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Tuesday, January 26, 2010

Trying Infrared

Infrared, Inside Out • From CRT To LCD, And Even LED • 2X Or Not 2X • Separate The Pros From The Cons

Labels: How-ToColumnTech Tips

Ferns in the mountains of Molokai, Hawaii, taken with a Canon EOS-1Ds internally converted to IR photography and a 24mm Tilt/Shift lens set to ƒ/16 and 1/45 sec. with ISO 200. The image was optimized in Photoshop.

Infrared, Inside Out
Q What are the advantages, if any, of having a digital camera converted solely to infrared capture versus using the B+W 093 IR filter on my DSLR?
G. Gould
Via the Internet

A All digital cameras are extremely sensitive to infrared (IR) light, and since 2002 the manufacturers of digital cameras have placed an IR cut-off filter (sometimes referred to as a hot-mirror filter) in front of the sensor to minimize the amount of infrared light that reaches it; infrared affects the color rendition, so manufacturers want to eliminate it.

The IR cut-off filter improves the sensor’s visible-light imaging performance. Both DSLRs and compact digital cameras, therefore, severely restrict the amount of infrared light that hits the sensor. So you have three options for shooting IR with a digital camera: adding an IR filter over the lens, replacing the cut-off filter with a clear filter or replacing the cut-off filter with an IR filter. The latter two options require special intervention by a professional; don’t try this at home.

There are several external IR filters available at varying intensities: the Hoya R72, the B+W Digital Pro Infrared #093, the Singh-Ray I-Ray infrared filter and the Wratten Gelatin IR filters, among others. Achieving a significant IR effect with a filter over the lens of an unmodified digital camera requires a very long exposure, with all the negative effects that brings: subject movement and camera movement are emphasized. The exposure will vary among camera models, depending upon the sensitivity of the sensor and the effectiveness of the IR cut-off filter. Fortunately, with digital imaging, the correct exposure can be gauged by looking at the LCD and the histogram.

Replacing the IR cut-off filter with a clear filter may affect the color rendition in normal use, but will increase the effectiveness of an external IR filter. One interesting application of this conversion is the ability to shoot an image twice (from a tripod), once with the IR filter in place and once without. In Photoshop, you can combine the two images and selectively include color in your IR photograph.

If you replace the IR cut-off filter with an internal IR filter, you can achieve either partial or total IR capture. A less powerful IR filter will allow both visible light and infrared light to pass through. The result is an unusual color rendition. A pure IR filter will allow only IR light to record on the sensor; this option gives the truest black-and-white IR capture possible with current technology.

Two companies I can recommend for IR conversions are Life Pixel (www.LifePixel.com) and MaxMax (www.MaxMax.com). There are other vendors now doing this work; do a search on IR camera conversions.


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