Shooting IR with a Full-Spectrum Modified DSLR

With a Full-Spectrum modified DSLR, the world of IR photography is opened up to you.  These infrared wavelengths are normally invisible to your eyes, but when made visible with a modified camera and an IR filter, they convey the world in a much different fashion.  IR photography is traditionally captured through a filter that allows ONLY IR light, or possibly IR light and some portion of the visible spectrum to pass through to the camera's sensor.  A true IR filter will appear virtually black to the naked eye and nothing can be seen through it.  With a DSLR that has been modified to be sensitive to the widest segment of the spectrum possible, we will shoot IR by placing either a lens mounted IR filter or a clip-in IR filter in the light path to block all wavelengths shorter than the specified cutoff wavelength of the filter.  For instance a filter labeled as 720 nm will block all wavelengths shorter than 720 nanometers and pass wavelengths longer than 720 nanometers.  Since the human eye is blind to IR light, the optical viewfinder will be useless in composing your subject.  However, the camera's sensor is very sensitive to IR with a full-spectrum modification and you can use the Live-View feature in the later model Canon DSLR's to see your subject on the LCD screen in real time.  If you don't have Live-View, you can simply shoot a test image and adjust composition from the review image on the LCD screen.  Autofocus works fine and results in crisp focus as in normal photography.  Since we are using lenses that are corrected for normal wavelengths but not for IR, and we are capturing a fairly wide range of IR wavelengths, it is helpful to use a fairly high f-stop to get a good focus depth of field.  Even though the IR filter is almost opaque to visible light and you might think long exposures would be required, the full-spectrum modified camera is quite sensitive to IR and short handheld exposures are fine.  The DSLR sensor has a Bayer matrix of red, green or blue filters covering each pixel and you may expect that infrared light would only be captured by red pixels.  However, even though the red pixels are very sensitive, there is a significant response to IR light in the green and blue pixels as well since their Bayer filters are somewhat transparent to IR light.  Some IR photographers will use only the data from the red channel in their final monochrome images.  However, don't overlook the data in the green and blue channels.  Often the most detail will appear in the green channel.  Also, if you want to experiment with pseudo-color images, such as those below, you will need to be careful not to overexpose any of the three channels.  Thus, it is helpful to set your camera's display screen to show an RGB histogram so that you can adjust the exposure to prevent clipping any channel's data.

Here are some examples of IR photography with a Full-Spectrum modified camera from Eric Chesak -

The images below were captured with a Full-Spectrum modified Canon 40D along with a Massa 720 nm IR lens mounted filter.  All were set for manual mode, f/13 and 1/340th of a second exposure.  I used the red/blue channel swap technique described on many IR photography processing web sites to create a blue sky.




In the following example, the same camera and filter were used, but only the data from the red channel used to create a monochrome image.