In our latest episode I include a few infrared photographs. I suspect many of you will not be familiar with infrared photography, so I’ll give you a little overview. At the bottom of this post is a link to my photography website where I’ve published a post that goes into a lot more detail.
Your camera’s sensor and Bayer filter
A normal digital camera has a special filter in front of its sensor called a hot mirror or infrared-cut filter, which blocks infrared light (like 720nm wavelengths) so the camera only sees visible light—what our eyes see. The sensor itself is naturally sensitive to a wider range of light, including infrared, but the filter is there to prevent infrared from distorting color photos. Additionally, each pixel on the sensor has a tiny RGB color filter (called a Bayer filter) that splits light into red, green, or blue, allowing the camera to build a full-color image by combining them.
It is possible, however, to capture the infrared. To convert a camera to 720nm infrared, a technician carefully removes the infrared-cut filter from inside the camera, exposing the full light sensitivity of the sensor. (I got my Sony A7R converted by Alan at Infrared Camera Conversions. Check out his website for an exhaustive gallery of IR photography.) Then, they install a 720nm infrared filter in its place. These days it is done over the sensor, which is permanent, but it can be done by placing a filter over the lens (this is how it was done in film days but it massively affects exposure time). This filter blocks most visible light and only lets in infrared light above 720nm. The camera can now “see” in infrared, but because the Bayer filter is still there, the sensor still divides the light into RGB channels—just using infrared instead of visible colors. This means infrared images still have color information, though it’s not “true” color.
What does 720nm mean?
Different infrared wavelengths, measured in nanometers (nm), affect how much visible light is blocked and how the final image looks. Lower IR wavelengths like 590nm or 665nm allow more visible red, orange, and yellow light through, producing colorful “false color” images with surreal skies and foliage effects. This is quite a common conversion and you’ve probably seen examples without realising it. As you move higher, 720nm blocks most visible light except deep red, giving more muted colors and stronger infrared contrast. This is ideal for classic IR photography but it’s the one I use for black and white photography because, although 850nm and above block nearly all visible light, resulting in pure black-and-white images with high contrast and deep shadows, the higher the nm, the less visible light is captured. This can make images look more ghostly or ethereal.
General Effects
One of the significant effects of IR photography is how it changes foliage. Foliage looks white in infrared photography because leaves strongly reflect infrared light, especially around 720nm, making them appear very bright or white to the camera. As a rule, I tend not to use IR photography if the subject includes trees or grass, although I include them here as examples.
The one effect I DO like is how 720nm renders the sky and water. On a cloudless day the sky will look dark, black even, and the same happens with water. This makes IR photography ideal for bright, sunny and cloudless days. It’s one reason why I got my Sony A7R converted to IR: midday is not a great time of day to be taking normal RGB photos, but it lends itself perfectly for IR photography.
As you saw in the first example photo, the camera is capturing the real infrared signal, which renders the image with pink hues. Using Adobe Camera Raw, I then convert to black and white and then set to with the contrast, black and shadows sliders to bring in more contrast.
Where 720nm infrared shines though is when foliage is avoided altogether. It can produce some great contrasts akin to black and white photography. It’s also worth noting that you can set your camera’s custom white balance to display in IR in both the EVF (view finder) and on the screen. This helps you ‘see’ the world in black and white when composing an exposure.
If you are interested in reading more about infrared photography, I’ve written a post on my photography website where I go into more detail and give loads more examples of the results you can achieve. Check it out here.
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