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.
Full spectrum photography in the daytime
Full spectrum photography is extremely sensitive to the lighting style. Different light sources contribute wildly different amounts of infrared light. We'll start with the sun.
At a first glance, for many typical subjects, a full spectrum photo taken at daytime looks like a much pinker version of a normal photo. The sun emits significant infrared radiation and (at least on my camera) that radiation is favoured by the red channel.
Here's Gastown at midday in full spectrum.
Vancouver's Gastown neighbourhood as seen by the full spectrum camera.
On its own, it doesn't look that remarkable. The buildings have a warm pink tone and a few plants look unrealistically red and yellow. The sky is still mostly blue.
Here's the same scene in visible light only:
Gastown in visible light, using the hot mirror filter applied to the same camera.
If I were extremely meticulous, I could lock the camera to a tripod, shoot a pair of raw images with and without the hot mirror filter, subtract one from the other and hope that nothing moved while I attempt to infer what the added infrared contribution looks like.
...Or I can just shoot it directly using a dedicated infrared lowpass filter. This is the invisible near infrared radiation that is being added to our visible light scene and being rendered as pink:
Gastown in infrared, using a 850 nm lowpass filter.
Perhaps the first thing to notice here is that the sky is very dark. The very same Rayleigh scattering that gives blue light a rough time for its shorter wavelength lets red and especially infrared right through. On a clear day, in infrared, you're seeing straight through the atmosphere and into space.
Because a clear sky scatters infrared so much less, sunlight also gets diffused less and acts more like a spotlight. Shadows behind solids become much darker and there's less ambient lighting coming from the sky.
Another thing to notice is that plant foliage is consistently very reflective in infrared. I'd love to know if there's an evolutionary reason for this. Perhaps being reflective in general prevents heating up and drying out, and the few colours they do absorb are the ones that are useful for photosynthesis and signalling.
Let's switch to a landscape.
Stanley Park and Grouse Mountain as seen from Kitsilano, in full spectrum.
At larger scales, the high infrared reflectivity of foliage turns entire forests pink and red when seen with an unfiltered full spectrum camera. Additionally, there is a crispness to large shadows that simply isn't there in visible light:
Stanley Park and Grouse Mountain in visible light only.
Near infrared is better at passing through atmospheric haze than visible light. For large scale landscapes, this means we get more detail and better definition from the added light.
Looking only in infrared, when combined with the dark sky and sun-spotlight phenomenon, the effect is outright spooky.
Stanley Park and Grouse Mountain in infrared light only.
In visible light, the contrast in the above scene is driven by the dark green of the forests and how much it has been obscured over the distance by haze. In infrared, the contrast is almost entirely due to hard shadows.
Of course, near infrared's ability to see through haze has limits. Clouds still look like clouds in near infrared, and this is because of Mie scattering where light is being deflected by water droplets much larger than the wavelength.
An old brick house and smoke stack shot (from left to right) in visible light, full spectrum, and infrared.
On partly cloudy days, the infrared reflectivity of clouds combined with the lack of light from a blue sky can add a surprising amount of contrast. And while the scattering behaviour of clouds is similar between visible and infrared, there are still cases where even an overcast sky looks wildly different in infared.
An overcast sky during sunset. The setting sun is behind the camera, below the clouds, and off to the right. Left is infrared, right is visible.
Generally, I find the only way to know what looks different is to simply point the camera at everything and compare its images to what I see until the ghosts are revealed.
Late last summer in Vancouver, we had a couple days of wildfire smoke that reduced visibility to the point where we couldn't see the local mountains from accross the city.
The view accross Vancouver on a smoky day, looking north towards the mountains and over downtown, shot in visible light.
I didn't take a full spectrum shot in this case, but I did take an infrared-only photo using the 850 nm lowpass filter. And there, once again, were the familiar local mountains, hazier than usual but still plainly visible.
The same smoky view accross Vancouver, shot in near infrared.
We've seen now how from afar, landscapes and especially trees look especially crisp and bright in full spectrum and in infrared. Up close however, it's a bit of a different story. Let's move to another clear and sunny day and visit the woods.
An old mossy red alder, covered in ferns and surrounded by western red cedars. Shot in full spectrum.
Curiously, when looking at foliage up close, it becomes clear that leaves are not only more reflective but also much more translucent in infrared than in visible light. Foliage looks brighter, but that brightness gets transmitted through and scattered everywhere. So when surrounded by trees on a sunny day, there's actually a net increase in ambient lighting and a loss of the crisp shadows that we see at landscape scales.
The same old mossy alder, shot in visible light only.
Blackberry bushes in full spectrum. Infrared everywhere.
Blackberry bushes in visible light only. Visible light is absorbed more strongly by foliage, leading to harder shadows up close.
Full spectrum photography at sunset
Golden hour is a special time for infrared. The setting sun's warm sideways glow is full of infrared while the ambient visible light starts to fade. Many of the effects of full spectrum photography become exaggerated during this special window of time.
Trees at Camosun Bog during sunset shot in (left to right) visible, full spectrum, and infrared.
Cathedral Mountain at sunset in visible light, as seen from Jericho Beach. Some warm sideways light is visibly casting a shadow over the valley, but there is significant haze.
Cathedral Mountain at sunset in full spectrum. Everything is pink, and the enormous shadows of the mountains are more vivid.
Cathedral Mountain at sunset in infrared. The valley is cast into complete darkness.
Whenever shooting a subject with a mixture of visible and infrared light, it becomes readily apparent that infrared light focuses differently from visible light. For many subjects, this can mean having to choose between crisp visible contours and an odd pink glow, or blurred edges with some unusual pink features inside. Some things never look sharp no matter where you move the focus.
Trying and failing to get all of Cathedral Mountain in focus.
Other details from the same four shots. Would you rather look at the trees or at the buildings?
This tanker ship was reflecting large amounts of both visible and infrared light and consequently looked bad at any focus.
If this ever becomes an issue for you, the workaround is to lower the aperture and consequently increase the exposure and/or ISO, producing an image that's crisper everywhere at the loss of depth of field.
Personally, I'm rather fond of the ability of this technique to put pink trees in focus while human-made buildings are blurred away.
Full spectrum photography at night
As soon as the sun sets, we can appreciate different light sources in isolation and see how varied they are in terms of how much additional infrared they emit.
My city is in the middle of phasing out sodium vapour street lamps in favour of newer LED lamps. While sodium vapour lamps are known for that characteristic yellow spectral peak, it turns out these lamps also have a big peak in the near infrared range.
A dead-end street lit by a sodium vapour lamp, shot in visible light.
The same shot in full spectrum.
When shooting in full spectrum, this means the nighttime city is a patchwork of pink hotspots. Here's an intersection half lit by LED and half lit by sodium vapour:
A street intersection shot in full spectrum. The foreground is lit by an LED street lamp while the background is lit by sodium vapour lamps.
The same intersection in visible light. The cotton candy pink of the surrounding foliage returns to the familiar dim yellow.
Incandescent lights appear very similar and extremely pink due to their long tail of additional infrared light.
Perhaps more surprising at night time is the fact that we're surrounded by lights that are only visible in infrared. Take this house for example.
A house in the suburbs with LED christmas lights, shot in visible light. Ok, I admit there are some hints to be seen here but that's because my IR-blocking filter isn't perfect. To the eye, there's nothing unusual to see here.
There are three separate security cameras here, each of them shining brightly in near infrared. You know that style of black-and-white night-time security camera footage, i.e. "night vision?" It's all near infrared. A full spectrum camera is a security camera detector. And there are a lot of security cameras even in this quiet neighbourhood.
The same house in full spectrum.
One area I have not explored is night-time astrophotography. There's a community of astrophotographers who use full-spectrum-modded cameras for the improved exposure, and some even use special-purpose filters that block specific types of atmospheric haze and human-made light pollution in order to get clearer images of the night sky.
Full spectrum photography indoors
Moving inside, without sunlight streaming in, we can see what some other artificial light sources look like on their own.
Let's start with something that wouldn't even be considered a light source: my stove! Here's my electric stove turned on in the dark in visible light:
My stovetop at night in visible light.
If my eyes could see infrared the same way the camera does, the stove's light would be enough to read by.
My stovetop at night in full spectrum.
Another strong infared emitter you're likely to come accross indoors is halogen lights. The ones in my place seem to put out more infrared than visible light, and it does weird things to colours.
A kitchen still life, light by halogen lights and photographed at night in full spectrum.
The same still life during the day and lit only by ambient sunlight, also in full spectrum.
By comparison, more modern LED lights emit virtually no infrared light at all. My local grocery store is lit entirely by white LED lights, and as a result, full spectrum photos there look indistinguishable from visible-only photos.
Fruits on display at my local grocery store in LED lighting, shot in full spectrum.
As human-made lighting gradually becomes predominantly LED-based, more and more human spaces look predictably boring in full spectrum. On the positive side, we're saving energy and I am reminded to go outside to find more interesting things.
Closing Remarks
There are many more oddities to share but this post is getting long enough.
I've covered how full-spectrum photographs look when the entire extended spectrum of visible and infrared (and ultraviolet) light enters the camera all at once, and I've also shown what the infrared contributions look like in isolation.
Next up, I'll be exploring what full spectrum photography looks like through selective filters that isolate or remove just a few colours at a time. We'll get into some serious spectral arithmetic and we'll see trees in any colour you please and visit some surreal places. Maybe if I find a brave subject, there will be some portrait photography as well.
Once the weather warms up, I'll be sharing my findings from pure ultraviolet photography as well.
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