Sigma SD1 and SD15 for Digital Infrared Photography, By Jack Howard

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.

[caption id="attachment_7363" align="aligncenter" width="604" caption="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."][/caption]

 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.

[caption id="attachment_7366" align="aligncenter" width="604" caption="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."][/caption]

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.

[caption id="attachment_7367" align="aligncenter" width="604" caption="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."][/caption]

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.