INSTRUMENTS
Key Points to keep in mind:
Exit pupil:
The
exit
pupil
is
the
bright
circle
as
seen
on
the
surface
of
the
eyepiece
from
about
30
cm
away
when
you
point
the
objective
lenses
toward
a
bright
light.
Simply
put,
the
bigger
the
exit pupil,
the
brighter
the
image.
The
diameter
of
exit
pupil
is
calculated
usinq
the
following equation:
 |
Diameter
of
exit
pupil |
 |
Binocular
brightness
depends
to
some
extent
on
the
diameter
of
the
human pupil.
If
you
use
binoculars
with
an
exit
pupil
diameter
nearly
the
same
size
as
your
own pupil,
the
light
entering
the
binoculars
will
reach
the
eye
most efficiently.
As
a
human
pupil
normally
opens
2
to
3mm
in daylight,
binoculars
with
an
exit
pupil
of
around
3
mm
will
provide
sufficient brightness. (Refer
to
Fig.
2.)
|
| However,
the
human
pupil
extends
to
about
7mm
in
the dark,
so
binoculars
with
an
exit
pupil
diameter
of
around
3mm
provide
insufficient
light
in
the dark,
resulting
in
a
dark
image. (Refer
to
Fig.
3.) |
 |
 |
Binoculars
with
an
exit
pupil
diameter
of
around
7mm
are
thus
best
suited
to
astronomical
observation
and
night
surveillance.
|
Relative brightness:
Relative
brightness
is
obtained
by
squaring
the
exit pupil,
As
with
the
exit pupil,
the
greater
the
relative
brightness
the
brighter
the image.
| .Look
at
the
exit
pupil
on
the
surface
of
the
eyepiece
from
about
30
cm
away
and
check
if
it
is
perfectly
round.
Some
binoculars
available
on
the
market
have
an
imperfectly
round
exit pupil,
due
to
improper
prism material.
This
will
cause
loss
of
light,
resulting
in
reduced
image brightness.
Needless
to say,
the
exit
pupils
on
Nikon
binoculars
are
all
perfectly
round
and clear. |
| Perfectly
round
exit pupil
|
Shaded
exit
pupil |
|
Effective
aperture
of
the
objective lens:
The
effective
aperture
is
an
opening
of
the
objective
lens
through
which
light
can
pass
without eclipse. Generally,
the
inner
diameter
of
an
objective
lens
is
specified
as
the
effective
aperture. However,
some
manufacturers
show
only
the
diameter
of
the
objective
lens
as
the
effective
aperture
of
that lens,
although
the
actual
effective
aperture
is
smaller
than
the
value shown.
Remember,
the
larger
the
effective
aperture,
the
greater
the
resolving
power,
and
the
brighter
the
image.
But
increasing
the
effective
aperture
of
an
objective
lens
means bigger,
heavier binoculars.
An
effective
aperture
of
50mm
is
generally
the
limit
for
manual operation.
Systems of prisms
The lenses determine the factor of
enlargement. The prisms guarantee that the image that you see is in the good
direction (and not an image out of mirror), According to the series, the
binoculars can use a system with prism of Porro, where the frontal lens and the
eyepiece are shifted, or a system with prism in roof technically more
sophisticated. The premiums are laid out one behind the other, which makes the
binoculars more compact and lighter.
Lens coating:
 |
Light
reflection
differs
in
coated
and
uncoated
lenses |
Lens coating plays an important role in improving image
brightness. When light passes through a lens, some light is reflected by the
front and rear surfaces of the lens. This light causes flare or ghosting,
reducing image sharpness and contrast. Vacuum-vaporized coating puts a thin,
transparent film on the lens surface which minimizes these adverse effects.
|
wihout coating
|
One layer coating |
multi layers coating |
Most binoculars incorporate multilayer coated
lenses covering a wide range of light wavelengths, ensuring brilliant, clean
images even in dim light.
Transmission factors for uncoated lens surfaces, lenses with a single
coating, and lenses with multilayer coating are shown in the following table.
Since several lenses and prisms are used in binoculars, differences in
transmission factors become greater as the number of lenses increases. (See the
table below.)
French