Dismantling Binoculars

In general, you should not attempt to dismantle your binocular. Unless you know precisely what you are doing, you run the risk of causing more damage than you are attempting to remedy! You would also immediately void any warranty. The single exception for the layperson is when a faulty binocular has been pronounced, by someone who is qualified to do so, unworthy of repair, either due to the extent of the damage or because the cost of repair would exceed the value of the binoculars. In these instances, there is a valuable experience to be gained.

The faults that can be relatively easily repaired are dust or flora in the binocular, prisms that have been displaced by impact, and grit or failed lubrication in moving parts. The simplest binoculars to dismantle are Porro prism varieties. If you attempt this, which you do entirely at your own risk, first prepare your work surface. I prefer to cover the work surface with plain white paper—sheets of acid-free tissue are ideal. I have a few plastic containers for components, and I ensure that any tools I use are clean. I use disposable powder-free latex gloves to handle optical components.

If the binocular has a Zeiss-type body, the objective tubes can be simply unscrewed from the binocular body (Figure 5.3), giving access to the inside surface of the objective lenses. The lower prism cover plates can then be removed, giving access to the lower prisms. These are often held in place by clips. In the Bausch & Lomb type of body, the objective cell must be removed from the tube. First remove the front protective ring—this usually simply unscrews. In this type of binocular housing, you do not gain access to the prisms from this end.

The objective lenses are held into their cells (which, in Zeiss types may be integral with the objective tubes) by a locking ring and usually a seal ring. The locking ring should be removed using a peg-spanner,but this can be done with extreme care with a small screwdriver with a blade that fits into the recess on the ring. The danger of scratching the lens is very great, and you should not attempt this unless you are willing to accept this risk. Before removing the locking ring, mark the eccentric rings with a soft pencil so they can be returned in the same orientation. If you remove the lens elements, mark the edges with a soft pencil with an arrow pointing to the front surface. Wrap them in acid-free tissue and put them safely in a container.

The dismantling of the eyepiece end and begins with the removal of the cover at the bottom of the hinge. If there is a tripod bush in the hinge, you will also need to remove this; it is slotted for a screwdriver for this purpose (Figure 5.4). This reveals a hole in the hinge, deep within which is the screw that holds the focus shaft in place. Use a flashlight to ascertain what type of head the screw has, and insert a screwdriver into this hole to undo the screw. A small amount of Blu-tac® or other similar adhesive putty on the end of the screwdriver aids the removal (and replacement) of this screw (Figure 5.5). When the screw is removed, use the focus wheel to drive out the eyepieces and bridge (Figure 5.6). The focus shaft should be

Figure 5.3. Objective barrel unscrewed. The prisms are visible under the cover plate.

Figure 5.3. Objective barrel unscrewed. The prisms are visible under the cover plate.

Figure 5.4. Tripod bush removed. This gives access to the screw that secures the focus shaft.
Figure 5.5. Adhesive putty holds the screw to the screwdriver.

Figure 5.6. The bridge and eyepieces are lifted clear.

Figure 5.6. The bridge and eyepieces are lifted clear.

greasy; do not allow this grease to get on to optical surfaces or parts that may transfer it to the optical surfaces.

Once the eyepieces and bridge assembly are removed, the eyepiece guide tubes must be unscrewed (Figure 5.7). Then remove the screws that secure the top cover plate and remove the cover plate (Figure 5.8). Ensure that you store screws in such

Figure 5.7. The eyepiece guide tubes are removed.

Figure 5.7. The eyepiece guide tubes are removed.

Figure 5.8. Undo the cover-plate screws.

a way that you know which screw goes where. In Zeiss-type bodies, the upper prism will be held in place by a clamp. This may be screwed down at one end (Figure 5.9) or, in cheaper binoculars, have both ends clipped under recesses. The prism may also be protected by a shaped piece of metal or card-type composite.

In Bausch & Lomb type bodies, the prisms normally remove as a cluster (Figures 5.10 and 5.11). The screws that secure it in place are the ones immediately adjacent to the slotted-head grub screws (set screws) that are used for collimation. The prisms are secured to the cluster plate with clamps that are screwed to the plate.

The eyepiece lenses are retained with a lock ring. If you decide to dismantle the eyepieces to clean the components, be sure to mark the edges of the various lenses and spaces so that you know their order of reassembly and the direction they should face. Also be aware that there may be as many as six separate lens elements.

The only time it is necessary to dismantle the hinge is when the tension needs to be adjusted. Remove the cap with the IPD scale on it and you will see a slotted brass tension screw with a locking grub screw (set screw) in it. If you need to adjust the tension, loosen the locking screw and adjust the tension screw with a screwdriver. The correct tension is achieved when it is just sufficient to prevent one side of the binocular from sagging under the effect of gravity when the binocular is held by the other side.

When you reassemble the binocular, it may be necessary to lubricate some of the mechanical parts. Use a good quality lithium grease for this. Use the minimum amount necessary and ensure that none is able to escape to the outside, where it will inevitably be transferred to the external optics. If screw threads are slightly stiff and tend to bind, you can lubricate them by running a soft graphite (lead) pencil along the thread. (Incidentally, soft pencils are also useful for lubricating stuck zippers and stiff lock mechanisms.)

Figure 5.11. Prism cluster removed.

Figure 5.11. Prism cluster removed.

If miscollimated binoculars are still under warranty, return them to the supplier. The supplier should have access to a binocular repair shop that has proper colli-mating equipment. Proper collimation is a skilled task and miscollimation can be expensive to remedy on binoculars that are out of warranty. It can cost more than the binoculars cost in the first place and is therefore usually not worth having done on budget-priced binoculars. If your binoculars are out of warranty and you feel confident of trying to do it yourself, here is how. The methods described in this book will result in conditional alignment (i.e., the optical tubes will only be aligned at the interpupillary distance at which you perform the alignment). Binoculars can be collimated by either eccentric rings on the objective lenses or by tilting the prisms with grub screws (set screws). There is no substitute for experience in col-limation. If you can, practice on an old misaligned binocular where you will not be upset if you are unable to achieve the collimation you want.

Always collimate binoculars outdoors, or indoors by looking through an open window. Window glass is usually nonuniform and can differentially affect what you see through each side of the binocular. Collimate by looking at an object at least 100 m (110 yd) away, but preferably further.

If the binoculars were once properly collimated and have suddenly lost colli-mation, this is most likely due to being dropped or bumped, causing a prism to shift. It is therefore worth examining the prisms to see if there is any obvious shift. Often, if a single prism has shifted, a symptom will be that the image in the affected tube will have acquired a "lean" (i.e., it will be tilted slightly to one side or the other). Prisms are held either to the body of the binocular (Zeiss or European style) or in prism housings (Bausch & Lomb or American style) by straps. A sharp jolt can move the prism, and if this has happened, it can usually be replaced. In budget binoculars there is usually no possible adjustment of the prism once it is located and secured into its recess in the binocular body (see Figure 5.9).

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