The Exposure Triangle: Doing the Math to Make a Nice Picture

When I was in college (which feels like so many moons ago!), I took an Intro to Photography class. I took the class because, with the easy availability of digital cameras, I had already started taking a ton of photos but wanted to do it a little better. I didn't know what an SLR was (or what those letters even meant) and had no idea about all the different components you can manipulate to take a picture, all to different effect.

Beautiful Sunday by Jen Gallardo
Beautiful Sunday — one of my favorite photos as it makes a nice desktop background!

I think I ended up getting a film SLR (that's single-lens-reflex, by the way) camera for Christmas and using that for a while throughout the class but the exposure triangle kind of alluded me for a long time. It wasn't until I started using a digital SLR — with the abundant low cost tolerance for trial and error — that it finally clicked.

A lot of people ask me about what kind of camera to buy and use but, for most of those people, I think the question they should be asking is how they can improve the quality of their photos.

That only comes with understanding the exposure triangle. Since most folks I know are using (expensive!) digital cameras, I'll limit the explanation to digital (but the same applies more or less for film).

So, to start, I'll just clarify that photography is really the art of capturing and manipulating light to create an exposure. An exposure, to simplify, is your image. To some degree, you use a camera as a tool to conjure up an image that may or may not represent what you actually see with your eye. It's fun to think about the fact that you are bending light through time to make stuff — almost feels like the future, except when you realize this stuff has been around for hundreds of years.

That said, you need light to make a picture. What you do with the light is where the exposure triangle comes in. And, as you'd expect with a triangle, there are 3 key components: aperture, shutter speed and ISO.

City Lights by Jen Gallardo
City Lights — there's a triangle in here, along with all the lights…

I'll quickly summarize these three as they often seem really complicated but aren't — also, for those of you who don't like math, you can rest assured that it really isn't at all complex.

Aperture controls the funnel of light that pours into your camera. The aperture can be very wide, letting a lot of light in, or very narrow and doing the opposite and letting a sliver of light in. Think of it like a firehose and you can control how much comes through the hose. The smaller the number, the larger the funnel of light. This seems counterintuitive, so think of it as fractional pieces of a pie; 1/16th of a pie is much smaller than 1/8th of a pie which directly translates to f/16 being a smaller funnel of light than f/8 (and so forth).

Next is shutter speed which simply controls how long you let the light into your camera. To continue with the fire hose analogy, you are deciding how long you keep the hose open. For most typical photography needs, this is being measured in fractions of a second. Back to the math again! Essentially, when you see a shutter speed that is 125 this is actually 1/125th of a second. So, in keeping with what we said about aperture that means that a larger number here lets in less light; 1/125th of a second is smaller than 1/100th of a second so a shutter speed of 125 is going to allow less light to come into your camera than a shutter speed of 100.

The last of the three is ISO which represents the sensitivity of your camera's sensor to the light (I'm oversimplifying but that's all you really need to know). To keep with our analogy, think about ISO as the porousness of whatever you are aiming the firehouse at; the higher the ISO, the more light will be absorbed. This means that an ISO of 1600 will absorb way more light than an ISO of 100 (which is usually the standard baseline for most cameras and appropriate for lots of sunny day shooting). No fractions here — bigger always means more light.

Generally, you are shooting for a balance among these three. So, as I sit by the Hudson River on a sunny day, I might make my aperture f/16 and make my shutter speed 125 and leave my ISO at 100. If that's too dark, I need to add more light. I can add more light by either making the aperture wide (smaller number), making the shutter speed slower (smaller number) or making the ISO higher (higher number). This is where the trial and error can come in as you will need to experiment changing one variable at a time until you arrive at the desired result. And, as you continue to experiment, you'll find some conventions that always seem to work. One rule a lot of photographers use is "sunny 16" meaning that, if it's very sunny, start with your aperture at f/16 and adjust the other numbers relative to that.

Sunbathing in Paradise by Jen Gallardo
Sunbathing in Paradise — this is a perfect example of the "Sunny 16" rule in action

And I would be incredibly remiss if I forgot to mention that sometimes changing these variables may result in some side effects that may or may not be what you intended (unless, of course, you've done all the trial and error and start to spot the patterns and adjust your exposures accordingly…).

A few side effects to look out for include:

Ornate Camera by Jen Gallardo
Ornate Camera — I didn't really want to capture the backdrop in the Museum of Ice Cream, just the funky-looking camera

If you make the aperture too wide (smaller number), you might find you have less of the picture in front of you in focus. While the aperture controls the size of the funnel, it also controls the "depth of field" or how much of your picture can remain in focus. More to come on "depth of field" as there are lots of different creative reasons why you might want to play with this. In the above photo, you can see that there's nothing wrong with this — unless I intended to capture more detail in the background.

Car pulling away by Jen Gallardo
Car pulling away — to show that this car is moving away from me, it made sense to do a longer exposure to try best to capture the motion without video

If you make your shutter speed too slow (smaller number), you might find it harder to "freeze" the action in front of you resulting in a lot of "motion blur" if the things in front of your camera happen to be moving. Because the shutter controls for time, moving objects can be a challenge when you have that funnel open for a longer period of time. Again, there are creative reasons why you might want to have the funnel open longer (like astral photography, for example) so that's another topic to be covered another day! As you can see in the above example, I wanted to show that the train car was moving and you get that sense here because of the motion blur present.

Dark Alley by Jen Gallardo
Dark Alley — not really sure where I found this dark alley but I probably will never go back here…

If you make your ISO too high (larger number), you might find the resulting pictures you take don't look super sharp or may even look a bit grainy, especially when you try to enlarge or print. Your digital "film" (if you will) can only tolerate so much light. It's sort of like our skin and the sun. Get a good amount and you can get a nice tan, get too much and you might get burned and it varies per person. The same is kinda true about ISO and I'd recommend limiting your exposure to it, much like the sun! If you are in a crazy dark environment, you'll need to bump up your ISO and how "burned" you get will depend on a lot of factors. That said, depending on your subject matter, sometimes you want the grainy effect of a high ISO (like when you take photos of musicians in a dark bar). If not, you may even need to add light to your scene; this is where external flashes or other lamps would come in which is a yet another topic for another day. In the above photo, my ISO was all the way at 1600 and this photo is pretty grainy if you zoom in, which is acceptable for a dark alley!

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