Daytime Infrared Hoya R72 Filter:
A popular filter for infrared imaging is the "Hoya R72". Since the modified Rebel has its Canon IR Cut filter replaced with a coated clear glass window, the CMOS imaging chip is receptive to all wavelengths of light. The visible light range is from 400 nm (violet) to 700 nm (red). Wavelengths above 700 nm and up to about 5000 nm are known as near infrared. Here is the transmittance curves showing the Original Canon IR Cut filter(that has been removed), the X-Nite CC1 color correcting filter and the Hoya R72 infrared filter:
Adding the Hoya R72 infrared filter to the lens, without using the CC1 filter, allows only wavelengths of light above 700nm to be imaged (shaded blue above) and blocks all others. In the ice storm photo below, an X-Nite CC1 color correcting filter was used for the normal image and the Hoya R72 filter was used in its place for the infrared image. Focusing through the camera's viewfinder when using the R72 filter is not possible because it is a very dark red, nearly black, filter. The camera was tripod mounted and focused with the CC1 filter; then the CC1 was removed and replaced with the Hoya R72 being careful not to change focus of the lens. The camera lens then needs to be "short focused" a little to achieve focus with infrared light. The focus point of the lens in infrared is found by trial and error unless the lens has "red" focus shift markings for infrared.
Normal versus Hoya R72 Ice Storm Image:
The following image is a "mouseover image". You will need to have scripting allowing in your web browser for this to work. Move your mouse cursor over the image and you will see the infrared image of the same scene. Move the mouse cursor off the image to go back to the normal image:
Move cursor on and off image:
In the above photo, imaging in infrared resulted in vegetation such as the pine trees appearing bright (white). The atmospheric haze is also removed as infrared cuts right through it to reveal mountain details and a distant mountain range. Ice loading on the tree branches also appears thicker.
Normal versus Hoya R72 Indoor Plants:
In the above photo, imaging in infrared resulted in plant leaves glowing very brightly.
To learn more about Infrared Imaging with a Digital Camera, see the Digital Photography For What It's Worth article: Infrared (IR) Basics for Digital Photographers—Capturing the Unseen
Continue to Page 13: Infrared Sensitivity Comparison