Once in a Blue Moon – A Trick with Digital White-balance

This week, I got the “once in a blue moon” opportunity to photograph an actual “blue moon”, which we had Thursday and Friday nights.  For the uninitiated, a “blue moon” is the term used to describe the second full moon to occur within a single calendar month.  The term actually has absolutely nothing at all to do with the moon’s coloration whatsoever.  I, on the other hand, finding humor with the term and aware that one was approaching, decided to test a simple theory and waited to try out on an official “blue moon”.  My theory was that I could actually make the moon a nice eerie shade of “blue” with my camera without using any computer software by simply setting the camera’s digital “white balance” parameter to “tungsten light” (the yellow/brownish “white” light produced by normal indoor incandescent light-bulbs).

A typical digital camera will offer several predefined values based on the typical types of light.  For example, my Pentax K-x offers the choices of “daylight” (sunlight), “cloudy”, “shade”, “fluorescent light” (three types), “tungsten light” (incandescent light), “flash” (the camera’s built-in strobe), and “auto” (let the camera decide).  For a normal moon shot, I would select “daylight” since moonlight is simply reflected sunlight.  Taking a picture of a sun/moon-lit scene with the camera set for “tungsten” (2850 kelvin on my camera) yields a very bluish image, hence the “blue moon photo you see here! I was able to do this by manually setting it to this value.  I normally get the best results outdoors using the “daylight” setting and indoors with “tungsten” or one of the fluorescent settings based on the type of light.  “Auto” often seems to work better when there’s a mixture of different types of light with no single one particularly dominant.  With film, none of this is applicable, though actual physical glass filters are sometimes used; but with a digital camera, it is an additional variable that often must be set manually in order for the digital camera sensor to properly interpret the scene’s dominant lighting as to what actually constitutes “white” as it appears to the human eye.  Most digital cameras will attempt to determine this automatically, but sometimes a photographer will need to manually set this parameter to best capture his scene as he intends.

I also had to manually underexpose by about 5 stops in order to get the details of the moon’s surface without flair.  I used my 90mm Tamron macro and did massive cropping, rather than my 55-300m (kit) zoom because my 300m lens simply can not produce images as sharp when zoomed out 200-300m as my much more expensive macro can, even after the additional cropping.  The final photo was taken at 1/640″, f6.3, iso200 (90mm) around midnight (fully clear, dark sky).  I did not use any other filters or editing.

I’ve also found this setting useful for taking yellow sunflowers in the very golden evening sun in order to bring out the yellow color of the flowers against the green leaves (see photo):


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