Saturday, June 1, 2013

A Lunchtime IR Ramble...

A couple years back I got a used camera off of EBay with the intent to convert it for infra-red photography
(IR). Back when I was a pup back in my high school and college days, I'd often shoot the occasional roll of IR film.  In those days Kodak made 3 versions of the film, an IR sensitive, a high--speed version and a color version as well.  Of course, these days film is pretty much dead, though I believe there is a European IR film still being made.

The digital sensors in cameras are also sensitive to IR light, but because our eyes are not sensitive to it and it can play havoc with imaging and color balance, it is normally filtered out with a pre-sensor filter.  I arranged for the 20D camera to have the IR-blocking filter with an IR-pass and viola - a dedicated IR camera.  I've done a few posts before and it is fun to observe normal-looking scenes in literally "a new light"!  The "Wood's Effect", discovered by an early pioneer, makes healthy plants look brilliant white and the clear blue sky very dark, which are the main attributes to IR imaging...  A friend of mine expressed interest, and I offered to loan it to him for a while, so the other day took it to work to remind myself how it all works!

The image at left shows a comparison with a visible light image taken with my normal camera at the same time of a pot on our stoop.  You can see that the vegetation appears white, but the glazes on the talavera pot have quite different IR reflectivities than their visible equivalents.  The darkest shades are from the lightest blue color...

Another shot before I even left the yard presented itself with the last quarter Moon next to my neighbor's palm tree.  While the moon appears the same in visible and IR, it is the reflectance difference between vegetation and sky shown here that makes up the Wood's effect.  With the ready appearance of the moon in the bright day lit sky, I'm thinking that with the darker sky one could try to image stars in the daytime, though I've not yet tried it!

At lunchtime I ambled over to the Student Union for lunch and at the library, a similar ultimate IR image presented itself.  The tall palms against dark sky make for quite a dramatic image.  And just past the entrance, one of my favorite sculptures "Girl with Doves" by David Wynne makes a nice 3D image, particularly with the vegetation and sky and library as background.  This is my normal crosseyed-view 3D view - cross your eyes slightly to examine the left image with right eye and vice-versa.  The center image will reveal depth of the 3D image...

The well-manicured grounds of the campus make a multitude of shots available, and now that school is out until summer school starts, most of the University is vacant.  At left is the south side of the Student Union. At right is the administration building.

Upon my return to work, I ran into one of our students, Morgan, who offered to serve as model to illustrate the effects of IR for portraits.  Obviously it isn't a very flattering version - her pretty auburn hair is mostly neutral or blue-tinted, eyes are pretty dark except for the whites, and skin is transformed to a uniform ghostly white...  Interestingly, there are slight color tints in the above images from slight differences in the red/green/blue filters that are still just beneath the IR transmitting filter in the sensor.  I've imaged a spectrum with this camera and it reveals the furthest IR part of the spectrum as bluish, so the blue filter may have a leak allowing some tints.  With Morgan's "blue" hair tint, we can amp up the saturation and use the hue controls in Photoshop to transform her to a redhead as shown at right.  We also get the sky back as blue in this version, but other than this image, all the IR images shown above are straight out of the camera, save for some contrast adjustment...  Fun stuff indeed!

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