Lighting 102: Distance

Lighting 102: Distance, originally uploaded by timothylarson.
I'm not rushing through these exercises, partly because I've ordered a second light set-up after Sam Parsons, a friend of mine, expressed some interest in going through the Lighting 102 exercises as well. But I had enough free time today, that I figured that I had to do at least the next short section... distance. This was another very basic section that talked about the inverse square law without getting into the math and technical aspects of it... David, from the Strobist blog explains it like this:

"The closer you are to the light source, the more powerful the light. Get real close and it gets really powerful. Get far away, and it gets weaker... The closer you get to the light source, the quicker the lighting values change as you move in. When you get farther away, small differences in distance (from the light) become meaningless."

So, the related exercise was to take three photos of your subject with the subject staying in the same spot, move your flash closer and further away. While keeping the subject relatively well exposed watch to see what happens to the light falling on the background. As you can see in my photos above, the closer I had my light to my subject (Sprinkles) the faster the fall off of light, therefore the darker the background became. Zack Arias puts it this way:

"If you double your distance from flash to subject, you lose 75% of the light.  To me it seems like if you double distance then you lose half of your light but some dudes and some ladies... figured out that is not the case.  You double distance from flash to subject you lose 75% of the light.  Not 50%.

"In Myth Busters type of science that means when you double distance you lose 2 stops of light.  If you double one foot that means you lost two stops of light at the two foot mark.  If you double 20 feet… you lose two stops at the 40 foot mark."

Once you get this in your head, it becomes easier to control the exposure of your subject and background the way you want them to be exposed. I'll leave you with this little Q&A that I found today:

Q. How come old photographs are always black and white? Didn't they have color film back then? A. Sure they did. In fact, those old photographs are in color. It's just that the world was black and white then. The world didn't turn color until sometime in the 1930s, and it was pretty grainy color for a while, too. Q. But then why are old paintings in color?! If the world was black and white, wouldn't artists have painted it that way? A. Not necessarily. A lot of great artists were insane. Q. But... But how could they have painted in color anyway? Wouldn't their paints have been shades of gray back then? A. Of course, but they turned colors like everything else did in the '30s. Q. So why didn't old black and white photos turn color too? A. Because they were color pictures of black and white, remember?

~Bill Watterson - Calvin and Hobbes

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