Creating "False-Colour" Infrared Images Using Nikon D1
By Bjørn Rørslett
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All images: © Bjørn Rørslett/NN
Taken in May, 2000 using 35 mm f/2.8 PC-Nikkor lens on a D1, with stacked polarizers (see text)
A: Maximal polarization
B: Intermediate polarization
Sometimes you are in for really big surprises. I've experimented with stacking polarizers several times before, and obtained some strange effects with film-based systems. However, when I tried this trick with my D1, I unexpectedly got images that closely resemble those of false-colour infrared film. The pale spring sky turned into a deep blue, and the fresh foliage became vibrantly red. Since I obtained the first shots, shown above, I have verified that this is indeed an infrared image. If I add a Tiffen hot-mirror filter (which blocks IR) to the stack of polarizers, the colour rendition of the digital image turns into the ordinary again. However, besides involving IR, the "false-colour" images have an additional UV component. This is readily apparent when using the UV-Nikkor 105 mm f/4.5 to record "false-colour" images: I tested this using dandelions, which have a distinct UV patterns in their flowers, and sure enough, this familiar pattern emerged. When the usual Micro-Nikkor 105 mm f/4 was substituted for the UV-Nikkor, the UV floral pattern disappeared. I'm going to publish such pictures when I'm entirely familiar with this novel technique.
I knew in advance that Nikon D1 could capture UV as well as IR radiation, and already had the images to prove this. However, why I got the stunning "false-colour" IR effect is quite unclear to me. That doesn't matter much because it's obvious that interesting pictures can be obtained. So be it.
Then, how is this effect obtained, besides just using a D1. Really it is simplicity itself. You just need to stack two polarizers atop each other. At least one of these should be the linear type, preferably both. Also, experiments show that combining high- and low-quality filters give the best results. For my usual setup, I attach a B+W 60 mm thread filter onto an old Nikon 52 mm polarizer (this filter has outer thread size of 60 mm so mates happily with the B+W). In the beginning, with F5 and Arca-Swiss cameras, I used a Hakuba filter instead of the Nikon to get even more stunning results. Unfortunately, for some non-explicable reason I gave my poorly-performing Hakuba filter away before it could be tried in the digital era. When the filters are rotated independently, you'll notice strong attenuation of light and sectors of irregular colours will appear. Adjust the polarizers for a maximum effect and take the picture. Be aware that using a linear polarizer will throw off the meter on D1, so some experimentation is called for. Because exposures can be checked using the LCD display on D1, this is in fact quite easy. Make sure you also try different degrees of polarization, as this will impact the colour rendition by a significant degree.
Please note that due to the thickness of the filter stack, focal lengths shorter than 35 mm will show vignetting of the image even on the D1.
For more information on the Nikon D1 camera and its performance under field condtions, my review pages for it should be consulted.
Last Update 1 October, 2002