Photography exposure – Using the water in a bucket theory

Clear your mind and imagine this. It’s a challenge. To start things out, imagine you have a water faucet. There is a hose attached to the faucet. At the other end of the hose, there is a bucket.

When you open the faucet, water flows through the hose and into the bucket.

Once the bucket is filled to the top, you successfully complete the challenge.

You fail if the bucket that overflows or if the bucket isn’t filled up.

Simple. Right? And it definitely would be, but imagine that you had to do this with your eyes closed.

You couldn’t visually see the bucket filling, and instead you had to give instructions to a machine that would do it for you.


Now you may ask yourself:

How long should I keep the faucet open for enough water to flow through and fill up the bucket?

How fast is the water flowing? Water that flows faster is sure to fill the bucket faster.

How big is the hose? A bigger hose would be able to deliver more water.

How big is the bucket? A smaller bucket will be full sooner than a bigger one.

All of these are valid questions, and with a few tries you might actually fill the bucket to the brim!

But believe it or not, this concept of filling a bucket with water is, in one way, how you should think about photography as you balance your shutter speed, aperture, and ISO so that you get a photo is isn’t too dark and isn’t too bright/washed out.

In photography, we don’t deal with streams of water. We deal with rays of light.

This, in photographic terms is called: EXPOSURE.

How will you EXPOSE the film or the sensor in your digital camera to light?

How long? How much? How big is the “bucket” that you need to fill?

In the water/faucet analogy, think of this when you compare to your camera

How long you open the faucet for = Shutter speed

How wide the hose is = Aperture

How big the bucket is = ISO

How strong the water pressure is flowing out of the faucet = The strength of your light source

Sometimes you will have the power to control all of these factors. You will be able to choose whatever shutter speed you want, the aperture, the ISO and your light source.

This is typically a studio situation.

Other times, you will only be able to control a few of these, for example if you are shooting outside. The sun (or stars) will provide light for you, and you have to adjust the other three to compensate so that you “fill the bucket” .

You may keep the shutter open for a split second when the sun is bright, or you may keep it open for a while as the trace amounts of light can trickle into the camera when shooting at night.

An important thing to note is that adjusting your shutter speed, apeture, and ISO has an effect on how the final image looks, and I dive further into it in their own dedicated tutorials.

Just remember, the water in a bucket analogy is just one part of photography, that I feel is something every person learning this craft should know and apply.