When to clean a refractor lens? Even a large amount of dust on a refractor lens will probably not have any visible effect on the image. That’s because the dust is at the pupil of the optical system and isn’t in focus. Therefore it is best to leave the dust on until it affects performance. Exceptions are tree pollen, tree resin, or insect droppings, or white spider droppings (usually found in observatories!), which can become hardened over time, and difficult to remove. These substances are best removed using commercial optical fluids designed for multi-coated lenses.

What lens cleaning fluids? Usually lens cleaning fluids contain isopropyl alcohol and a little detergent with water, which dissolves or loosens foreign substances. You can also use pure IPA.

What lens cleaning wipes? Always use professional lens tissue. Do not use household tissue, or synthetic cloths, or any other materials which are not specifically designed to clean lenses. We do not recommend using the “fluffy” micro fibre cloths to clean a refractor lens – they tend to trap dust and scratch surfaces. Professional, disposable, lens tissue is the safest method.

How do I clean a refractor lens? If using optical fluid in a spray bottle, do not spray directly onto the lens. Instead, spray the lens wipe. The best way is to use a bulb style dust blower, which is hand operated. Never use compressed air can or aerosol blowers, because they can damage the lens. When the dust is largely removed, you can give the lens deeper clean by using professional lens wipes which are dampened slightly with optical cleaning fluid. Gently roll and pull the lens wipes so they pick up the dust without dragging the dust over the lens surface excessively, and always wipe from centre to edge and vice-versa. Never wipe the lens in a circular motion.

If there is dust on the inner lens, follow these instructions to clean it.