Monday, July 30, 2012

The Light Pile/Bucket Theory

To support my assertion that the technical stuff is trivial, I introduce the light pile theory.

A picture is made up, more or less, of little dots. On every dot, there is a little pile of light. The bigger the pile, the brighter the dot. Itty-bitty-tiny pile, the dot is pretty much black. Big tall pile, white. If the light piled up is mostly green, green dot.

Exposing a photograph just means letting light in to pile up for a while. Make the hole light passes through bigger, more light piles up on each dot -- this is the aperture. The word aperture even means hole. Let the light pass through for a longer period of time, you get bigger piles again. This is shutter speed.

It's just like filling a bucket. If you use a bigger hose, you fill for less time. If you fill for less time, you need a bigger hose. If you want to stand around filling for a long time, use a smaller hose.

That's all there is to exposure.

If one pile of light is twice as big as another, we say the first one is "one stop" brighter. If you leave the shutter open twice as long, twice as much light piles up. That's one stop. Or, if you leave the shutter alone, but make the hole twice as big (1.4x as wide -- that's geometry), twice as much light piles up. That's one stop as well.

Ok, there's one more thing about exposure: ISO, which is just how big of a pile makes "white". The higher the ISO, the smaller the pile you need to make "white". Make the ISO twice as big, you only need a pile half as big to make white. You can also think of it has how big your bucket is.

So you wanna fill a bucket up. You can use a big fat hose for a really short period of time, or you can use a medium hose for a medium amount of time, or a really skinny hose for a long time. (wide open aperture, fast shutter speed; medium aperture and shutter speed; closed down aperture, slow shutter speed). Or you can use a bigger or smaller bucket (ISO).

Your camera probably tries to get all the buckets, on average, filled up halfway. That way some buckets are full, some are empty, and most of them are in the middle. So your picture has some black parts, some white parts, but mostly it has parts that are between the two. If it's nighttime, the camera doesn't know that, but you probably want you picture to look dark, like nighttime. That means your light piles all need to be smaller, you want to fill the buckets up less. How do you fill the buckets up less? Smaller hose (aperture), or fill for less time (faster shutter speed), or use bigger buckets (lower ISO). Similarly if your scene is supposed to be bright and light (maybe you're photographing a bride's dress, here in the USA where they are white): Bigger hose, slower shutter speed, smaller buckets.

There's a few subtle details here and there but you really don't need to know one single damn thing more about the technical nonsense of photography, even if you're going for a pretty fine level of control. You probably don't need to know this much. Most of the people going on about technology and urging you you to learn about this and that probably don't know as much as this.

It's just making little piles of light, or filling little buckets with light. It works the same as water, except the names are all different.

P.S. Wider apertures (bigger holes, bigger hoses) use smaller numbers. 2.8 is bigger than 4.0 is bigger than 11. Go figure.

No comments:

Post a Comment