Exposure Explained

I get it. You have a love/hate relationship with your fancy camera. You love the idea of improving your photography skills and taking great shots of your family. That’s why you invested in such a high quality camera, right?

On the other hand, you probably don’t love the fact that it rarely comes out of its bag because, quite frankly, your iPhone takes pretty fantastic photos, is a LOT less bulky and is always at hand.

Or maybe you use it a lot but just aren’t getting the results you know are possible.  You “see” the shot you want but the camera isn’t producing it.  Those dials and buttons can be manipulated to create a beautiful image, but how?

The camera modes can be so overwhelming. A? S? TV? What? Let’s not even think about M!  Understanding what these buttons and dials do and when to use them requires understanding Exposure and what happens every time you click that shutter button.

Let’s get to know these three key factors by diving into The Exposure Triangle.

We’re going to take a look at ISO, Aperture and Shutter Speed and learn how all three work together and affect each other to create a photograph.

It may seem pretty overwhelming and possibly a lot more technical than you expected, but stick with me and it will all come together. And please remember, PRACTICE.   It will become muscle memory, I promise!

I’ll start with an overview of what is actually happening when we take a photo.

When we press the button on our camera, the shutter inside our lens opens and closes. While the shutter is open, light enters the inner chamber of the camera to reach the sensor. The sensor captures the light and turns what you see in your viewfinder (or on the back of your camera if you’re in Live View) into a photograph.

There are two controllable factors here: how wide the shutter opens (Aperture) and how long it stays open (Shutter Speed).

Both of these factors impact how much light is reaching the sensor. 

Let’s talk about Aperture first.


visual explanation of aperture online photography class

The size of the shutter’s opening is called APERTURE. Aperture is measured in f/stops – f/2.8, f/5.6, f/11, etc.

The way it’s measured seems a little counter-intuitive, right? The SMALLER the number (f/1.4 for example), the BIGGER the shutter opening.

Pro Note: Shooting at f/1.8 or f/2.8 is considered shooting “wide open” because the shutter opens all the way.

The wider the shutter opening (so, the smaller the f/stop), the more light can get to the sensor.  Why do you want the ability to shoot as wide as possible?  A couple of reasons:

  1.  A lens that lets us shoot at 1.8 or 2.8 or 3.5 will give us a lot more flexibility in lower light conditions.  No windows? No problem – adjust your f/stop down to 1.8.
  2. Shooting wide open offers BEAUTIFUL bokeh – essentially, the blurry background look that we all know and love.  The smaller that f/number, the blurrier the background will be.  It’s such a great way to create a point of interest in the photo and cause the viewer to be drawn to whatever portion of the image is in focus.

Your lens, not your camera, determines the aperture range, so it varies from lens to lens. Most basic kit lenses (the lens that came with your camera) can only “open up” to f/4.0 or f/5.6, making it pretty hard to take indoor photos without turning on the flash. My favorite starter lens, the 50mm f/1.8, opens to f/1.8 and is only about $100!  Here’s the 50mm for Nikon and here it is for Canon

With all lens purchases, make sure you click on the “Enter your model number to make sure this fits” link to ensure the lens will work with your camera!

I’ve covered the creative side of Aperture in a separate blog post – check it out!

Shutter Speed

How long the shutter stays open is referred to as SHUTTER SPEED. It’s measured in seconds – 1/60, 1/125, 1/200, etc. A shutter speed of 1/60 means that shutter is staying open for 1/60th of a second.

When we set our shutter speed to, say, 1/125th of a second, we’re able to freeze movement and capture a clear depiction of what we are seeing through the viewfinder.  However, if we slow that shutter speed down to 1/15th of a second, it’s open long enough to capture some movement, so the final image will be blurry.

1/60 or 1/125 is typically fast enough to avoid blurry photos of people.  However, if you have a fast moving toddler, 1/200 or 1/250 might be a safer!


ISO is the final point of the Exposure Triangle.  If any of you took a film photography class in high school or college, you’ll remember film speeds – same concept.

ISO is a measure of the sensor’s sensitivity to light.  The higher the number, the more sensitive the sensor is and therefore the less light you need to capture your image.  If you increase your ISO, you can more easily capture an image in a low light situation, however, that comes at a price – the higher the ISO, the more “noise” (visual distortion) you’ll see in your final image.

The lower the number, the less sensitive the sensor is, so you’ll need more light.  The image, however, will be very clear.


A lot of information, right?  Here’s a quick overview:
  • ISO
    • sensor’s sensitivity to light
    • high ISO when you don’t have a lot of light (inside, evening)
    • low ISO when you do have a lot of light (outside, daytime)
    • high ISO = lots of digital noise
    • low ISO = clear, high quality image
  • Aperture
    • how wide the lens opens when you take a photo
    • measured in f/stops
    • low numbered f/stop (1.8, 2.8, etc) = larger opening = more light hitting the sensor = blurry background
    • high numbered f/stop (8.0, 11, etc) = smaller opening = less light hitting the sensor
  • Shutter Speed
    • how long the shutter stays open when you take a photo
    • measured in fractions of a second
    • fast shutter speed freezes movement
    • slow shutter speed captures motion

When you’re shooting in Auto mode, your camera is deciding the ISO, Aperture and Shutter Speed.  It’s going to pick whatever settings are needed to get an accurately exposed image (an image that isn’t too dark or too bright).

The creative modes (P, AV, S [or TV] and M) let you take control of one or more of these settings so you can create photographs that are more, well, creative! 

Lucky for you, I’ve created a 10 page guide that explains the creative modes in an easy to understand and actionable way. Download it today!

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