In spite of the wide spread of prices and die range of different looks - from die family-friendly Night Force Marine to the frankly scary Cobra Tornado - die operation of all devices is pretty similar. There's a battery or two to be installed and switches to turn the image intensifier and infra red torch on and off. So long as you know where to find die switches - in the dark - that's almost all there is to it.

Fiddly focusing

Apart from focusing them, that is. Focusing, to be honest, is a bit of a palaver. The problem is that despite appearances, you're not really looking through a night vision device: you're looking at a screen. This means that if you see a blurred image you have no way of knowing whether it is because die image on die screen is blurred, because die objective lens is out of focus, or whether your view of it is blurred because die eyepiece needs adjusting. Solving die problem isn't just a question of twisting die eyepiece until it becomes sharp, as you would with an ordinary monocular. Most instruction manuals suggest that the solution is to adjust die eyepiece focus to suit your eye-sight first. This is why the lens caps of night vision devices all have a small hole or dark filter in the centre. The idea is that you leave the lens cap on and look 'across a room' in normal lighting while focusing die eyepiece to get die sharpest possible picture. Then, when it's dark, you can remove die lens cap and adjust die objective lens alone to focus on mote distant targets. When using goggles, of course, there are two eyepieces to be adjusted, but otherwise die procedure is much die same. Inevitably, each make and model had little differences.The ATNs and Cobras, for example, had the nicest battery-compartments. This is partly because they both use AA batteries - of which you probably already have plenty of spares on board - rather than the relatively unusual CR2s and CR123s, which will require a special trip to your local camera shop, and partly because they are particularly easy to get into, even in die dark and with cold hands. The Cobras set themselves apart from die others by having rotary switches: twiddling the switch through 45° switched the tube on and another 45° activated die infra red torch. It's a very good system, just so long as you're familiar enough with the equipment to be able to find the switch. The ATNs were different too: they used a single press switch, on which a short press switched die power on to the tube and a long press turned on the infra red light. All the Gen 1 units used separate push buttons, which were generally well positioned under die first and second fingertips. The only significant variation between them was that those on the NightForce Marine 2 had to be held down, while all the others had to be pressed a second time to switch off.