Night Vision Optics
Night Vision Optical Techniques
The words “night vision optics” brings up images of spies or Special Forces agents using bulky, futuristic-looking goggles to lay eyes on the bad guys in the dead of night without being seen. The cool part is, unlike most things in spy movies, night vision goggles really do work pretty much as well as you see in film, and they are surprisingly easy to purchase and use yourself.
Methods of Night Vision
There are two main forms of night vision. Image intensification is what most people picture: the green-and-black image that almost looks like you’re viewing the world entirely with a green flashlight. Most image intensification devices are used by the military and police forces, but some models are freely available for the public to purchase. The focus of these devices is amplification of very low levels of light in the environment.
Thermal imaging is another very popular night vision resource: while it might not highlight environments or surfaces quite as well as image intensification, it detects heat, so picking out warm bodies or hot equipment is simple. Thermal imaging detects entirely infrared light (emitted as heat), so no visual light need be present in the environment at all.
Thermal Imaging
Creating a thermal image begins with the scene of the image you wish to view. All objects in the scene will emit some amount of infrared light from the heat they exude. This infrared light is picked up by a special lens that focuses it onto an infrared detector in the night vision device. This scanned light is interpreted by the detector and formed into a pattern known as a “thermogram.”
This thermogram is interpreted by a circuit board in the device, and the circuit board outputs a visible image to whatever monitor is being used (whether it’s a remote location as with a security camera, or contained in the same device, as with night vision goggles). Standard thermal imaging equipment can distinguish between temperatures of less than half of one degree Fahrenheit.
Image Enhancement
Image enhancement is what comes to mind first when most people mention night vision. The core of an IE night vision device is what is known as the image-intensifier tube, which serves to collect and enhance the effect of what infrared and visible light are in the environment.
The process starts at the objective lens, which captures as much light as it can from the scene. Most of this is ambient visual light, with a bit in the near-infrared part of the spectrum. This light is forwarded to the photocathode, which transforms the photons from the collected light into elections.
Here’s the magic: the electrons pass through a microchannel plate, which is a tiny glass disc with millions upon millions of extremely tiny holes in it. When a single electron emitted by the photocathode hits the microchannel plate, it excites atoms in the plate and causes more and more electrons to be emitted, which collide with the plate more and excite even more electrons. This effect, called a cascaded secondary emission, means that thousands upon thousands of electrons are emitted out the other side of the MCP where only one entered.<p>
These thousands of multiplied electrons collide with a screen coated with phosphors. The emitted electrons, while greater in number, retain perfectly their original alignment from the original photons that entered the lens: once they reach the phosphor screen, the electrons excite the phosphors and cause them to release photons that travel out the other side of the image-intensifier tube. The user can finally see the image through an ocular lens, where they can zoom and focus just like any standard camera lens.
The words “night vision optics” brings up images of spies or Special Forces agents using bulky, futuristic-looking goggles to lay eyes on the bad guys in the dead of night without being seen. The cool part is, unlike most things in spy movies, night vision goggles really do work pretty much as well as you see in film, and they are surprisingly easy to purchase and use yourself.
Methods of Night Vision
There are two main forms of night vision. Image intensification is what most people picture: the green-and-black image that almost looks like you’re viewing the world entirely with a green flashlight. Most image intensification devices are used by the military and police forces, but some models are freely available for the public to purchase. The focus of these devices is amplification of very low levels of light in the environment.
Thermal imaging is another very popular night vision resource: while it might not highlight environments or surfaces quite as well as image intensification, it detects heat, so picking out warm bodies or hot equipment is simple. Thermal imaging detects entirely infrared light (emitted as heat), so no visual light need be present in the environment at all.
Thermal Imaging
Creating a thermal image begins with the scene of the image you wish to view. All objects in the scene will emit some amount of infrared light from the heat they exude. This infrared light is picked up by a special lens that focuses it onto an infrared detector in the night vision device. This scanned light is interpreted by the detector and formed into a pattern known as a “thermogram.”
This thermogram is interpreted by a circuit board in the device, and the circuit board outputs a visible image to whatever monitor is being used (whether it’s a remote location as with a security camera, or contained in the same device, as with night vision goggles). Standard thermal imaging equipment can distinguish between temperatures of less than half of one degree Fahrenheit.
Image Enhancement
Image enhancement is what comes to mind first when most people mention night vision. The core of an IE night vision device is what is known as the image-intensifier tube, which serves to collect and enhance the effect of what infrared and visible light are in the environment.
The process starts at the objective lens, which captures as much light as it can from the scene. Most of this is ambient visual light, with a bit in the near-infrared part of the spectrum. This light is forwarded to the photocathode, which transforms the photons from the collected light into elections.
Here’s the magic: the electrons pass through a microchannel plate, which is a tiny glass disc with millions upon millions of extremely tiny holes in it. When a single electron emitted by the photocathode hits the microchannel plate, it excites atoms in the plate and causes more and more electrons to be emitted, which collide with the plate more and excite even more electrons. This effect, called a cascaded secondary emission, means that thousands upon thousands of electrons are emitted out the other side of the MCP where only one entered.<p>
These thousands of multiplied electrons collide with a screen coated with phosphors. The emitted electrons, while greater in number, retain perfectly their original alignment from the original photons that entered the lens: once they reach the phosphor screen, the electrons excite the phosphors and cause them to release photons that travel out the other side of the image-intensifier tube. The user can finally see the image through an ocular lens, where they can zoom and focus just like any standard camera lens.