Thank you all for the kind and encouraging words on my previous posts from my Southwest trip – I really appreciate it. Here is one more from the sandstone paradise. In my past couple of posts I’ve shown you some wonderfully colorful images from sandstone slot canyons. The truth, however, is that even the most colorful canyons are still just a dull red color, except when the sandstone catches the light just right.

In the middle of a sunny day there are essentially two sources of natural light: the sun (directed broad spectrum light), and the blue sky (diffuse omnidirectional blue light). Of course, ultimately the source of the light coming from the blue sky is also the sun, but let’s consider it a separate source for now. As an aside, the blue color is due to Rayleigh scattering – the preferential scattering of short wavelengths of light off of small particles in the air. Since blue is the shortest wavelength of visible light, it is the predominant color that is scattered.

In direct sunlight (broad spectrum) colors appear as they “should” – objects absorb certain wavelengths of light, and reflect the rest (which is what we see). Under narrow spectrum illumination, such as blue light, only blue light can be reflected. As a result, everything will appear a little blue, even objects that aren’t normally dominated by “blue”. Think for example of shadows in the snow, which are caused by objects or people blocking sunlight. These shadows are not totally black because scattered light from other directions, usually primarily light from the blue sky, also illuminates the shadowed areas.

In a slot canyon the direct sunlight undergoes multiple reflections. In the first reflection only red light is reflected since the surface is red. The reflected light is scattered in all directions, so only a small fraction of it bounces deeper into the canyon. In each subsequent bounce the intensity is reduced even further. At some depth there is so little light left from the reflections that the diffuse light from the blue sky is more intense than the reflected light. The result is a mixing of the warm tones of reflected sunlight and the cool tones of the light from the blue sky, resulting in a rainbow of earthy colors, which I call the Navajo Rainbow.

Click image for larger view!

Reflected Light in a Slot Canyon, Arizona, Southwest

Navajo Rainbow : Prints Available
Reflected light in a sandstone slot canyon.

Exposure: iso 100, f/16, 4 sec
The Tech: Canon 5D2, 70-200mm, tripod
Notes: 4 exposures at different focus settings hand blended for depth of field.

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4 Comments to “The Navajo Rainbow – Sandstone Slot Canyons”

  1. Matt Curtis says:

    I’ve been following your site for a year or more now, and I think this is my favorite photo. You’ve got some mad skills!

  2. I have to agree with Matt. This is absolutely stunning and definitely one of your best!

  3. A really exquisite picture Floris – and the maximum depth of field is adds a great visual ‘pull’.

  4. Thanks folks, I appreciate the kind words! This was one of my favorites from the trip too.