Binocular Basics - Los Gatos Birdwatcher

Binocular Basics - Los Gatos Birdwatcher
The Store for Nature Lovers
Binocular Basics
Binoculars are available in many
different sizes, magnification, and
price. The most important thing to do
when selecting a pair is to try them out
first. Consider what is most important
to you — weight, size, power,
eye relief (important for eye glass
wearers), close focus, waterproofing,
field of view, price. Consider how
the binoculars feel on your face (or
glasses) and how they feel in your
hands. What works for one person
does not necessarily work for another.
Most are waterproof and fogproof.
Most have multiple coatings on all
the air to glass surfaces. You can get
a good pair for $200, a great pair for
$600, and a dynamite pair for $1,000.
The best advice is to find a pair that
fits your criteria and your budget.
What to look for Look for good color contrast, side
to side clarity, and easy focus. To
check for its low light capabilities,
look under a parked car, and compare
the sharpness of each model. Try
different pairs and put them through
their paces. Using binoculars is not
intuitive; it takes practice. When you
put them up to your eyes, bring the
two barrels or lenses together so you
get one image. When trying to locate a
bird or other object, try to focus with
your naked
eyes on
the general
location and
then raise the
binoculars
to your eyes.
The chances
of seeing
your target
are much
enhanced.
When
describing
the location
of a bird or animal to another person,
look for close landmarks like rocks
and snags that are easily recognized.
If the bird is in a tree, use a clock face
to describe its location. Try to refrain
from “it’s over there” or “it’s in the
tree.” Another tip is to get behind
the person who is looking at the bird
and train your binoculars in the same
direction.
If you don’t like how your neck feels
after a day of hiking or birding with
a standard binocular strap, purchase
a harness that takes the weight
off your neck and puts it on your
shoulders. The Los Gatos Birdwatcher
recommends the “Bino-Strap” that
has wide elastic straps. 25.4 mm to the inch.) The larger the
objective lens diameter, the brighter
the image will be.
Optic Coatings Optical coatings are a microscopically
thin layer, or layers, of specially
formulated compounds that reduce
reflections. Every time light strikes
a glass surface, about 5% gets
reflected. The lens systems in modern
binoculars have between 10 and 16
glass surfaces which means that
you would lose well over 50% of the
incoming light. The light reflected
from the internal lens bounces around
inside the binocular creating an
optical “haze” that decreases image
contrast, especially noticeable when
viewing in “low-light” situations. The
real benefit of optical coatings does
not occur until all glass surfaces in
the lens systems are coated. Here are
some coating definitions: Coated Optics – At least one surface,
usually the outer surface of the
objective and sometimes the outer
surface of the eyepiece, has a single
layer coating. No internal glass
surfaces are coated. Fully Coated – All glass lens and
prism surfaces have a single layer
coating. Multi-coated – At least one surface,
usually the outer surface of the
objective and sometimes the outer
surface of the eyepiece, has a multiple
layer coating. The internal glass
Magnification x Objective surfaces
usually, but not always, have
single layer coatings. All binoculars are rated with two
Fully Multi-coated – All glass
numbers, the magnification and the
surfaces are coated with at least a
objective (big) lens diameter. For
single layer coat, and some surfaces or
example: a binocular rated 7x35 tells
all surfaces, have a multiple layer coat.
you that an object will appear to be
seven times closer than
Field of View with your naked eyes. Most birders
agree that an 8 or 10 power is the
Put your arms out in front of you
most useful. However, when you
and touch the tips of your thumb
go up in power, the field of view
and index fingers together to make
narrows, the light dims and shakes
a circle. Look at a specific object
are magnified. The number
across your yard through this circle.
35 tells you that the objective lens is
Everything you see within the circle is
35 millimeters in diameter (there are
in your “field of view.” Now slide your
fingers together to make the circle
smaller. The object you are looking
at doesn’t change, but the amount
of reference area around the object
appears less or narrows. Binoculars
have the same effect. The term for
how much reference area you can see
is field, or angle of view. There are
two units of measure for this term:
number of degrees or field within
feet at 1,000 yards. You can convert
degrees to feet by multiplying the
degrees by 52.5. For example: You
want to compare two binoculars, one
with a field of view of 5.5 degrees and
the other with a field of view of 7.5
degrees. The first binocular’s field of
view is 289 ft. at 1,000 yards while
the second binocular gives you a 394
ft. diameter circle at the same range,
a 36% bigger circle. If you use your
binoculars to scan for movement in
foliage or you use them to observe
birds on the wing, a wider field of
view will make your task easier.
Image sharpness overcome by using “long” eye relief
(13mm to 20mm) binoculars. Most
binoculars have twisting eye cups
that allow for some adjustment.
Because each person’s eyes are placed
differently, it is very important to
actually try out a pair of binoculars to
make sure they are comfortable.
Binocular Design
Binoculars range in size and weight
from compact (20-25mm and
9-13oz.), mid-size (32-45mm and
15-25oz.) and giant size (50-100mm
and 40oz and above.). The Los Gatos
Birdwatcher carries many styles in the
compact and mid-size range.
Compacts – These are designed to be
small and lightweight, something you
could carry around for several hours
without complaint. The small size
is achieved through the use of small
objective lenses, usually 25mm or less
in diameter. The smaller objective lens
tends to limit a compact’s use to welllighted conditions.
Image sharpness, in most binoculars,
decreases as you get to the edges of
the field of view. If you use a binocular
with a narrow field of view, more of
what your want to observe will be
towards the edges and could be less
sharply defined.
Mid-size – In this class of binoculars,
objective lens diameters are in
the 32mm to 42mm range with
magnifications of 7, 8, and 10 power.
Binoculars place a focused image at
a precise distance from the eyepiece
lens. The distance from the eyepiece
lens to this point is called the “eye
relief” and is measured in millimeters.
Most binocular’s eye relief is 10mm to
12mm. In order to get the full benefit
of the binocular’s field of view, you
need to place the binocular eye piece
at this distance. Built in eye cups on
many binoculars help maintain this
distance. However, many eyeglasses
or sunglasses wearers find that their
glasses prevent them from placing
the binoculars at the correct distance,
even after they have twisted the
eye cups down. This issue can be
Other Factors to
Consider
Binoculars & Eyeglasses
Giants – These are usually used for
astronomic viewing and get their
name from the size of their objective
lens (50mm to 100mm).
Lens Alignment – Binoculars are
precision instruments and even the
most expensive ones can get knocked
out of alignment during shipping. We
check all incoming stock for proper
alignment. It is always important for
you to try out the pair you want to
buy. An out-of-alignment condition
may show itself by the inability to get
both lenses focused or variations in
image sharpness or glasses.
Interpupillary Distance – This is the
distance between the pupils of your
eyes. All binoculars have a certain
range of adjustment (the central hinge)
to accommodate different people.
However, the range is based on the
average adult. If you are selecting a
binocular for a young birder, or your
eyes are very close together or very
far apart, you need to try out the
binoculars to make sure it fits.
Focusing – Always try focusing on
objects at various distances. The
action should be silky smooth and
provide a sharp image at all ranges.
Another important measurement to
birders is how close can you be to the
subject and still get a clear image?
The close focus distance should be
no more than 16 feet. Closer ranges
will allow you to study your subject in
great detail.
Diopter Adjustment – To allow
for the fact that most people with
uncorrected vision have one eye that
is weaker than the other, a binocular
has a mechanism (diopter) that allows
you to adjust the focus of one eyepiece
independently from the other. Usually
the right hand eyepiece will be marked
“+ 0 –” around the base which
indicates that this eyepiece has a
diopter adjustment. Set that eyepiece
to “0” and cover the right objective
lens with its lens cover or your hand.
Observe a subject through the lens
and use the central focusing wheel to
get a sharp image. Without changing
your distance from the subject or
moving the central focusing wheel,
move the lens cover or your hand to
the left objective lens and observe the
subject through the diopter eyepiece.
If the image is not sharp, rotate the
eyepiece right or left until you get a
sharp image. Remove the lens cover
or your hand and observe your subject
with both eyes. The image should be
very sharp and you should be able to
observe with no eye strain. You need
not change the diopter adjustment
unless your eye prescription changes
or someone moves the diopter control.
We hope to see you at the Los Gatos
Birdwatcher where our staff will be
glad to help you select your next pair
of binoculars!
Los Gatos Birdwatcher
King’s Court Shopping Center | 792 Blossom Hill Road, Los Gatos, CA 95032
hours: Monday–Saturday, 10am–6pm; Sunday 12pm–5pm
408-358-9453 | fax: 408-358-4673 | [email protected] | losgatosbirdwatcher.com |
Our mission at Los Gatos Birdwatcher is to educate, share adventures, and have fun through the love and experience of birds and nature.
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