lens tissue, wet with a drop or two of lens cleaner, and wipe the lens gently in a circular motion.

3. If you use too much cleaner, or any time the lens is wet, wipe with a clean wad of lens tissue.

Only use brushes, tissue and cleaner you buy at a camera store. Eyeglasses are not coated so even the cleaning materials available at opticians may not be suitable for camera lenses. Non-optical cleaners may contain solvents that dissolve the cement used to hold lens elements in place.