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to choose binoculars most suitable for your needs
This article has been written to help you learn how to
evaluate binoculars and then show you how to choose binoculars based
on your budget and the purpose for which you plan to use them.
We shall be looking at how binoculars work. Understanding this will
help you to understand the different factors that will affect price
and the features that are available - usually these revolve around optical
quality, magnification power, and portability – before moving on to
look at different price categories and justifications for buying a more
expensive pair depending on what they will be used for.
The overall aim is to prepare you for the task of finding the right
pair of binoculars, at the right price, without compromising on features
that you may require.
How Binoculars Work
Essentially, all binoculars are derived from classical telescopes,
which consist, in their most basic fashion, of two lenses. The lens
nearest whatever is under scrutiny (objective lens) provides an image,
which can then be enlarged by the lens nearest the viewers eye (eyepiece
lens), by moving it closer or further away from the objective lens.
A pair of binoculars can be seen as two such telescopes, side by side,
which together produce an image which has the depth of field that we
are used to, rather than just a large flat image.
Since the light has been refracted (bent) as it has been directed through
the lenses, by the time the viewer sees the image it is back to front,
and upside-down. To correct this, two prisms are placed inside the binoculars,
between the objective and the eyepiece. It is the presence of these
four prisms in the shoulders of the binoculars that give them their
Light and Weight
The power of the optics is expressed as two numbers, such
as 7 x 35. The first is the number of times magnification, and the second
is the diameter of the objective lens. A larger objective lens makes
sense during low light conditions, since it can capture more of the
The magnification factor tells you how many times larger the object
will be magnified – a number of between 4 and 7 is ample for most applications.
Any larger than about 9 or 10, and the natural shake of the human hand
will be magnified to such an extent that the image becomes difficult
to see, and a tripod will be required.
Glass also has a tendency to reflect as much as 5% of the light that
arrives at its surface back towards the light source. A simple coating
was devised to prevent this, by allowing more light to pass through
the lens, and less to be reflected back. Since the advent of the original
coating, the technique has been refined, and there are several grades
of lens coating available.
The best result is achieved when multiple layers of coatings are applied,
to the front and rear of the lens. Each coating is designed to provide
the maximum transmission of light through the lens, and minimum reflection
and diffraction, resulting in a brighter, clearer picture than with
standard non-coated lens models.
Modern lightweight binoculars have also evolved in terms of the use
of roof prisms, rather than the traditional Porro prisms. This means
that they have no ‘shoulders’ and look more modern. The lack of superfluous
casing makes them easy to carry, and substantially lighter than traditional
binoculars, however the price tag for higher power models tends also
to be more substantial than for the traditional type of a similar magnification.
When considering how to choose binoculars price is a major
consideration. There are several factors that will affect the price.
The first is the type of lens and coating that is used; glass lenses,
which are coated on each side with multiple layers, will produce a picture
at high magnification which is substantially clearer and brighter than
that produced by plastic lenses.
Plastic lenses, on the other hand, tend to make the binoculars lighter,
but will be substantially more expensive for the same grade of picture
quality. If the binoculars are to be used in clear conditions, at a
low power, then this may be acceptable. If more variation in lighting
(i.e. dusk and night use) is expected, then one should opt for better
quality optics, and hence a higher price tag.
The build quality will also affect the price. More rugged, shock-proof
binoculars destined for use in harsher conditions (marine or backpacking)
will cost more than those which do not need to be waterproof or shockproof.
Before you decide how to choose binoculars you need to
consider the solutions for differing environments. Single scopes or
spotting scopes, for example, are often used for hunting. Here, since
they are, in effect, half the size of a regular pair of field glasses,
better quality optics can be afforded, as the cost will be proportionally
Hunting glasses need to be good in all light conditions, from dawn to
dusk, and even have limited night vision. In general they should be
lightweight, but probably with a smaller magnification, and larger objective.
High power spotting scopes, or binoculars, where the power exceeds 10x
will need to be mounted on a tripod. The best models will be ones with
a very large objective lens, suitable for use in many conditions, but
will be too heavy and cumbersome for use on the move.
Finally, if you are going to do hiking while hunting, it is important
to note that optics are very fragile, and so plastic lenses over glass
ones, and a rugged case are probably going to be more important than
high power, or the ability to use them at night.
As a curio, it is possible to buy, from Zeiss, a pair of binoculars
which have a mechanical anti-jog mechanism which allows for extremely
high magnification, but without the shake associated with it. They come
in at around $4000.
Digital binoculars are a cheap alternative, and can be picked up for
considerably less ($200), and usually have a built-in camera. They are
not perfect optically, with a resolution of around 3 mega pixels, but
will suffice for the hobbyist.
There are many different terms that are bandied about when
reading descriptions of binoculars and before rushing off to the store,
it is worth understanding some of the more esoteric ones.
For example, there are several different descriptions of the coating
that has been used (see Power, Light and Weight) to reduce the amount
of light reflected back through the lenses during magnification:
▪ C : Some surfaces coated
▪ FC : All surfaces coated, except plastic lenses
▪ MC : Some surfaces have been coated in multiple layers
▪ FMC : All glass surfaces are coated with multiple layers.
In the last case, one would expect a good quality piece of optics to
be able to transmit between 92% and 95% of all available light back
to the eye.
The “Exit Pupil” is also important and can be calculated by dividing
the power by the objective size and yields a value which is very important
– it is the diameter of the light fed to the eye. Given that the average
human pupil ranges in size from 2mm to 7mm depending on the available
quantity of light, it is clear that, in the sun, an Exit Pupil value of 4mm (for example) will mean that 50% of the
image returned to the eye is lost.
By a similar token, if the value is smaller than 7mm for a night scope,
then it is not taking advantage of the human anatomy. A word of advice
– always use night scopes in the dark, to keep the pupil as wide as
possible; this means no, or very low, light around the place that you
choose to hide out whilst communing with nature.
Finally, if the phrase ‘Eye Relief’ is mentioned, then it refers to
the way that the eyepiece is set up with respect to the other optics
in the device. Most glasses will come with eye relief between 9mm and
13mm, and is the distance from your eye to the lens before your field
of view becomes limited.
If you wear eyeglasses, then eye relief above 14mm becomes desirable,
since you will already have a certain amount of distance between your
eye and your eyeglass lens, which you can not change. Given this, if
your chosen optical device has a small eye relief, then you will have
a very restricted field of view, and miss out on most of the picture!
As you can see when you need to decide how to choose binoculars most
suitable for you there are many aspects to consider. Hopefully this
article will have made your job easier. For more information on the
binoculars available you can visit the relevant links.
Guy Lecky Thompson is a successful freelance writer offering
guidance and suggestions for consumers regarding how to choose binoculars,
telescopes, night vision
and spotting scopes.
His many articles give information and tips to help people save money
and make smarter decisions.