Introduction to Cleaning Binoculars

Disclaimer: This page describes a general procedure for dismantling and cleaning an OLD pair of binoculars, and is prepared to help people identify the parts of binoculars. Knowing what to expect inside the binoculars helps make the job easier and inspires confidence. Obviously it is assumed you are confident with small parts and tools, cleaning solvents and materials, and that you are prepared to accept the consequences of taking your binoculars to pieces. It is probable that your binoculars are no longer covered by any warranty/guarantee, but if it is then you might instead consider returning the binoculars to the manufacturer for professional cleaning. You would be well advised to think twice about dismantling/cleaning a new pair of binoculars - I am not an expert in the subject! Take care and you should be fine.

Cloudy Nights forum has a link to some companies that will service binoculars (including full internal repair/cleaning and collimation of prisms)

These Super Zenith High Quality Triple Tested 10x50 Wide Angle 7° FOV binoculars were given to me by my father who owned them for about 20 years, and yet another 30 years on they are one of my most treasured items. They have certainly stood the test of time.

Being a convenient size I usually take them on holiday with me for general casual use, and they have been used many many times for stargazing. Dad used them mostly for ornithology, and he likewise had many years enjoyment from them. Often I have looked at them and thought that really they could do with a good clean, and recently I have found them to be quite stiff to focus and adjust.

As you can see from the photo below they are a bit messy, so I figured it was high time they got some tender loving care.

Note: This page is about cleaning the mechanics of the binoculars to remove dirt, old grease, and maintain the binoculars so they operate freely and smoothly again. It is not about cleaning the optical glassware (prisms, lenses or eyepieces), which require the utmost care if they are to be cleaned. As a start I would highly recommend you read the two links found in the Useful Resources section at the bottom of this page, as these give some general hints and tips for Cleaning Binocular Eyepieces, and will make you aware of the importance of a delicate touch and avoidance of rubbing eyepiece lenses when dust and dirt may already be on them, as that is the surest way of creating fine scratches in the glass.

You can click most of the photos on this page to enlarge them, then hit your Back key when done.

Getting familiar with the Binos before taking them apart

The view below looks down on the focusing thumbwheel, and the ocular viewing angle pivot.

One thing to do before you attempt to dismantle binoculars is to make a very close and careful inspection, and either make mental note of the position of the parts (if you have a good memory), or better to write notes so as to help re-assembly once the cleaning has been completed.

Making these kind of notes helps confirm that you have done things correctly while re-assembling.

For example take note of;

  • The location of access screws to allow sections to be removed.
  • The location of washers, their sizes, shapes, diameters, types, any curvature, and which way round they are as you remove them.
  • The location of any tiny grub screws which fasten adjusting rings on eyepieces, and their position relative to the binocular body or eyepiece, so as to allow correct position to be re-established when put back together (this is particularly important for the di-opter adjustment position of the right-hand eyepiece.
  • The maximum and minimum focus adjustment end stop positions (in-out adjustment of the eyepieces relative to the body).

Often binoculars are constructed very cleverly, with concealed retaining screws. Never force something apart, as there is probably a clever, but simple method of undoing something that you have overlooked.

Preparing Your Work Area

To help with this, you should be organised and setup a clean working area with plenty of space, cover it with old newspaper because there will be considerable gunky old grease to be removed which tends to get on your hands, tools and work surface.

Lay down some plain white sheets of paper, or a couple of old saucers, pots or similar containers. This is where you will place the parts in an ordered fashion as you dismantle the binoculars, and white surfaces make it easier to see tiny parts such as grub screws. Position the sheets/containers near the back of your workbench so you are not leaning over them, to prevent accidentally brushing or tipping the parts onto the floor where they could easily be lost.

You will require:-

  • An assortment of small tools, pliers, screwdrivers ranging from wide flat-blade screwdriver, to a set of watchmakers fine-tipped flat-blade and cross-head screwdrivers for very small screws.
  • Tweezers to pick up and insert tiny grub screws
  • White spirits/turpentine to dissolve grease (do NOT use Acetone as this can dissolve some paint or plastic surfaces)
  • Isopropyl alcohol to clean off any grease residue
  • Washing up liquid / soapy water to fine clean any alcohol/grease residue
  • Distilled water to rinse off any soap residue (Optional, depends how well you wish to clean eyepiece lenses. Spring/mineral water is not good enough)
  • Old toothbrush to clean grease out of threaded sections
  • Kitchen roll - for rough cleaning of grease
  • Tissue paper for final-stage wiping of grease off using alcohol
  • Plenty of cotton buds (Q-Tips)
  • Lint-free soft microfibre cloth (for careful cleaning of optics)
  • Notepad and pen to write notes, or draw diagrams if you need to.
  • Lithium Grease (from local garage, or cycle shop) - I only needed a little, so I visited my local Ford car dealers service centre, and asked if they had any Lithium grease to spare. The service centre guy kindly squeezed some into a sealable polythene bag and gave to me for free when I explained what it was for.

During the cleaning process you must frequently change/refresh your cleaning materials. Expect to use about 20 or 30 cotton buds, and probably as many sheets of kitchen roll and pieces of tissue paper.

Dismantling the Binoculars

Most binoculars are constructed similarly, so the following instructions should help with your binoculars, but you may find some differences which you will have to make allowance for.

If your binoculars are particularly dirty, it may help to give the outside of them a first clean with a soft cloth moistened with soapy water. This will reduce the chances of getting dirt or dust inside the binoculars when you open them up.

On the top of the binoculars, remove the screw holding the eyepiece bush screw cover in place (the cover has the degrees of angle markings on it).

Once the cover is removed you can see the brass eyepiece bush screw holding the eyepieces in place. This screw threads into an aluminium thread, and I found it was a bit difficult to remove due to oxidization of the aluminium around the brass thread. Some careful gentle back-forth motion of the screw eased this up and allowed the screw to be removed.

Just beware as you dismantle that some items may well be a bit solid with age, and you need to be careful not to force things. If something seems really stuck, think about whether it is actually intended to come apart - Are you undoing the correct part to release it? Using incorrect force may damage something.

As you can see, once the brass screw was removed, the aluminium thread showed some powery residue where aluminium oxide had formed with age, so this was an area that I carefully cleaned with a cotton-bud and alcohol, and gave a very small amount of grease before it was re-assembled.

With the brass screw removed, this releases and allows the right hand eyepiece arm to be lifted and the eyepiece removed from the binoculars. Under the arm I found a brass washer which I removed, cleaned and put aside carefully, noting its position.

Initial Inspection and Cleaning

Next I was able to lift-off the left-hand eyepiece. Both ocular prisms can now be inspected for any dust or residue (see picture below). Hopefully you will find that the prisms are in pristine condition because they have been protected inside the binoculars. My intention was not to dismantle the optical path of the binoculars any further.

If there is any dust or dirt within, use some compressed air or a puffer bulb to try and blow it out.

If you don't have compressed air/puffer, you can try blowing, but do so carefully. Make sure your mouth isn't too wet with saliva, or you might end up blowing minute spots of spit onto the prism which will mark the glass. Certainly don't "trumpet" your lips as this will spray spit onto the glass. If in doubt, and strange as this might sound, practice blowing onto a house mirror first to get your blowing technique right without spitting! Your breath will have moisture in it but that should evaporate off the glass in a moment. The point here is to try and carefully blow off any dust. If there are any stubborn bits you can moisten a cotton bud with a tiny amount of alcohol, and gently attempt to lift off the particles (not brushing across - but lifting up).

If in doubt leave it alone!

Now that the interior is exposed, be very careful as you work to not let any grease, alcohol, dust, tissue fibres, etc. drop onto the prisms within each ocular optical section. I prefer cotton buds for cleaning the eyepiece tubes, not tissue, because tissues run the risk of shedding fibres.

Excess grease around the eyepiece tubes was causing a problem for my binoculars. Since it was 50 or so years old, and had become quite tacky it was preventing smooth focus adjustment. In fact it had become so tacky that if I listened when adjusting the focus I could actually hear a light crackling sound as the eyepieces went in and out of their tubes!

First I used cotton buds moistened with a small amount of white spirits (Turpentine) to clean off the grease from the inner wall of the eyepiece tube (you can see the grease in the photo below).

Do not put too much spirits onto the cotton bud or you are in danger of it splashing off onto the glass prism. To help avoid this it is best to work with the binos laid down flat on the work surface so that any spirit droplets will remain in the tubes.

Hold the cotton bud firmly and wipe and rotate it around the interior of one tube to get the majority of the old grease out. Repeat for the other tube using the opposite clean end of the cotton bud. Get a new cotton bud and repeat with some more spirits, using an in/out action on the inside of the tube walls. Repeat until the main bulk of the grease has been removed and dissolved.

Now use another new cotton bud this time moistened with isopropyl alcohol. Repeat the process until you are satisfied you've got rid of the sticky residue. At this point I then used a piece of tissue paper moistened with more of the alcohol to give a final wipe around the inside surface.

You will probably find that there is grease on the outer surface of the tubes as well. Just do more of the same cleaning process to remove it.

Seperating Into Two Halves

After removing the eyepieces and doing some initial cleaning in the tubes we can take apart the two halves of the binoculars.

On the underside remove the bottom pivot axis screw cover plate. This was simply a case of removing the centre cross-head screw.

This revealed the bottom pivot axis screw head, which required a wide flat-blade screwdriver to undo. Try to select a screwdriver blade wide enough that will fit snugly in the screw head. If the blade is too narrow you might dent the channel edges when trying to undo or retighten the screw.

Remove the screw, and note whether there is a washer underneath.

I found several very thin brass packing washers in between the sections of the pivot axis as I dismantled it. Make note as you pull everything apart of which sections they come from so that they can be re-assembled correctly.

Looking down into the hole revealed another brass screw head which holds the focus adjuster mechanism into the pivot axis body. Leave this alone for the time being, you will undo it once the focuser mechanism has been removed after dismantling the body.

Cleaning the Focuser Mechanism

With the main pivot axis screw removed it should now be possible to pull the pivot axis cylinder completely out of the binocular frames (quite a tight fit), allowing the pivot axis cylinder cover to come off (the black tube with eliptical shaped silver sticker which covers the metal frame giving it a nice finish), and the various brass packing washers to be removed from the focuser shaft. It may be necessary to rotate the frames about the cylinder as you pull to make it easier to withdraw the cylinder.

In this photo you can also see I have removed the recessed brass screw (shown in the above photo) which holds the focuser mechanism together.

The photo below shows the focuser mechanism completely taken apart. I discovered that the grease on this was not too sticky and didn't seem to be contributing to any stiffness. There was however some very fine aluminium powder filings from the years of use which had made the grease dirty.

So it made sense while it was apart to perform the same "degunking process", get it all cleaned up, and regrease with fresh Lithium grease. Since this was metal components (not optical glassware) that are now completely seperate from the ocular chambers, I was able to be far more liberal with the use of spirits and alcohol, and more thorough with the cleaning process.

I used the old toothbrush dipped in the white spirits to thoroughly clean the helical thread of the focuser, then used kitchen cloth with spirits, then tissue with alcohol, then washing the parts in hot soapy water, finally thoroughly drying the parts before re-applying the new grease using a cotton bud.

I generally kept one particular cotton-bud aside specifically for the purpose of applying grease, during the whole maintenance process.

You can be fairly liberal when putting the new grease onto the main focuser thread, as it contributes to the overall smoothness, and resistance of the focusers action. Don't forget to also apply a small amount of grease to the threads of the fastening screws before re-assembling the focuser unit.

Focuser Keying

Note in the photo below how the focuser mechanism has a slot, which keys with a raised pin in the ocular framework casting. This holds the outer focuser shaft stationary in relation to the binocular body, so that the rotation of the black knurled focuser knob causes the central shaft to move in or out of the focuser, thus moving the eyepieces to focus them.

Obviously you need to ensure the slot locates properly in the keying feature when re-assembling.

Cleaning the Left-Hand Eyepiece

The next picture shows the Left-hand eyepiece.

The eyepiece cup (at left) has been unscrewed from the metal frame (right), and this allows the eyepiece lens cylinder (centre) to be removed. Although this was not entirely necessary because the eyepiece lens itself was reasonably clean, I wanted to be thorough, and taking it apart like this allows easier degreasing of the frame and eyepiece cup with spirits, then secondary cleaning with alcohol, and washing with soapy water.

The lens itself can be given a gentler, more careful wipe clean of the body, and minimal cleaning of the lens glass itself. You don't want dissolved grease, alcohol or water egressing into any gaps around the lens, because this may cause residue, marking, or even worse, condensation on the inside of the lens unit. If that occurs you would have to unscrew the lens retaining ring (which requires a special tool to undo it), and carefully clean and thoroughly dry the lens glass.

After cleaning the parts I re-greased by using a cotton-bud to apply a very thin layer of grease to the outside of the eyepiece lens cylinder where it locates into the frame, and a light application of grease on the threaded portion of the frame where the eyepiece cup screws on, holding the unit together.

Cleaning the Right-Hand Eyepiece

Next to clean up is the Right-hand eyepiece (below), with its seperate focusing and Diopter Scale. As you can see below it has got sticky grease, and small hairs and dust.

This turned out to be the most awkward part to maintain.

Make careful note of the relative positions of the eyepiece cup and Diopter Scale to the Focuser, and also to the eyepiece frame itself. This will help when putting it back together again. In theory the top of the RH eyepiece cup should be level with the top of the LH eyepiece cup when the Diopter Scale is set on its centre-mark.

Taking it apart required undoing 3 tiny grub screws which hold the eyepiece cup onto the rotating threaded portion of the focuser. Dismantling is the easy part, but putting it back together again, and tightening the grub screws with the Diopter Scale positioned correctly on the centre-mark with the focuser adjusted to the same degree of focus as the Left-Hand eyepiece, was a bit more tricky. It took me a couple of attempts to re-assemble the RH eyepiece correctly!

The same notes made as before go for the care required while cleaning the RH eyepiece, except you have more de-greasing, cleaning and re-greasing around its focuser thread, at the same time trying not to get grease on the eyepiece lens.

Sidenote: In this photo you can see the black lens glass retaining ring which screws into the interior of the eyepiece tube. Look carefully and you can see a tiny square notch in the top of the far side of the ring (there is another opposite on the nearer side, but out of sight). These are the only means of getting a grip on the ring to unscrew it, and requires a special tool to do so. Hence my caution of being very careful while cleaning the lens, not to let dissolved grease/alcohol or water to get inside the lens unit, because removing the retaining ring might be difficult without a proper tool.

Here are the component parts of the RH Eyepiece after dismantling and cleaning them, ready for re-assembly.

Once again, use light re-greasing on the outer surfaces of the lens unit, and the fine screw threads, and a more liberal application on the focuser thread to promote a nice smooth action, but not too much to result in excess grease squeezing out when the focuser is operated.

Putting it all back together

After everything is cleaned to your satisfaction, its a fairly straightforward matter of re-assembling everything.

There are a couple of things to be careful of as you do so;

  • Lightly re-grease the screw threads.
  • Do them up tightly but be wary of overtightening and stripping the threads. If your binos are like mine - many years old - you should bear in mind some of the screws could be suffering metal fatigue, and could be more prone to breaking!
  • Make sure you get rid of any twists in the neck strap before re-assembling the two halves of the binoculars.
  • Ensure the packing washers are put back into their original locations.

Wash your hands.

Now give the body of the binos a final wipe off with alcohol moistened tissue or cloth, since it is highly likely the body parts have got grease on them during their handling while performing the work.

Fantastic - One nice clean pair of binoculars ready for another 50 years service!

New First Light - Was it worth it?

Using the binoculars after cleaning them is an absolute delight. The new grease has made the action of both main focusing and RH eyepiece focusing very light indeed.

Main focusing is very smooth, and easy to do with a light touch of my index or middle finger. A smooth action means that as you focus you can hold the binos very steady in your hands. Before cleaning, I would struggle to turn the focus wheel, which meant putting more effort into focusing, which in turn meant I was shaking the binos only slightly, but enough to make concentrating on focusing on the stars more difficult.

Likewise focusing the RH Eyepiece to match my left eyes focus is now incredibly easy. It is remarkably light, in fact almost too light, but I far prefer the absolute ease and rapid motion of adjusting the RH EP focus, to the constant fiddling I had to do. Originally I was forever getting a torch or going indoors to check whether I had the Diopter Scale on its centre-mark so I knew for certain what my starting point was, before attempting to focus it.

You see, the trouble was that with the old sticky grease lining the eyepiece tubes, it was causing each eyepiece (pivoting slightly on their yoke arms about the central focuser mount point), to move in or out by different amounts while focusing! No wonder I was always finding it so frustrating to focus properly.

Useful Resources