Chuck Husick: Techno-Talk, January 2005 from BoatUS Magazine - Updated July 2009
at night can be awe-inspiring, especially on a clear, moonless night
when the sky is filled with countless stars. Unfortunately the electronic
navigation aids that we value so highly also prevent us from seeing
the night sky as well as those who sailed when the only source of light
on a boat was a dim candle or oil lamp (or, for that matter, unlit navigation
Mariners of yore benefited from what is known as “dark adaptation,”
the ability to see in almost total darkness that occurs when the eye
adapts to very low light or no light over a period of an hour or two
(by a factor of 20,000 to 1). Today, the light from the screens of our
radar, chart plotter and sonar displays robs us of our dark adaptation.
Fortunately the electronic technology that deprives us of enhanced night
vision can be used to restore and even surpass nature’s process
of dark adaptation. The electronic light amplifier in a night scope,
for example, can turn night into day.
All night scopes operate similarly. An objective lens focuses the available
light on a phosphor screen (photocathode) that converts the incoming
light photons into electrons. Energy supplied from the device’s
battery powers circuitry that multiplies and accelerates the image from
the phosphor screen, focusing them on a second phosphor screen where
they are reconverted into visible light.
The scope’s ocular lens delivers an intensely amplified, somewhat
ghostly green image of the scene to your eye. (Eye, not eyes, due to
the cost of the light amplifier most civilian night scopes are monoculars).
Light amplifiers similar to those used in marine night scopes produce
the green scintillating, images of nighttime battlefield conditions
often shown on TV.
Monocular night scopes are available at prices ranging from less than
$100 to well over $3,000. The price and performance of the device is
primarily determined by the type of light amplifier used, with the quality
of the lenses and the overall construction playing an important but
The least costly units use vacuum tube “Generation I” light
amplifiers and are most often made in Russia. Although prices begin
at about $100, night scopes suitable for use on a boat typically sell
for $250-$350. The light amplification capability of these units is
on the order of 10,000:1.
Scopes that offer the least magnification and therefore the widest field
of view are the most desirable. The narrow field of view that accompanies
higher magnification might help you identify a distant marker, however
you might not see the nearby object you are about to run into, diminishing
the value of both the scope and your boat.
The better, and substantially more expensive Gen II or Gen III scopes
sell for between $1,400 and $2,200. The light amplifiers in these units
use a device called a channel plate amplifier in place of the vacuum
tube used in Gen I units. They provide greater light amplification (as
much as 35,000:1). Their optics provide 1:1 viewing, a wide visual field
and less visual noise. Gen II and Gen III units are also better able
to respond to changes in light level, especially if accidentally exposed
to a really bright light source that might temporarily blind a Gen I
unit. The useful life of Gen 2 and Gen 3 light amplifiers is usually measured in thousands of hours whlle some of the low price Gen 1 amplifier tubes may work for only a few hundred hours. (However most recreational mariners will need to use their night scopes for only a few hours each year, promised lifetime need not be a deciding factor).
The photocathode in the night scope that converts visible light into
electrons is sensitive to both visible light and some infrared radiation.
Objects that are warmer than their surroundings may be more visible
than those at ambient temperature. Living foliage will usually appear
brighter than other objects, a technique used to defeat efforts at camouflage.
The beam of normally invisible infrared light from your TV remote control
will be clearly visible when viewed using a night scope. Many scopes
include an infrared light source so that close up areas can be illuminated
and viewed without need for a visible light. Don't expect the infrared illuminator built into some of the units to provide a useful image beyond about 10 to 15 feet, however the infrared energy emitted by many targets will make them visible at substantial distances even when there is very little or no visible light.
Although results vary, a Gen I scope will make a boat-size target visible
at about 150 yards on an overcast, moonless night, at 300 yards when
the stars are visible, 500 yards with a crescent moon and 750 yards
when most of the moon is visible. Gen II scopes will almost double these
numbers while a Gen III unit will provide an additional 25-50% increase
in visibility range. Many of the night vision devices that use Gen 2, 3 and especially Gen 4 image amplifiers may not be exported from the US, however in all but a few cases they may be carried on board a US registered vessel on a trip into foreign waters.
There are two ways to have the very best available Gen IV night scopes.
You can buy one for about $4,000 -$6,000 or join the military. I am told they
will be pleased to loan one to you when they think you need one.