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Chuck Husick: Techno-Talk, January 2005 from BoatUS Magazine - Updated July 2009

Night Scopes

Sailing 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 aids).

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 secondary role.

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.

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