|
Binoculars Explained...
Safety first!
Never look at the Sun through binoculars, telescopes or any other optical
equipment.
FAQs
Binoculars Explained
Roof prisms
Porro
prism
Magnification (power)
Objective lens (diameter)
Exit pupil
Field of View
How to focus
centre focus binoculars
Cleaning the binoculars
Binoculars Explained
Binoculars
are really just two small telescopes mechanically linked together. All of the
facts and formulas that help you to understand telescopes also pertain to
binoculars.
A good pair of binoculars is one of the
handiest accessories. So whether you want to get a better view of the
local football game, or find a bird in the countryside, a good pair of
binoculars is often indispensable.
back to
top^
Prisms
are what let you see a correctly oriented image when you
look through a pair of binoculars. There are two types of prisms in common use,
Porro prisms and roof prisms.
Roof
prisms
are essentially in line inside the
optical tubes, and make for a more compact set. Roof prism
binoculars have straight tubes (the front/objective lens is in line with the
rear/ocular lens), and are therefore more compact, an important consideration
for the sportsman. They usually have two pivot points between the tubes, and are
more difficult to adjust to the spacing of your eyes. Roof prisms can give an
optical image equal to the best Porro prisms
back to top^
Porro prism
can be identified by their offset tubes; the
objective lens is not in line with the ocular lens. The front lenses are usually
closer together than the rear lenses, but the reverse can also be true,
particularly in compact models. The Porro prism design is usually optically
superior to the roof prism design, especially in medium priced class binoculars.
Porro prism have a single pivot between the two halves of the
binocular, and are therefore easy to adjust for the distance between your eyes.
Lens coatings
These coatings assist light transmission. They are what produce
the blue, red, or green reflections you see when you look into the front
(objective) lens of a pair of binoculars.
The latest fad in coatings is ruby or red multi-coatings. These
are intended to reduce glare in bright light
back to top^
Magnification (power)
are commonly described by
using a pair of numbers, as in "7x50" or "8x25." The first of these numbers
refers to the magnification offered by the binocular. Magnification is why most
people buy a pair of binoculars explained in the examples above, "7x" means the binocular
makes whatever you look at appear seven times closer than it does to the unaided
human eye.
Remember that everything (including
movement) is magnified when you look through a pair of binoculars, especially
your own shakes and tremors. So the higher the power, the harder it seems to
hold them steady. The higher powers sound like a good deal, but
often result in jiggly, blurred views. This is why 7x 50 are chosen by
so many experts, including the military
back to top^
Objective lens (diameter)
The second number most commonly associated with binoculars
refers to the diameter of the objective lens in millimeters. Thus in "7x50," the
"50" means that the front lenses are 50mm in diameter, which
is large for hand held binoculars.
This is very important information, because
the larger the diameter of the front objectives, the more light can enter the
binoculars and be focused to your eyes. Thus, other things being equal, you can
see better in dim light binoculars that have large front lenses. For
example, 7x50 are often called "night glasses" because they seem so
bright in dim light.
back to top^
Exit pupil
The magnification and the diameter of the objective lens
determine the size of the exit pupil. The diameter of the exit pupil determines
how much light is transmitted to your eye.
The actual diameter of the exit pupil is
easily computed. Divide the diameter of the front objective lens (in millimeters)
by the magnification of the binocular. For instance, take a pair of standard
size 7x50 binoculars. Divide 50 (the diameter of the objective) by 7 (the
magnification) and you get approximately 7.1 (50/7=7.1). 7.1mm is the diameter
of the exit pupil for 7x50 binoculars.
back to top^
Field of View
The field of view is the area seen
through your binoculars. It is properly measured in degrees. The larger the
field of view the more area you can see. Field of view is particularly important
when observing moving subjects, like animals or birds, or at sporting events
How to focus centre focus
binoculars explained
Aim your binoculars at something in the
distance. Close the right eye (or cover the front of the right tube), and focus
the left side of the binocular to your left eye using the centre focus control,
which is concentric with the pivot shaft between the binoculars. (Note: the left
eyepiece itself does not focus on centre focus.) Next, close your
left eye (or cover the front of the left tube), and focus the right eyepiece to
your right eye. DO NOT touch the centre focus control while you are focusing the
right eyepiece to your right eye. Now you are finished. What you have just done
is adjust the binoculars for your individual eyes.
back to top^
Cleaning the
binoculars
Use a soft lens brush or a soft,
lint-free cloth to clean the binoculars. If you use a cleaning
agent, never apply the the liquid to any of the glass surface, but sprinkle it
on the cloth.
back to top^
| 
