There’s a Hole in the Bucket: Photography 101

It has never been easier to get a good-looking photograph from a camera than it is now. As a result more people than ever are enjoying photography. It’s easy to get clear results with no technical knowledge, but it’s now also harder to understand the fundamentals because they are behind electronic controls.

A Foggy Orchard on Old Mission by Thomas Kachadurian

I made this photograph a few days ago with my iPhone. The original image is fairly well detailed. The exposure wasn’t great, but I fixed that in Photoshop.

Critical functions and adjustments are automated and hidden from the user making it difficult to develop an instinctive understanding that was second nature for analog photographers. As a result we have many would-be photographers who have only a vague idea what’s going on in their cameras.

To the casual user who wants photos to share and post on-line it doesn’t matter at all. However basic technical knowledge is the first hurdle to anyone who wants to improve his or her work, dig deeper into photography, or be able to get consistent repeatable results. Technical knowledge is about getting what you intend each time you release the shutter. As good as they are, cameras can still only give good results most of the time, not all the time. Some of the situations where we most want photographs (the high school gym comes to mind) are the most challenging to photographic automation. And even the best camera won’t make a great photograph without a skilled user.

I have been teaching what’s hidden in electronic cameras for more than 15 years, and I consistently see that technical understanding allows my students to increase their enjoyment of photography and make more and better photographs. In the next few months I am going to walk through technical fundamentals. These are things I learned over years as a photographer. I learned these things slowly, in bits and pieces. I am going present them in the same small steps.


The Holy Trinity: Aperture, Shutter Speed and ISO

When I started out it was a challenge to get a properly exposed photograph. My Tower (from Sears) camera had no meter and I used the printed insert in the roll of film to guess at exposure. It’s laughable now, but I learned exactly what those settings were doing.

Bracelet made to look like the Aperture Ring on an old Nikkor lens by Thomas Kachadurian

There was a time when these numbers were on every lens. Now you’re more likely to find them on a wrist band.

Nobody worries about exposure anymore. Cameras will get you close, and when the camera is wrong a file can be improved in Photoshop. At the same time, no photographer will ever progress without understanding the three essential elements of exposure: Aperture, Shutter Speed and ISO. Understanding the elements of exposure is the first step to taking complete control of photography.

My favorite analogy for exposure, the hole in the bucket, is from the photography textbook by Barbara and John Upton I had at Wayne State University in the 1970s. I have explained this so many times, over so many years, that the Uptons should no longer be blamed for how I’ve tortured their simple explanation.

If you think of light as a substance like water it gives it a more quantifiable nature. The correct exposure of a photograph is the skill of getting exactly the right amount of light to the sensor. For the sake of the analogy, think of the sensor as a container of light. Imagine that container as a pint glass. Our goal is to exactly fill this container. If we allow too much light we overflow the container and make a mess. If we under fill the container we don’t have all of the resource that we need and our sensor is starved.

Light is everywhere, so we don’t think of it as something that flows. But just like water light can be measured. Think of the world of light as a bucket of water. To exactly fill our pint glass we make a hole in the bottom of the bucket and put in a spigot to control the flow. If the hole is very small we have to open the faucet for a long time to get our full pint. If the hole is large we need only a few seconds of flow. Either way our container must be exactly filled.


The hole in that bucket is the APERTURE of the lens. The aperture changes the size of the hole to allow more or less light to flow. We use a numbering system to get precise sized hole for the light to flow through. Aperture is often called F-stop. More correctly, the numbers we use to denote aperture increments are F-stops.

F-stops are whole steps as follows:

Aperture illustration copyright 2016 Thomas Kachadurian

Shutter and Aperture dial example by Thomas Kachadurian

The smaller value denotes a larger opening. Each of these whole stops is half the amount of light of the value preceding it or double the light of the value following it. Cameras with electronically notated aperture will show partial values between these whole stops. On your camera you might see f3.6 or f6.7. These are values between the whole steps.

The spigot is our shutter, and we control the time of the flow with a SHUTTER SPEED. Light flows much faster than water so we express the amount of time the faucet is open in fractions of a second. Most shutters have a fastest speed of 1/4000 or 1/8000 of a second. As with aperture, cameras with electronically controlled shutters aperture will show partial values between the whole stops, making the direct relationship between shutter and aperture much harder to see. Most higher end digital cameras will allow you to choose 1/2 or 1/3 stop display increments. I highly recommend choosing the 1/2 stop option. Doing so only effects the readout. In any automatic mode the camera will still be able to set a precise 1/117 of a second, it will just report it to you as 1/125.

The whole steps for the shutter are more mathematically clear as follows:

1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1, 2, 4, 8, 15, 30.

Many electronic camera displays will not show these numbers as fractions, choosing instead to show only the denominator of the fractions and then noting the whole seconds with the letter “s” or even with just a quote mark:

2000, 1000, 500, 250, 125, 60, 30, 15, 8, 4, 2, 1″, 2″, 4″, 8″, 15″, 30″.

If you have a camera that uses this notation be careful. 2 equals 1/2 a second and 2″ equals 2 full seconds.

In all cases, the shorter the interval, the less light that reaches the sensor. Each step allows double the amount of light than the interval before it. The important thing to note is that Aperture and Shutter intervals relate to each other. Each step represents an equivalent change in the amount of light.


The size of the container is expressed in calculated amounts too. We can think of ISO as the size of the container we want to fill. Back in the analog days, you had a roll of film, and it had a fixed ISO. The container was fixed until you changed film. Now, with digital cameras we can dynamically adjust the size of our container from one frame to the next. A large container, low ISO will require more light to fill. A small container, higher ISO, will require less light. The least sensitive ISO we will find on most cameras is 100 or 200, requiring the most light. Each doubling of the ISO values is a whole step requiring half as much light. Each of these whole steps represents the same amount of light in one step of aperture or shutter speed. Electronic notation of ISO will also show values between the whole stops. Most cameras, in their custom menus, will allow you to limit the ISO readout to only full stops. I highly recommend this setting, particularly for beginners. The whole steps are as follows:

More light needed < ISO 100, ISO 200, ISO 400, ISO 800, ISO 1600, ISO 3200 > Less light needed.


Each of these values, particularly Aperture and Shutter Speed, have an effect on the final photograph. They must be balanced within the trinity to get a correct exposure. One step in each of these values represents the same change of light. If you let more light in through a larger hole, you need to reduce the amount of time the light flows. If you have a smaller container, you need a smaller hole and less time. For example the following combinations all yield the same balance of light/sensitivity, and thereby will yield the same exposure level in the image.

ISO400 @ f5.6 @ 1/250 = ISO200 @ f11 @ 1/30 = ISO1600 @ f4 @ 1/2000

The automatic camera will choose only one of the many possible correct exposure combinations. In the example above, it would probably choose the first combination. Which is just fine for getting the right amount of light, but won’t necessarily give you the photograph you want. The second set would be a much better setting for a landscape photograph, and the last combination would be a much better choice to capture your kids running around the backyard.

Aperture tool by Photographer Thomas Kachadurian

So what setting do you use? Ah! For that you’ll need to check back for the next lesson. Until then, Click on the photo above to download the handout and make your own Aperture/Shutter Speed slider to get an idea of how many combinations are possible. Yep, there’s homework. Comments are turned off on my blog, but if you have questions just email.

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