In this instalment of our series, I'm going to be writing about infrared photography, film, and filters, with special attention to the so-called "x-ray vision effect." X-rays, of course, are a whole different thing: those frequencies are above UV, which is itself above the visible-light spectrum. Infrared (IR), on the other hand, lives below visible light. Below infrared, you find heat and radio waves.
Because infrared frequency numbers are quite huge, it has been found convenient to specify their wavelength instead. For example, the infrared filter that I recently bought passes a certain spectrum of IR wavelengths, but especially 850 nm (nanometers). I bought it for a specific purpose: to test the IR "x-ray vision effect," having learned in my research that that is the wavelength where the effect works best.
I did many tests with the new filter, testing various fabrics: cotton, polyester, nylon. rayon, spandex, and so on. Much to my surprise, all of these tests came out blank: no image. The reason, as I now know, is simple: the sensitivity of Rollei IR 400 film does not extend to 850 nm. Perhaps that is why my new filter is not among those listed by Rollei as recommended: B + W RG665 / 090 /091 /092 / Heliopan RG645 / RG695 / RG715 / Hoya 25A / Kodak Wratten 25 / 29 / 89B / Lee 25 / Rodenstock 25.
Now I assume that numbers such as 645, 695, and 715 represent nanometer (nm) numbers. For this special effect, the closer we can get to 850, the better. But the highest number recommended for this film is 715. I've seen a lot of filters advertised for 720 nm, which should be close enough, so I'll probably get one of those.
By the way, my new filter says "digital" right on it. The thing is, all photocells inherently have better IR sensitivity than any readily-available film (but in cameras, most are equipped with an IR-blocking filter). That is why the TTL exposure metering in my Canon AE-1 showed a usable amount of 850nm light, although the film itself was not sensitive to it.
So most of my 36 exposures of IR film showed no image, But all is not lost. Fortunately, I shot the last eight exposures with my old, tried and true (and recommended) Hoya 25A filter. I got eight perfect exposures.
Those eight exposures, having been shot at a less-than-ideal IR wavelength, showed little, if any, "x-ray vision effect." I had a feeling, though, that I might be able to bring out the effect a bit more by playing with contrast and brightness. And so it was. I was even able to determine the relative transparency to IR of various fabrics. Here are a few images, for the sake of illustration:
In general, I found Nylon to be best for the "x-ray vision" special effect. I am especially impressed because this Speedo (74% Nylon, 26% Spandex) also has a liner in the middle part, which is 86% Nylon and 14% Spandex. To the extent that it's transparent, it's transparent through two layers.
These baggy, loose-fitting shorts are 100% Nylon.
This black sarong is 100% Rayon.
I wondered whether the same effect might be achieved with a non-IR image, just by fiddling with the contrast and brightness. The photo below is digital, shot in ordinary, visible light:
This is the same Nylon sarong. Nope, no transparency.
The photo below was shot on film. Same sarong.
Nope, no transparency in ordinary, visible light, even with adjustments to contrast and brightness.
It will be interesting to see how a 720 nm filter and IR film works out.
(To be continued)
In the meantime, shoot film, if you can!
Text and images Copyright © 2022 by Donald C. Traxler aka Donald Jacobson Traxler.
