Canon Digital Rebel (300D) Modification - PAGE 13

Infrared Sensitivity Comparison

by Gary Honis

This is Page 13 of Part 1 of a Two Part Guide:

Part 1: Removal of IR Cut Filter for Astrophotography & Infrared Imaging

Part 2: Plans for Peltier Cooling

Best viewed at 1024X768 resolution

Infrared Sensitivity Comparison:

How sensitive to infrared is the Digital Rebel after the Canon IR Cut Filter is removed? Can similar infrared results be obtained by using the Rebel unmodified with an infrared lens mounted filter, such as the popular "Hoya R72". For a comparison, I used an unmodified Canon 10D with a HOYA R72 filter and the modified Digital Rebel (IR Cut filter removed) with a HOYA R72 filter to image the infrared light from a TV remote control unit. The same camera lens was used for all images. The focus was not changed when swapping cameras on a fixed tripod. All images were taken at ISO 400 and F 5.6.

Modified Rebel - TV remote control unit imaged with no HOYA R72 filter - 1/20 second exposure:

In the above image all wavelengths of light are reaching the CMOS imaging chip, both visible and infrared light.

The following four images were taken using the HOYA R72 infrared filter to filter out visible light and pass mostly infrared light:

1. Modified Digital Rebel without HOYA R72 filter:

Exposure: 1/125 second

2. Modified Digital Rebel with HOYA R72 filter:

Exposure: 1/125 second

3. Canon 10D with HOYA R72 filter:

Exposure: 1/125 second

4. Canon 10D with HOYA R72 filter:

Exposure: 10 seconds

To obtain an infrared image with the Canon 10D that was as bright as the infrared image with the modified Digital Rebel (Image #2 above), an exposure length of about 10 seconds was needed (Image #4 above). Images #2 and #3 above can be compared to show the difference in sensitivity with removal of Canon's original IR Cut filter. This assumes that the IR Cut filter used by Canon in the Digital Rebel (300D) and 10D are similar.

The spectral response curves below show how little infrared light the Canon IR cut filter (red curve in diagram) allows to be passed to the CMOS imaging chip, which is very little above 700nm:

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

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Infrared Imaging - Infrared Filters - Canon Digital Rebel Camera