Beyond the Rainbow: IR Photography

You’ll need plenty of sunshine and that’s why summer is the best time to get into IR photography.

Unfortunately IR from sunlight will be filtered out once you take your camera underwater though you might get some interesting results when experimenting with a flash. But our topic this time is mostly for your photography in daylight.

In the days of film there were IR sensitive films on the market, but they were also heat sensitive and generally not a pleasure to work with. Secondly, you had to have an IR filter on your lens which is basically black, letting no visible light through – not very helpful on an SLR. However, digital photography has changed all that.
IR photography relies on IR radiation reflected back from objects so to begin let’s look at the spectrum of visible and IR light.

The visible light spectrum extends from around 400 to 700 nm (nanometers), but sun light stretches well beyond both these limits. IR comes after the red end of the rainbow. The photographically interesting near IR region extends from 700 to around 1200 nm. Further down the line you get the far IR, which is heat.
IR photography is not simply an extension of the visible light region. Visible light is deliberately blocked out and IR filters have a certain cut-off between 650 and 850 nm. The camera captures only the IR reflected off whatever is in front of your lens. Blue sky turns dark simply because it doesn’t reflect any IR.

What stands out most in IR photos is bright foliage. It often looks like a winter landscape. This strong reflection from green vegetation is called the “Wood Effect” (after the IR photography pioneer Robert Wood, around 1910). There is a small contribution to it from chlorophyll fluorescence, but that is marginal and not the real cause of the brightness of the vegetation.

Digital IR photography

In contrast to photographic film, all image sensors are sensitive to IR and have been used, for example, in security cameras long before they got into our cameras. In fact, IR needs to be blocked out for normal photography. If you wanted to be absolutely certain of losing any guarantee on your camera you might try and replace the built in IR-block filter in front of its sensor with a suitable IR filter (which blocks out visible light). This is not for the faint of heart, and it makes the camera useless for conventional photography.
To explore the world in IR we have two options. You can use your existing camera and put an IR filter in front of the lens. There are different types available that cut off visible light below around 660, 710 or 850 nm. Cutting out the visible light is a fancy way of saying that these filters are black! Because of the built-in IR block filter, only a trickle of IR is going to get through to the sensor. A tripod is essential and you need to compose your image, then put the filter on, refocus (because IR focuses differently to shorter wavelengths), and then work out the exposure. Expect exposure times ranging from several seconds into minutes.

The other option is to get a dedicated IR camera, assuming you didn’t go for the DIY job!.

Choosing a camera and filter

There are a number of companies that offer to convert one of your existing cameras into a dedicated IR shooter, or they will modify a brand new one for you. I chose Kolari Vision (kolarivision.com) and can highly recommend them.
Point-and-shoot cameras are a great option for getting started on IR photography as they are small and light and don’t give you a hard time with focussing and exposure. On the Kolari website you’ll find lots of information about choosing the right camera.

Next you need to select an IR filter which will be fitted in front of the sensor. The 720 nm is the standard classic IR filter. If you want a bit more colour coming through you can opt for 590 or 665 nm. Then there is the 850 nm deep IR filter for the hard-core IR addict, which is only suited for B&W work.

Shooting in IR and post processing

If you opted for a simple point-and-shoot camera you’re ready to go. The camera will set the right focus and exposure for you. With DSLRs you need to watch out for focus correction and exposure compensation.  
Don’t wait for the evening light. IR photography is best done in mid-day under full sunshine! White balance is a nuisance - the experts recommend setting the custom white balance by pointing the camera at a batch of grass. Most IR photos are viewed as B&W images and if you opted for the classic 720 or 850 nm IR filters you’ll get B&W images anyway. They might be a bit dull-looking, but that is easy to fix by simply pushing the contrast.

For my camera conversion I opted for the 665 nm filter which lets a bit of visible light through, and gives some colour information. Now we’ll look at colour but if you want to turn your shots into classic B&W images, you need to convert them to B&W and increase the contrast.

IR photography is full of surprises. A blue shirt might come out light or dark, depending on the material. A good example is my camera bag: it is black, but turned white in the IR shot. This makes sense, because the manufacturer used a material which reflects IR to keep the contents cool.

If you choose the 665 nm filter for your conversion (and even more so, the 590 nm filter), you’ll have plenty of colour to play around with. When opening the shot everything looks dull and pinkish. To get a blue sky you need to swap the red and blue colour channels. This is best done with the Channel Mixer which you’ll find in any image editor. The Kolari Vision website has a tutorial on how to use the free Gimp editor.

If you use Photoshop, go to Image > Adjustments > Colour Mixer. Select the Red channel, reduce the red to 0 and set the blue to 100 (Image 3). Then do the same for the Blue channel, reducing blue to 0 and pulling the red up to 100.  

This will give you a blue sky which you can selectively target with the Hue/Saturation tools. Leaves and grass take on a yellowish hue, which you can also perfect to your taste, or you might prefer the white leaves in Image 4 by desaturating the yellow in the leaves.

If you have an older point-and-shoot camera lying around, why not convert it to IR? IR photography is fun, full of surprises and will greatly enhance your creativity.