Crash Course-Exposure

This is a crash course in the Big Three of photo exposure.  I’ll run through a quick discussion of aperture (f stop), shutter speed, and ISO, and follow up with how you control them on a Canon DSLR interface.

So, the Big Three:

  • Aperture (f stop): The size of the hole in the back of the lens. (typical values: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22…)
  • Shutter speed: How long the ‘window’ in the camera is open. (typical values: 1, ½, ¼, 1/15, 1/30, 1/60, 1/125, 1/250…)
  • ISO: The sensitivity of the sensors.  This used to be the film speed. (typical values: 100, 200, 400, 800, 1600…)

These three things together determine how much light is captured by a single photo. Too much light, and everything is washed out. Too little light, and everything is super dark.

Small mistakes or variations can be perfected in software, especially if you shoot in RAW instead of JPG. For years, that was my standard workflow. On the other hand, if you get the exposure right in the camera, you’ll save yourself a lot of work on the back end, when you’re done and all excited to share your photos.

All three constraints work together: change one, and you’ll need to change at least one of the others.

  • One f-stop LOWER DOUBLES the amount of light coming through the lens.
  • One f-stop HIGHER cuts the light in HALF
  • LONGER shutter speeds let in MORE light
  • SHORTER shutter speeds let in LESS light.
  • When ISO DOUBLES, light sensitivity DOUBLES
  • When ISO HALVES, light sensitivity HALVES


Okay, let’s walk through some examples. Starting with:

ISO 400, Shutter Speed 1/60 sec, and f/4

Now, let’s adjust the camera for different situations while keeping the same exposure:

Ex. 1: Longer exposure

Let’s say you’re shooting a waterfall and you want a little bit of blur where the water moves. You decide to double the exposure time. (A 1-stop change.) To have the same exposure, our settings would be:

  • ISO 200, Shutter speed 1/30, and f-stop 4 (f/4), or
  • ISO 400, Shutter speed 1/30, and f/5.6

Ex. 2: Bright ambient light

You’re outside in the daytime and you want to have a super-low-noise shot.  You choose ISO 100. (A 2-stop change)

  • ISO 100, Shutter Speed 1/15, and f/4, or
  • ISO 100, Shutter speed 1/60, and f/8, or
  • ISO 100, Shutter speed 1/30, and f/5.6

Ex. 3: Portrait with great bokeh

You’re taking a picture of a friend, and you want only them to be in focus, while everything behind them is fuzzy. You decide to open all the way up to f/1.4, which gives a really shallow depth of field. (A 3-stop change.)

  • ISO 400, Speed 1/500, f/1.4, or
  • ISO 200, Speed 1/250, f/1.4, or
  • ISO 100, Speed 1/30, f/1.4

Ex. 4: Meh, Whatever

You’re still learning/being artistic/DON’T TELL ME WHAT TO DO!

Really, the best way to learn is to adjust things, play with the settings, make bad decisions, and take oodles of photos.  Then, take notice of the settings you really liked.

How To:

First, PUT YOUR CAMERA IN MANUAL. At least for now. I think most DSLRs include the semi-manual aperture priority and shutter priority modes, but the easiest way to see all of the options available is in full manual mode.

On the Rebel series:

To change the settings:

ISO: Press The ‘UP’ arrow, then select the ISO you want.

  • Shutter speed: rotate the selector wheel near the shutter button
  • F-stop: press and hold the “Av” button, then rotate the selector wheel

For the 6D M2

So the New Hotness has the ability to adjust these settings on the touch screen or with wheels and buttons.  Pretty swank.

Press the Q button to start the touch screen-palooza.

  • Tap twice on the setting you’d like to change, then chose the new value. OR:
  • Tap once, then use the selector button near the shutter button to adjust the value.


  • ISO: Press the ISO button and then use either wheel to select the value
  • Shutter speed: Rotate the selector wheel on top of the camera.
  • Aperture: Rotate the wheel on the rear of the camera

Exposure meter:

The exposure meter is a quick, handy way to see if your exposure is ‘correct.’  You can find it on the rear screen or in the viewfinder.

The meter updates each time you half-press the shutter button.  If the indicator’s on the left, the exposure is dark (underexposed).  If it’s on the right, the exposure is bright (overexposed).  Each ‘notch’ away from center is one ‘stop’ – so exchange one of the Big Three by that number of stops to bring your shot back to ‘correct.’