GoKawiilFull Spectrum and Infrared Photography
This blog post picks up where my earlier post, DIY full-spectrum mod on an old DSLR, left off. If you want to know how I obtained this weird camera, go read that first!
Quick refresher
A full-spectrum digital camera is an ordinary camera except with its manufacturer-installed UV- and IR-blocking filters removed. This leaves the camera with a bare image sensor that picks up extra wavelengths beyond what the human eye can see. Without any extra filtering, these extra wavelengths show up as additional light contributions accross colour channels, depending on the lighting source and the camera sensor's colour filter array pigments.
Methods used
For all photos in this post, I am using my full-spectrum-modded Canon EOS Rebel T6 DSLR, and a very basic lens. To simulate a normal camera, I am using a "hot mirror" lens filter, so-called because it reflects "hot" infrared light away from the camera, restoring its usual visible-only sensitivity. For fully infrared shots, I am using a 850nm lowpass filter which blocks all visible light, letting only near-IR and longer through. Both filters were purchased from Kolari.
From right to left: full-spectrum-modded DSLR camera, "hot mirror" infrared-blocking filter, and 850 nm infrared lowpass filter. The hot mirror looks faintly cyan to the eye but camera white balances compensate for this. The infrared lowpass filter looks fully opaque because it does not allow any visible light to pass through.
It's worth noting that when I refer to infrared here, I'm referring specifically to near infrared, with wavelengths of around 1000 to 850 nanometres. This is much shorter than thermal infrared and only slightly longer than visible light, and is distinct from thermal imaging. Optically, it behaves largely very similarly to visible light with some key differences in how specific materials and media reflect and scatter.
I will not be adjusting the white balance in any full spectrum shots in this post. This is largely a stylistic choice. Calibrating the white balance for a scene with plenty of infrared light tends to desaturate colours quite heavily. I prefer warm pink highlights over everything looking dull.
I will also be speaking very little about ultraviolet here. While it's technically more sensitive than before, the amount of ultraviolet light that manages to make it into my camera is tiny compared to the levels of visible and infrared light, and so it typically plays a negligible role. In a future blog post, I will give ultraviolet light the special attention it deserves.
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