155Views5Replies

Author Options:

How can a camera work if it films IR? Answered

If you film a remote control while pushing any button, you can see purple flashes of the IR LED, so most cameras can film IR. Why don't we have problems taking photos of hot things (people, boiling kettles, soldering irons, etc)? If I knew how to add a video I would have done it.

Discussions

Its  a question of wavelength - IR from remote controls is fairly short wavelength, typically 800-900nm - not THAT far from visible light.

Thermal IR that you might try to film is typically black body radiation from objects at 300K + up to say 900K, when the spectrum they emit starts to contain visible wavelengths. again.

Thermal IR from people is ~7000nm - a longway from our 800nm.

The semiconductor sensors used web cams and other digital image capture devices are quite sensitive to IR. As Re-design noted, there are filters built into the optical path to reduce the effect (and thereby increase the dominance of visible spectrum light). A classic technique for converting these devices into night-friendly cameras used by modders for the past several years is to remove that filter and provide an annular IR light source (a circlet of IR LEDS, for instance) around the camera for ir illumination of a target.

Camera sensors are sensitive to visible light and IR. But there are filters that filter out the IR light and let the visible light pass thru. But SOME ir light still gets thru but not enough to register on the sensor unless you are looking directly at the IR diode. Otherwise the the visible light is so strong that it overpowers the image of the ir image.

Shooting with IR film in a film camera works the same way.  If you don't us a very dark red filter then the visable light over powers the ir image and you get an almost normal photo.

You will find hot things looking "funny", but it tends to kick-in around red-heat, e.g. fires or stove-tops.

L

Whether automatic, or manually controlled, the cameras will have preset color temperatures set in them. If it's focused on/set to pick up a remote control, it can do so, but if it's set more to indoor/outdoor lighting it will ignore a certain set of values outside of that range and only show the pot (etc.) as you or I would see it. Cameras generally have three or four of these filters built in to match the conditions it will most often run across. Bonus reading found here.