Know your gear

What to know when selling binoculars

A pair of binoculars fulfils the function of a telescope in magnifying a distant object to make it visible, and essentially comprises two telescopes that are mounted side by side – one for each eye – and aligned to point in the same direction – their advantage over a single telescope, or ‘monocular’, being that they are used with both eyes, which gives a more natural, three dimensional image.

Binoculars come in two main types — the small compact form in which the ‘objective’ (which gathers the light) and the ‘eyepiece’ (which one looks through) are in a straight line, and the larger more bulky form, in which the objectives are offset from the eyepieces (with more complex internal optics).

The key to understanding binoculars is to understand the figures with which they are described: all binoculars come with a specification, such as 8x40 or 10x50 and these two figures give an indication of the binoculars’ performance — the first figure referring to the magnification, or the number of times that the image is magnified, and the second to the diameter of the objective lens in millimetres, which is indicative of the light gathering power of the binoculars.

In general, the larger these two numbers are, then the more useful the binoculars will be, but the penalty is that the binoculars also come with increasing size and weight, not to mention cost.

In practice however, there are limits to these specifications: a magnification of 10 is the largest that is practical for hand holding and that requires a very steady hand! Binoculars with a larger magnification generally require a tripod.

An 8 is probably the most useful magnification for general use, particularly for a family in which the bins will be used by the various family members of different ages.

Similarly, for general use an objective size of 50 is the maximum that should be recommended and again binoculars larger than that normally require a tripod because of their increased weight.

Typically compact binoculars have objectives up to about 25 mm, while standard binoculars have larger objectives.

In selecting binoculars a number of questions need to be asked: What will they be used for? Is a compact binocular preferred for travelling? If one is out in the field all day will a large pair of binoculars be comfortable to have around one’s neck?

Most importantly, the buyer should be encouraged to try out the binoculars, even if just to view the opposite side of the street — surprisingly, binoculars of apparently similar quality from different manufacturers can vary considerably, for example in terms of image brightness.

Are the binoculars comfortable to hold in the hand and easy to use? Often, like so many other items, the final choice may come down to one of personal preference — bearing in mind that quality of binoculars is broadly related to their price and in general the more expensive the binoculars the better the quality of their optics and build. Indeed, cheap, no name brand binoculars should be avoided at all costs as their quality is likely to be so poor that they end up unused on the shelf and their owner disappointed.

Also to be avoided are binoculars with features like zoom or image stabilisation, as these are normally heavier and more expensive, and do not perform as well as the binoculars of the same specifications without these features.

Any reasonable pair of binoculars will have separately focusing eyepieces, in order to accommodate the normal minor differences in optical quality between one’s two eyes. Assuming the right eyepiece is separately adjustable, the procedure is to focus the left eyepiece with the main central focusing wheel, and then to separately focus the right eyepiece. With the relative focus for both eyes fixed, thereafter only minor adjustments will be required with the central wheel to focus for distance.

Looking after binoculars

Binoculars are a precision optical device and they require care in handling. They should not be knocked or dropped as, apart from damaging the casing, the optics can go out of alignment or come loose in extreme cases. In that case they should be taken to a specialist for repair and the owner should not attempt to repair them him- or herself. The optics comprise several components, which could easily be mislaid or damaged, and their correct alignment requires sophisticated testing.

Binoculars also should not be allowed to get wet, although the odd drop of moisture is unlikely to harm them. If they do get wet, they should be dried off carefully. Sea water or spray is particularly damaging to binoculars, as is sand, and particular care needs to be taken at the beach or near the sea.

Care should also be taken with the optics and the lenses should preferably not be touched to avoid fingerprints. Better quality binoculars have lenses with optical coatings, which improve the image quality, and these may be easily scratched. The lenses should be cleaned in the same way as a camera lens, starting with a blower brush to remove any grit or other matter which might scratch the lens coating. Then the lens may be cleaned by rubbing gently with lens tissue or a soft, old well-washed handkerchief. Avoid tissues, which contain fibres that will scratch the lens coating.

When not in use, binoculars should not be allowed to stand in the sun, and they should be stored in a cool dry place. In occasional cases, such as particularly humid or damp conditions, condensation and/or mildew may occur inside the binoculars and then they should be taken to a professional for cleaning.

That said, hopefully the binocular will not spend too much time in storage, as a pair sitting in a cupboard is money wasted. Binoculars are designed to be used, even if they do get a little damaged along the way — and if the owner is happy with his choice, the binoculars will be used, opening up new, otherwise inaccessible vistas.