Photos

Recently, I had the opportunity to tour Le Four à Chaux, one of the larger fortifications on the Maginot Line. Le Four à Chaux is an underground artillery battery and observation point, basically -- a complex tunnel warren, like what Ho Chi Minh would have done in Vietnam if he had enough money and concrete. We spent a couple of hours touring through the tunnels and rooms.

Overall, it was a great experience. This tank is a nice touch to the outside of the museum, though a bit incongruous -- it's an American tank, not French, and according to our guide, it's Korean War-vintage. But hey, it looks like it belongs there.

Regarding the technique, this is a digital infrared photo, one of the first shots from the field using my newly converted Digital Rebel XT. The false colors are obtained by using the custom white balance function, which was calibrated by the company that converted my camera, LDP.

In previous photos, such as this Budapest statue photo, I took digital IR photos using a regular DSLR and an IR filter. However, this technique was limited.

DSLRs are engineered to best expose photos in the visual light spectrum, or light between the wavelengths of around 380-750 nanometers (nm). Manufacturers therefore install a "hot mirror" to block out most ultraviolet light and infrared light. Not all UV and IR light is blocked, though. So, using an infrared filter, such as a Hoya R72 (which blocks out light below 720 nm), regular DSLRs can be used to take near-IR photos. However, because the hot mirror and the UV filter are working against each other, very little light gets to the camera, requiring very long exposures (usually 10 seconds at f/8, ISO 100). Also, because the IR filters are nearly or totally opaque to our eyes, you can't compose and focus with the filter on, and you normally have to use a tripod. Finally, because lenses aren't designed with IR shooting in mind, the images can suffer from "hot spots" in the center of the image.

Enter IR conversion. There are several companies out there that are happy to convert your DSLR to IR-only -- that is, they will remove the hot mirror from your sensor and will replace it with an IR filter. Because it's behind the lens and not in front of it, you can now shoot on the fly.

It's not the cheap and easy solution. But having taken my converted camera into the field, I am finding huge possibilities for photos I'd never have gotten before.