My friend Brian is a consummate photographic magician with a lifelong passion for making award-winning pictures. His generosity recently enabled me to pick up a fascinating facet of photography from where I'd parked it several years ago, when specalist films and darkroom techniques were the only affordable, practical way for amateur photographers to peep into the world of infra-red imaging.
The Latin word "infra" means "below". Infra-red light (IR) is a term which describes a certain kind of radiant energy having longer wavelengths than visible light. Practically all of our IR comes from the sun. IR is invisible to the human eye. If you could see past one end of the rainbow, just below the colour we call "red", then you'd see the world differently, probably as some insects do.
We humans can only feel IR as warmth on our foreheads. Some cameras can "see" infra-red light. If you look at the business end of your TV remote, it's unlikely you'll see anything flashing when you press a button, even though it is emitting IR light signals. But if you then view the same thing happening using your phone's camera, you'll likely see some very bright flashing. This trick is actually a quick way to check that the remote's batteries are good.
There are specialist companies who can modify an ordinary DSLR1 camera, converting the internal light sensor system to respond almost entirely to infra-red light. Advanced Camera Services did a great job for me on the Nikon D50 which my aforementioned friend bought me for my 60th birthday this month. ACS install only the steepest, flattest filtering possible, thereby blocking all visible light. I chose the option to record at 720nm, which is the way physicists measure the wavelength of light2. This highly accurate, objectively proven filtering specification is precisely what gives these photographs their characteristic "look".
The picture here is actually an Infra-red "false colour" image, because the artificially blue sky effect was added later by Brian, using a combination of Adobe Lightroom and Photoshop editing techniques. My little old slow laptop simply isn't up to the job!
This tree grows on the side of the hill near Kendal Castle. The chlorophyll in the sunlit green leaves and grass (as we see them) creates lighter tones because it reflects lots of IR . If you look at the dark shadows, where there's far less IR, you'll understand why we sometimes appreciate the shade of a big leafy tree.
1. Digital Single Lens Reflex
2. If you could cut a one meter ruler into one billion pieces, each piece would measure one nanometer in length (1nm). If the IR light in my camera was like miniscule waves on a microscopic ocean, each peak of water would be 720 nanometers apart from its immediate neighbour.