5 tips for cleaning binocular & telescope lenses

There's nothing like a close-up of lens dirt and dust to spoil a sky watching outing. Here’s a bit of friendly advice to keep binocular and telescope lenses clean.

• Try blowing gently on each lens, without spitting, to remove loose debris and dust.
• Or use a lens-cleaning pen, which has a soft natural brush at one end and a cleaning tip at the other, to get into the crevices. Most camera shops carry lens pens, lens tissue and cleaning fluid.
• Brush off the lens lightly with a sheet of lens tissue.
• With a clean sheet of lens tissue, sprayed lightly with lens-cleaning fluid, wipe the lens with a circular motion. Gentleness is the key here, since rubbing too hard can remove the protective coating.
• With a third sheet of lens tissue, remove the remaining fluid.
• Repeat with the other lens.
• Never use your shirt tail or facial tissue for this job because their fibres could scratch the coating.
• Also resist the temptation to use a commercial glass cleaner on your lenses. The ammonia in most glass-cleaning products will eat away the coating.

• Dampen a soft cloth with water and wipe.
• Keep rubber eyecups and focus knobs lubricated with a vinyl or rubber preservative.

• Less is always more. Telescope optics should be cleaned no more than twice a year because their reflective coatings are easily damaged.
• Carefully remove the mirror from the tube, then use a camel hair brush — sold at most camera shops — to remove surface dust and dirt.
• Dampen a sheet of lens tissue with lens cleaning fluid (or make your own cleaner using 3 parts isopropyl (surgical) alcohol to 2 parts distilled water).
• Wipe the mirror, eyepiece and lenses from the centre to the outer edge, using minimal pressure. Telescope optics are even more delicate than binocular lenses and don't take kindly to being rubbed in circles.
• Should the optics collect dew outside, don't wipe them dry. Instead, let them air-dry, then clean with distilled water and lens tissue. (Distilled water leaves no spots.)

• Always use the dust caps.
• Keep your telescope inside when not in use to prevent rusting. Most telescopes have an aluminium coating that can last for up to 10 years if it's kept spick-and-span.
• Before you store your telescope, wipe the outside dry with a soft cleaning cloth.

Whatever you do, don't be tempted to use saliva to polish your camera or binocular lenses, or rub them dry with your shirt tail. Both actions could irreparably damage the delicate lenses.