naw braw it just makes more photon
You act as if that's a bad thing, @AnimalsRock
That said, unless you are using something military grade, a night vision camera will be just an IR sensor and an active IR light. In fact, many /normal/ camera sensors, such as the one in your cell phone, are sensitive to IR light. There probably is a filter that blocks it, though, because for everyday pictures you do not want any IR component in them, or else it may look weird. But consider your cell phone a night vision camera, it is most likely damn close to being one.
Glass is not transparent to IR light at the wavelengths we are typically trying to detect, so you use special materials for the optics. And probably the biggest issue is that you have to cool down the entire apparatus. That is because if you are trying to capture the light of a scene at 20C and your camera is also at 20C, that means that your camera itself is shining as brightly as the objects you are trying to photograph, and thus will never work.
The former method is much easier to implement, basically that is a flash, but in infrared and so you can't see it with the naked eye. The second method is much more sophisticated, because the infrared radiation of object at similar temperature will look similar as well, and the intensity is low. But it has the advantage of being undetectable, because it does not actively shine any light onto the scene.
For dark scenes, such as astronomy, you would typically use a sensitive sensor and good amplification circuitry to measure the few photons that hit your sensor accurately. The other option, for truly "see in the dark" cameras is that they either actively illuminate the scene with infrared light, which bounces off and is picked up by the sensor, or they capture infrared light that is emitted by any warm object passively.
Buki, I am either horribly misunderstanding what you mean, or I disagree. Night vision cameras at no point convert electrons back into photons. The basic principle of a photodetector, as in, a single pixel of a camera sensor, is that of a solar cell. A photon hits, releases electrons, those are picked up and electrically amplified.
Didnt see this blowing up or anything, i might try to make a display for it.