Purchasing binoculars

1: Do you wear glasses? Pay attention to the eye relief!

If you are planning on purchasing binoculars and you wear glasses, then it is important to pay careful attention to eye relief. Eye relief is the optimal distance between your eye and the optical lens and this may vary from model to model. If you do wear glasses, you should ideally choose binoculars with an eye relief of at least 15mm otherwise you will not be able to see clearly through the binoculars when wearing your glasses.

2: Size of the binoculars

The size of the binoculars is of great importance. A small, compact pair of binoculars is naturally very handy as you can easily carry them around in your inside pocket but a large pair generally produces a brighter, clearer and more stable image. The image is clearer and brighter because a large objective lens gathers more light and it is more stable because large binoculars are able to reduce tremors and vibrations more effectively.
The model of the binoculars usually includes the magnification and objective lens diameter measured in millimetres. For instance, 8x42 means that the binoculars have a magnification factor of 8x and that the objective lenses have a diameter of 42mm. In fact, 42mm is a standard size as it is a good balance between the image quality and the dimensions.
Naturally, the objective lens diameter is not the only measurement that is important in binoculars. Porro prism binoculars are larger than roof prism binoculars (the difference between these two types will be discussed later) and the length of the binoculars can vary considerably.

3 Magnification of the binoculars

The magnification of binoculars determines how close the image can be brought to the viewer. The bigger, the better does not apply here! Vibrations and tremors are also magnified, for instance, and if an object is magnified more than 8 times, your brain is less well-equipped to compensate for the vibration of the image. Larger magnifications require a steady hand or tripod. The diameter of the exit pupil also plays an important role. The exit pupil is the size of the beam of light that leaves the binoculars and enters your eyes. The larger the light beam, the brighter the image and the more you will enjoy using the binoculars. The magnification comes at the expense of the diameter of the exit pupil.

4 Width of the field of view

Generally speaking, the larger the magnification of the binoculars, the narrower the field of view will be. However, there is no firm connection between the magnification and the width of the the field of view. In general, good binoculars have a wider field of view than average ones with the same magnification.
The field of view is normally expressed in 'metres at a distance of 1,000 metres' or 'm/1000m'. Sometimes the imperial measurements of 'feet at a distance of 1,000 yards' or 'ft/1000yd' is used. If you divide this figure by 3, you will get the field of view in 'm/1000m'.
Sometimes the field of view is expressed as an angle. The conversion of this to metres is somewhat more complex.

5: Porro prism or roof prism binoculars?

Roof prism binoculars are mostly sold in the higher segment nowadays. As far as construction is concerned, they are more expensive than porro prism binoculars, but they are also more compact and more airtight. They are more airtight because the volume of the binoculars does not change when focusing the binoculars.
The advantage of porro prism binoculars is that the image obtained generally has more depth and clarity.

You can recognise roof prism binoculars by the fact that the ocular lens (the lens through which you look) is in line with the front objective (lens). In porro prism binoculars, these lenses are not in line with each other.


ROOF PRISM BINOCULARS	PORRO PRISM BINOCULARS

6: Optical quality of the binoculars

The optical quality of binoculars depends on a number of things, such as the material used for the lenses and prisms, the coatings, the construction of the binoculars, but above all, the quality and care taken in grinding and polishing the lenses and prisms and aligning them correctly. Unfortunately, the latter two points just mentioned are not included in the product specifications of the binoculars, which means that you will have to rely on your own observation or recommendations from others when purchasing your binoculars. Optical quality is determined by many things, such as brightness, clarity, contrast, edge sharpness, colour rendition, bias and non-squint, among others. In the case of a squint, the image moves when you first look with your right eye and then with your left eye. Your brain is able to correct a minor deviation, however, this may cause eye strain.

7: Mechanical quality and warranty

When buying binoculars, of course you should also pay attention to the mechanical quality of the binoculars, as well as the warranty. Problems seldom occur in more expensive binoculars but cheaper binoculars sometimes have defects, such as cracked eye cups (rubber eye caps), and parts that are either loose or too tight and are consequently difficult to rotate.
In addition, you should also pay attention to the fact that 'nitrogen filled' does not always mean 100% nitrogen filled. During the manufacturing process, the binoculars are purged with nitrogen (sometimes also with argon) to expel any possible moisture. However, some residue could remain which could cause internal condensation in extremely cold weather conditions.
A warranty is all well and good, however, you should also be able to rely on good service if there is anything wrong with your binoculars. A short-term warranty is a sign that something may not be right. A long-term warranty, however, does not necessarily mean that you are getting a top-quality product. A long-term warranty plus a reliable supplier are the best guarantee!

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