Sigma SD1 and SD15 for Digital Infrared Photography

Infrared photography involves capturing light at wavelengths beyond the visible spectrum. Infrared energy is reflected quite differently than we are accustomed to by many organic and inorganic surfaces, and the results of landscapes bathed in infrared light has long been a favorite style of photography for fine art photographers since the silver halide days of centuries past. A unique design advantage of Sigma’s DSLRs allows creative photographers to quickly and easily swap between visible spectrum and infrared photography.

Lilypads, trees, and clouds are highly reflective in Infrared wavelengths, as this scene from midday in Spring Lake, NJ, illustrates. Camera: Sigma SD1 with IR blocking filter removed. Lens: 10-20mm F4-5.6 EX DC HSM Infrared Filter: Cokin P 007 (89B) Infrared passing filter (50% transmission at 720nm) | Exposure: 1/80 at F/13.0 ISO 100 X3F Raw Capture. Converted through Sigma Photo Pro 5 to monochrome.

All digital SLR sensors are sensitive to infrared wavelengths–but these wavelengths beyond the visible spectrum are prohibited from reaching the sensor by IR-blocking filters. In the Sigma SD1 and SD15 Digital SLR cameras, the Infrared blocking filter is just inside the lens mount–and above the reflex mirror. It easily pops out to enable sensor cleaning, and this also allows energy of infrared wavelengths to hit the sensor.

And here’s the Lighthouse at Sandy Hook, captured in Infrared | Camera: Sigma SD1 with IR blocking filter removed. Lens: Sigma 17-50mm F2.8 EX DC OS HSM. Infrared Filter: Cokin 89B Infrared passing filter (50% transmission at 720nm). Exposure 1/400 at F7.1 ISO 200 X3F Raw capture. Converted through Sigma Photo Pro 5 to monochrome.

To create the dramatic, monochrome, infrared-only compositions as shown here, an Infrared passing filter is then placed in front of the lens. The IR-passing filter blocks the visible spectrum, so only energy in the infrared wavelength (720 nanometers, in these examples) is captured on the sensor and recorded in the X3F RAW file. Sigma Photo Pro 5 then converts the red-tinted X3F RAW files to professional quality monochrome TIFFs.

The infrared-blocking filter on the Sigma SD1 and SD15 Digital SLRs sits in front of the reflex mirror, and must be removed to clean the sensor. A gentle push upwards at the arrow and the Sigma SLR sensors are receptive to both visible spectrum light, and infrared energy beyond normal human vision.

The Sigma SD1 and SD15 are the only consumer DSLRs that are hot-swappable between visible spectrum and Infrared capture. In other digital SLRs, the IR-blocking filter is behind the reflex mirror, and is not removable without disassembling the camera. True, some aftermarket companies offer conversions to Infrared capture, but this process almost invariably voids the OEM warranty, and is definitely not quickly and easily user-reversible while on location.

An infrared passing filter is then placed in front of the lens to isolate infrared wavelengths and exclude visible light. The Cokin P 007 (89B) filter shown here and used for the photos in this article has 50% transmission at 720 nanometers.

Here’s a quick rundown of my Infrared workflow with the Sigma SD1

Infrared Photography works best when the sun is bright, and there are a lot of elements in the frame that will dramatically reflect infrared wavelengths, such as sunlit trees, lawns, other foliage, and clouds.

The scene should be framed through the viewfinder, without the front-of-lens Infrared passing filter installed. Once the scene is framed, the Infrared passing filter can be placed in front of the lens. At this point, you can adjust your autofocus, as AF operates with the IR light passing through the filter. In any event, it is wise to stop down to a smaller aperture to build in some extra depth of field. Once the camera is set up, I take some test exposures and review the image preview and histogram and make any necessary adjustments. Auto Exposure Bracketing is a huge help here. And of course I’m shooting in X3F Raw here.

Metering in infrared can best be described as guess work. But Auto Exposure Bracketing helps to quickly fine-tune the exposures. I look for good rich shadow tones, and an overall red-tinted image. If it’s mostly pink, or there’s areas of yellows and whites on the LCD screen, the exposure was too long. In this series of images bracket at 2.7 EV intervals, the far left image has the best exposure.
Click on the Adjustments button in Sigma Photo Pro 5 and select “Monochrome” from the White Balance dropdown, and in an instant, the red tint of the infrared filter disappears, and a classic high-contrast silvertone image appears in its place.
Some quick adjustments to shadows, highlights, fill light, and contrast really make the image pop. And if desired, a tint can be added to the image using the color adjustment wheel. From there, it’s a simple matter of clicking “Save As” and exporting a high-resolution, 16-bit TIFF for final web or print optimization in Photoshop or Lightroom.

Do you have any more questions on Infrared Photography with the Sigma SLRs? Drop Jack an email!

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