Good binoculars provide superior clarity and
image quality with the least distortion and discoloration.
Things to consider when buying binoculars 1. Minimum magnification should be 7x35. Larger
multiples of 8x, 9x, or 10x each give a larger image. You
might find 10x binoculars can be rather unwieldy since they
get heavier as they go up in power.
The first number given is the power of magnification, and the
second number is the size of the front or objective lens. For
example in 7x 35 the image will appear 7 times closer. The
lens diameter will be 35 millimeters. A larger lens lets more
light in and give you a clearer image. Get the highest power
you can keeping in mind that there can be a large weight
difference and you may get tired carrying heavy binoculars
around. Because birds are small, and often in shaded
areas it is desirable to have a wider objective lens, allowing
more light in for a brighter image.
2. Test to see if the barrels of the binoculars flex
fairly easily. They should move easily but if you hold them
out they should not move by them selves.
3. Make sure you can bring the barrels of the
binoculars close enough together so that the image you see
merges into a single, clear image within a single, perfect
4. Some binoculars do not focus on objects up close,
so you may miss a fleeting bird. Try to focus on something
close. While doing this also check to see if there is any
distortion in the image. Poor quality binoculars may
5. The exit pupil is another thing to consider. The
exit pupil is the diameter of the image as it leaves the
eyepiece lens. If the exit pupil is smaller than your eye's
pupil diameter the image may appear dark and less clear. A
binoculars exit pupil should be 4 mm or above for general
daylight use, or 6-7 mm for low light viewing. To determine
the exit pupil of a pair of binoculars, divide the size of
the objective lens by the magnification. For 7x35 binoculars
we would divide 35 by 7 and find that these binoculars have
an exit pupil of 5 mm, a good size for general bird watching.
6. Lens coating will provided
better contrast and image quality, as well as extending the
life of your binoculars.
Learning to use your new binoculars
In bird watching you are trying to spot small objects that
move very fast. The best way to see a bird is to first focus
on it just with your eyes. Then without loosing focus bring
the binoculars up to your eyes. You can easily practice this
before going on a bird watching trip.
Also, look for a pair with a rubber casing. These are more
resilient to nicks and scratches and better able to withstand
the jolts that can throw some binoculars out of alignment
Eye relief is important if you wear glasses is. Eye relief is
the maximum distance in millimeters that your eyes can be
away from the eyepieces and still see the whole picture. Most
glass wearers need extended eye. Binocular manufacturers try
to provide this relief through the use of rubber eyecups that
can be rolled down. Often this is not enough! Some binoculars
are constructed with extended eye relief for glass wearers.
How Optics Work
Inside the binoculars or telescope is a series of glass
lenses. The lens nearest the eye is known as the eyepiece.
The lens farthest from the eye is known as the objective
lens. Inside the housing between the eyepiece and the
objective lens are combinations of other lenses and glass
prisms. These are used to magnify or bend light. A longer
light path gives more magnification.
In binoculars reflecting the light into a folded path using a
pair of prisms increases the length of the light path.
In a telescope magnification power is increased by increasing
the length of the lens.
If you are viewing waterfowl, shorebirds, and perched birds
of prey a telescope is great. You have more power than
binoculars will give you letting you see much farther.
A reasonably priced telescope with a zoom eyepiece and
magnification ranging from 20x to 45x is a good place to
start. Add a lightweight, sturdy tripod that easily extends
to eye level.