How to clean binoculars and telescopes

If looked after well binoculars and telescopes can keep working for many decades, but inappropriate cleaning can cause potentially expensive damage. We have seen many badly scratched lenses and seized eyecups and focusing wheels that could have been avoided by following a few simple rules that will keep your kit in tip top condition.

Keep it clean.

Sand, fingerprints and dust. Time for a clean.

This may sound obvious, but if you want to avoid the risk of damage then not cleaning too frequently is best. Optics that are used in the field will get dirty eventually but using rainguards and lens caps will help keep the muck out for longer.

Try not to clean when out in the field.

This is usually when damage is done. It is not always convenient to carry a full cleaning kit in the field and the temptation to quickly remove a speck or smear with a cloth or the hem of your shirt/scarf/skirt/pants can be great, but resist!

Clean at room temperature.

If you try to clean when the lenses are too cold it is very hard to successfully remove any greasy marks and you tend to just spread the muck around.


All you need to keep clean.

Use the right tools for the job.

What you need is:

An air blower

A soft brush

A clean lens cloth

Lens cleaning fluid

Step 1:

Don't touch the lenses yet! The first thing to do is remove any loose dust, sand or grit without risking getting it embedded in the lens cloth or scratching the lens coatings. The best way to do this is using a rubber bulb type air blower with the lens facing downwards to allow any grit to fall out. After you have done this use a soft brush to flick out any bits that the blower didn't shift.

Step 2:

And breathe... A quick huff or two on the lens for a coating of moisture works a treat, then using a lens cloth to wipe round. Don't push too hard with the cloth and fold it so that you have two or three layers under your finger. If there is a single spot or fingerprint on the lens then try to remove this without spreading it all over the lens.

Step 3:

Still not clean? If there is still smearing on the lens then a little cleaning fluid should sort it out, but don't spray it on to the lens because it will be very difficult to remove it all and with some older bin it can seep inside. Spray onto the lens cloth and carefully apply it to the greasy area only, then another breath on the lens and wipe with a bit of cloth without cleaning fluid on.

Salt.

Salt under the microscope. The hard, sharp-edged crystals
can easily scratch lens coatings

When you are out by the coast in rough conditions everything will get covered in spray and when this dries hard crystals form which can scratch the lens coatings. To avoid this the crystals must be dissolved before cleaning. Start the cleaning with step 1 then proceed as follows. If there is only a light covering of spray then the condensation from warm breath is often enough but if the lenses are well encrusted then it becomes a little more tricky. With fully waterproofed optics you can use a shallow bowl of warm water to just dip the lens surface into for long enough to let the crystals dissolve. With non-waterproofed optics the risk of getting moisture inside is too great for this to be recommended, so breathing on the lenses when they are cooler will have to suffice and is often enough. After this then follow step 2 again.

Sand.

It gets everywhere. This is the worst enemy don't miss out on seeing something because you are trying to keep your bing it around it will find its way into eye cups, focusing wheels and hinges. While there is not a lot you can do about this keeping your rainguard on as much as possible will help and if you have twist-up style eye cups turn them down to keep sand out of the mechanism. When you get home follow step 1 to remove as much as possible without touching the lenses.

DEET.

Many insect repellents contain the chemical N,N-Diethyl-meta-toluamide (C₁₂H₁₇NO) commonly known as DEET. This is a volatile chemical that is very good at keeping the mozzies away but also attacks rubber armouring and some plastics on binoculars and scopes. While there are some places where the insects are so numerous and determined that DEET is the only option, it is best kept away for you optics or the rubber may begin to peel, bubble and crack with repeated contact.

Birdwatching optics are designed to be used outdoors and sometimes they will get dirty, so don't miss out on seeing something because you are trying to keep your binoculars clean, but a little care goes a long way. Some hardened twitchers regard filthy kit as a way of showing you are a serious birder but this is no excuse for mistreating your gear and there is a difference between well used and abused. If you look after your optics they can last a lifetime.

Cley Spy