Cobra Griffon night vision
Equipment Review for Wildlife Britain
© Cobra
It's an incredible experience, sitting in the middle of a forest on a dark October evening, surrounded by the guttural roars of testosterone-charged deer stags. You can hear them stumbling around just a few feet from you, but you can't see them. Or can you?
When originally developed just before World War II, night vision equipment relied on powerful infra-red lamps to illuminate the subject. However, as the enemy forces also began to adopt night vision equipment, it became easy to look for the other force's IR lamps and use them for target practice. Clearly, a better system was needed.
Today's consumer-level night vision equipment is a continuation of the systems phased in to military use during the 1960s, known as Generation 1 (Gen 1). These systems are effectively image intensifiers, and rely on at least some light being available to produce an image.
Light entering the device through the objective lens at the front is focused onto the photocathode part of the intensifier tube. Stimulated by the light photons, the photocathode emits electrons into the intensifier tube, which are multiplied and accelerated by a microchannel plate. The microchannel plate, a glass disc with millions of microscopic holes, has electrodes on either side and a high-voltage current from the device's power supply applied across them. As each electron strikes the microchannel plate, thousands of other electrons are released into the intensifier tube, creating a chain reaction that results in many more electrons emerging from the end of the tube than originally entered. These multiplied electrons strike a phosphor screen at the end of the tube, producing an image that we can see through the ocular lens at the other end of the night vision device.
Later generations of devices (Gen 2 and Gen 3) are sensitive to a wider spectrum of light and can provide a higher gain, resulting in a clearer, brighter image with greater resolution. However, Gen 2 devices are too expensive for all but the most dedicated night-owl, and Gen 3 devices are currently restricted to military applications. That leaves Gen 1 devices to make up the bulk of those available to consumers.
As these night vision devices merely amplify available light, they can't work by themselves in complete darkness. However, because they amplify both visible and invisible light, the clarity of a subject can be increased by illuminating it with an infra-red light source.
And, to boost the range as well as its usefulness, the objective lens at the front of the device generally incorporates a magnification factor. The choice of magnification depends largely on the purpose of the device.
For our purposes, we wanted a reasonable level of magnification, built-in IR illumination of some kind, and strong, robust build.
Cobra Optics is the UK's best known brand of night vision equipment, and their range spans more than 30 models for a number of different applications. We chose the Cobra Griffon, a mid-range monocular with a high-grade Gen 1 tube, 3x magnification and built-in IR illuminator.
Powered by a single CR123A lithium battery, the unit offers two separate switches for power and IR illuminator. The illuminator itself has an adjustable beam, to provide either a wide spread of infra-red illumination or a more focused spot.
The unit is housed within a tough plastic bodyshell, with the objective and ocular lenses coated in wear-resistant rubber. The unit weighs 690g and is supplied in a soft case. The objective lens cover, which has a small central hole to allow the unit to be tested in brighter conditions (do not turn the unit on in daylight!) is tethered to the unit to stop it getting lost. One side of the bodyshell is moulded to fit comfortably in your hand (assuming you're right handed) and incorporates a strap to keep things secure.
All sounds fairly positive so far, doesn't it?
If you've never used night vision equipment before, you might find yourself quickly becoming disappointed.
© A Kefford
The first disappointment is in the quality of the image produced. The fact that the image is green should be no surprise to anyone who's seen any recent Hollywood spy film (green is used because the human eye can interpret more shades of green than any other phosphor colour). However, the sharpness of the image falls off rapidly towards the edges, leaving only a small area in the centre of the screen that produces a realistically useful image.
In addition, the manufacturing process involved in the production of the intensifier tubes can leave several black dots on the phosphor screen. All units will have these black dots present to some extent, and each manufacturer sets out a policy of how many dots are allowed in a specific location, and of what size, before the tube is rejected. Whilst the dots present on our unit didn't detract too much from the overall quality of the image, those expecting a perfectly uniform picture would do well to be aware.
The biggest area of disappointment is in the physical operation of the unit. With an f/1.7 lens, the image generated by the unit has such a small depth of field that anything not in sharp focus becomes difficult to make out, quickly losing all detail. This makes scanning, say, open heathland for wildlife, practically impossible without continually refocusing and rescanning the area. To compound this issue, the objective lens requires so many turns from one focus lock to the other that keeping up with subjects moving at anything other than a slow crawl is, again, almost impossible.
Remember that you do not look through the unit, but instead your eye focuses on the screen at the rear of the intensifier tube. The ocular lens has an equally large degree of focus travel, and adjusting the image into sharp focus can be quite tricky.
Add in the ocular lens's habit of refocusing itself if anything brushes against it (every time you place the unit in its protective pouch, for instance), and you have an expensive toy that quickly becomes frustrating at the very moment you need it to perform.
We should be clear, however, that nearly all night vision monoculars on the market behave in the same fashion, and these issues are not restricted to the Cobra alone.
But those expecting consumer-level night vision gear to be the panacea of their sight-at-night problems, would be better advised to spend their £200 on carrots instead.
The Cobra Griffon is available for around £219.00.