day 60 - pimpin the inverse sq law

allright. so, the inverse square law states (if i might paraphrase poorly here) that light falls off logarithmically from it's source. you can see this if you look at a light bulb right next to a wall.... it goes from being very bright, to being medium bright very quickly, then slowly rolls down to not very bright over a much longer distance.

observe this graphic, stolen from wikipedia:



explained a lot, didn't it?

so, who cares? how can this be used and abused? usually you're going to use this by positioning people in the "long slow falloff from medium bright to not very bright" zone, because the light there is very even for a very long time. so even if you have ten people, spread out over twenty feet, they'll all get the same (more or less) amount of light, and no one will be way way brighter than anyone else.

but what if you want a subject that is lit brightly, but very little light on the background?

that was my idea. in this picture i wanted to take advantage of the quick falloff that occurs very very close to the lightbulb. in order to do that i had to make that quick falloff reach a little further, since i at least want to be slightly visible in the picture.

so, of course, counter-intuitively: if you want the background wall to be dark, you have to turn up the power of your strobes.

which i did. then i closed the aperture of my camera down to f22, and took some shots. adjusted the subject to light distance a bit (at this level of closeness, it's easy to blow out the subject's highlights..... that exponential curve can do some damage), took some more shots, and finally got this one.

now, there's easier ways to do this. it's really easy to put a "gobo" (a go-between) between your strobe and the background, guaranteeing that less light will hit the background. but i wanted to challenge myself and do this with nothing between the strobes and the background. light still got back there, lots and lots of it, but by the time it got there is was (comparatively) weak. that ten feet separating me from the wall resulted in light hitting it that was way way darker that the amount of light on the subject.

it is kinda cool, using this sort of extreme falloff curve.... the light on the subject has a bit of a different feel to it. it falls off faster, defines the shapes differently..... it almost reminds me of when you put something on top of a photocopier and use that to make a crude image that way. makes me want to shoot something very curvy with this setup. be interesting for a pregnancy shoot.

i pushed up the "fill light" in lightroom for this pensive setup shot: