Infrared images with a Digital Camera

Cameras have always been a technological masterpiece, originally combining mechanical ingenuity and optical brilliance.  Electronics came gradually, first to operate exposure meters and automatic settings, until the advent of digital photography brought a quantum change and effectively turned the camera body to a small computer.  That change from a mechanical marvel to a computer allowed rapid technical development, from 1.3 megapixels in the first Kodak DCS 100 based on a Nikon F3 body to the 61 megapixels in the new Sony a7R IV.  Equally important, prices of these systems have shrunk from $20,000 for the early Kodak system to a “mere” $3,500 for the top of the line Sony.  Sadly, the rapid development and associated obsolescence we expect and accept with computers is still a shock when camera bodies change almost every other year. Which raises the question, what to do with an old camera body that has almost no monetary value?  One answer is to have them converted to record in a different part of the light spectrum. 

Digital sensors are naturally sensitive to light in the infrared region so most cameras have a filter to minimize infrared transmission.  In converted cameras, this filter is removed and replaced with a new filter that limits the light reaching the sensor to a specific wavelength.  Filters for different wavelengths produce different results.  Camera converters have different name-brands for the filters but the effects are:

  • 850nm: Good for a dedicated black and white IR. The camera produces bright whites and pronounced blacks. With a custom white balance, the image is close to pure black and white without any processing.
  • 720nm:  This is the standard IR filter. It allows some visible light for false color, and good contrast for black and white.
  • 665nm:  This has an effect between the 720nm and 590nm, producing more vibrant colors than the 720nm for pale yellow leaves and brighter blue skies.
  • 590nm: This filter lets more visible light in, producing the most vibrant colors. Leaves are golden yellow, and skies are bright blue. Black and white contrast is lower than the deeper IR filters.

I use a 665nm IR-filter and as the visible spectrum extends to about 700nm, the filter allows some of visible light to pass through to the final images. Because the closest humanly perceptible color to this particular IR-filter is red (≈ 620 – 740nm), the entire photo takes on a deep tint of reddish-burgundy. Properly adjusting the white balance to something ‘neutral’ shifts the red tint into more distinguished shades of blue and yellow. Converting these images to black and white gives the typical IR image turning green grass and tree foliage white and blue skies to black.

Another way to present IR images is to try to bring a sense of normalcy to the image by returning the sky to the blues we we expect.  This requires Channel Swapping – i.e. mapping what would normally be perceived as red to blue. The web is full of ways to do this depending on which photo-editing program you use.  I record my images as RAW files and use Lightroom to catalogue them and do most post-processing.  [As Lightroom becomes more powerful I only rarely find a need to use Photoshop.]  The sidebar gives details of how I swap the channels and duplicate the file allowing me to import both the original file and swapped channel for processing in Lightroom. The gallery shows some typical examples.

Photographers are always advised to capture their images during the “golden hours” around dawn and sunset or in diffused lighting – never under clear skies at noon when the light is bright and harsh.  Yet those clear bright blue skies (or skies with a few clouds) are full of infrared radiation and offer excellent conditions for infrared photography giving jet black skies in Black and White and deep blues when channels are swapped.  That bright light also gives more flexibility when choosing camera settings.  IR light focuses at a different point when it passes through the camera lens.  On many lenses, especially those from past years, there is an additional mark to allow the focus point to be changed for IR light.  Most conversions services also adjust the focus point as part of the package, but even so, I thought it prudent to stop-down the lens to f/8 or f/11 to achieve a deeper depth of focus. That was before I read this blog article that specifically addresses the impact of diffraction in the IR region.  According to the author, diffraction softness begins at much larger apertures in the IR spectrum than in the visible region.  So now, I will limit my IR photography to f/5.6 and f/8 – assuming that the corresponding shutter speed is appropriate.

I had my old Pentax K10D converted by Kolarivision ( several years ago.  Like most toys, it probably gets used less than I expected but that is a function of the operator and not the camera or the conversion.  Simply, not every subject makes a good IR image.  Still, I am happy to have the additional tool, and recommend it if you have an old camera sitting idle on a shelf.

Swapping the Red and Blue colour channels

The program, EXIFTOOL makes exchanging the red and blue channels easy. It is only necessary to change the numbers indicating the pattern of the Bayer colour filter in the RAW files produced by your camera. Then, any program that reads the RAW file and develops the image will automatically switch the channels. For my old Pentax the original Bayer pattern is RGGB (0112) so this little batch file makes the change to BGGR (2110) and writes the changed file and original files with different names. I then import both files into Lightroom for “development”. Just change this code to the Bayer pattern for your camera.

Note, I convert my files to DNG format in the camera. I haven’t tried this on original Pentax (PEF) files. Lightroom also initially displays the original thumbnail in the changed file but updates and stores a new thumbnail with the changed sequence when creating the previews. [P.S. don’t try it on JPG files – they have already been developed! ]

What the “batch file” does:
Assume the original files are in: C:\00Exif
Assume Exiftool program in: C:\Data_files\Software\Exiftool
You can place your files elsewhere and adjust the directory names accordingly.

The “batch file” – just like old-fashioned DOS
exiftool.exe -exif:cfapattern2=”2 1 1 0″ C:\00Exif -ext dng
cd \00Exif
rename .dng_original A_.DNG
/* Comment – All done . . wait for a keystroke */
That’ it

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