What is Exposure? An Adventure in Aperture, Shutter Speed, and ISO

Exposure is a pretty crucial element of your photography, but learning how exposure works can be a little tricky. So, for all of you awesome photography novices out there, here's a post that will help you understand how your aperture, shutter speed, and ISO all work together in creating a perfectly exposed photo.

Down below you'll see the exposure triangle, which is your key to understanding exposure. Don't be afraid. We'll walk you through it. It's your new best friend.

Each side of the exposure triangle above represents one component of the exposure system. Each component affects how light enters your camera and how much is let in. The combination of all three components working together determines your exposure.

Now here's the important part: one component cannot be adjusted without affecting the others. Valuing one component over the others means sacrificing potential benefits from the rest to preserve the valued one. That's not necessarily a bad thing, but it means you have to choose your priorities. Do you want a fast shutter speed so you can capture action? Do you want more or less depth of field? Once you understand this triangle, you'll be able to prioritize for what you want and adjust each of the three components accordingly.

Let's break each of the three exposure components down:

Aperture is like the human eye, which dilates to allow more or less light to pass through the lens. Lower aperture values mean more light is passing through the lens while higher aperture values mean less light is coming in.

Your aperture also determines your depth of field, which is the distance between the nearest and farthest objects in your photo that appear sharp. Think of it this way—you're taking pictures in a forest filled with trees. A low aperture value means fewer trees are in focus in your shot. A high aperture value means more trees are in focus. So, at f/2, you'll only have a couple of trees in focus whereas at f/11, you'll have more trees in focus.

Shutter Speed
Your shutter speed acts as a 'gate' of sorts. You already determined how MUCH light to allow through, and now you choose the shutter speed to determine how LONG to let that light pass through to your sensor.

Faster shutter speeds mean less light passes through. It also means you'll capture movement more quickly. Slower shutter speeds mean more light passes through. It also means you'll capture movement more slowly, possibly resulting in blurry photos.

ISO is a measurement of how sensitive the camera's sensor or film is to the light coming through your lens. As you increase your ISO, your sensor is increasingly sensitive to light. So, in low-light settings, you might up your ISO a bit to get more out of the little light that's available.

Sometimes you'll need to favor one component of your triangle and adjust the other two accordingly. Say you're taking a photo and you only want your subject in focus. You're at f/2, and you really love it there, but the photo is too dark and you need more light. What do you do?

You can either decrease your shutter speed to let the light hit the sensor for a longer amount of time OR you can up your ISO so your sensor is more sensitive to light. Either of these options has pros and cons—slower shutter speeds up your chance for blurry photos, and higher ISOs may add grain to your shots. You just have to play around with your settings until you get it just how you like it.

There's the basics of the triangle. If you'd like to get a little more nitty gritty, read on!

Exposure, Stops, and Dynamic Range
You've probably heard the word stop thrown around a lot in photography speak. Often you'll need to go up or down a stop to adjust your exposure to be just how you want it.

So what exactly is a stop? A photographic 'stop' is a relative change in the brightness of light determined by doubling or halving the amount of light captured.

Let's say we are in a room with a single lightbulb, and this is our normal exposure.

  • If I add one more lightbulb, I have two lightbulbs, and the exposure is now +1 stop.
  • To go up another stop (to +2 stops) I have to double our current lighting of two bulbs by putting four lightbulbs in the room.
  • Going down a stop requires halving the amount of light, so to get back to our 'normal' exposure of one bulb we have to half the light twice. 4 -> 2 -> 1.

Adjusting any one of the three sides of the exposure triangle alters the exposure of your photo by adding or subtracting light, so over or underexposing by a stop requires doubling or halving one of your component's values. Each component also has intermediate values that create 1/2 and 1/3 stops. This allows you to gain a full stop by increasing two of the components by 1/2 stop.

Below are the standard scales for each exposure triangle component with full stop intervals:

1.0 / 1.4 / 2 / 2.8 / 4 / 5.6 / 8 / 11 / 16 / 22 / 32
(Because aperture values are calculated by measurement of dilation, the numbers don't double like the other two components of the exposure triangle.)

Shutter Speed
2" / 1" / 1/2" / 1/4" / 1/8" / 1/15" / 1/30" / 1/60" / 125" / 1/250" / 1/500" / 1/1000" / 1/2000"

100 / 200 / 400 / 800 / 1600 / 3200 / 6400 / 12800 / 25600

Whew! Thanks for sticking with us through all of that. We hope that all makes sense and you are feeling a little more comfortable with aperture. Feel free to leave any questions below in the comments! And if you'd like to see another photography concept explained, leave a request below as well. Happy shooting!

(PS...if you want to understand exposure more, we highly HIGHLY recommend Understanding Exposure by Bryan Peterson. One of our favorite books out there.)

ApertureDynamic rangeExposureExposure triangleF stopIsoMarch 2013Shutter speed