Exposure in 7 Shots

Got 2 minutes?  ...like literally, 120 seconds?  Sweet.  Grab your camera, we're going to take 7 quick shots and demystify this exposure setting stuff once and for all.

Shot #1:

Pick up your camera and walk outside onto your front steps, breezeway, or whatever.  Just get outside.  Set your camera's Exposure Mode to Aperture Priority (for most cameras, this means turning the dial on top to "A").  Now, set your aperture to f/5.6.  Find something nearby to focus on, about 3 or 4 feet away.  I used the broken flag bracket on my front porch.  Make sure that whatever's in the background is decently far away, like your neighbors house or a tree across the street.

Next, look at your shutter speed.  To avoid screwing with more settings later, we want it to be about 125 right now.  If its lower than that, gradually increase the ISO setting on your camera until you end up somewhere between 100 - 160 on shutter speed.  If your shutter speed is higher than that, gradually step down your ISO until you get in that range.  Just to get you in the ballpark, if its bright and sunny outside your ISO will probably be 100 or 200.  If its cloudy or moving on towards dusk, it might be 400, 800 or maybe even 1600.

Reframe your shot, focus on the nearby object you chose, and pull the trigger.

Shot #2:

Change your aperture to f/16.  Reframe, focus on the same nearby object, shoot again.  That's it!

Now compare Shot #1 vs. Shot #2.  Notice that the nearby object (my flag bracket) is equally in focus in both images.  But look at the difference for the far away objects in the background.  They are blurry in the first shot, taken at f/5.6 (shallow depth-of-field).  They are much sharper in the second shot, taken at f/16 (deep depth-of-field).  Congrats, you now understand aperture's effect on depth of field!

Shot #3:

Turn around, open your door, and take a shot into your house.  Its much darker inside, so you should hear your shutter take its sweet time opening and closing.  Look at the picture and zoom in.  See how blurry everything is?  This is because you are hand-holding the camera at a very slow shutter speed.  What you're seeing is the dreaded "camera shake"!

Shot #4:

Walk back outside.  Set your camera's Exposure Mode to Shutter Priority ("S").  Set your shutter speed to 500 (1/500th of a second).  Hold out your free hand and focus on it.  Now pull your hand back, and swing it slowly through the frame.  Shoot when you see your hand in the middle of the viewfinder.  Check your shot.  See how your hand is frozen in place?  (If it's not, you were pretending to pitch a fastball, so slow down and try again.)

Shot #5

Set your shutter speed to 125 (1/125th of a second) and do that thing with your arm again.  Swing it the same speed, shoot when it hits the middle.  See how your hand is all blurry?  Now you understand how shutter speed effects moving objects.  Fast shutter speed = frozen in place.  Slow shutter speed = movement looks blurry.  Two more to go!

Shot #6

Set your camera's exposure mode to Program Mode ("P").  Change your ISO to 1600.  Shoot something, subject isn't as important this time.

Shot #7

Dial your ISO down to 100.  Reshoot the exact same shot.

Compare shots #6 and #7.  Zoom in allll the way on the same area in both shots.  See the grainy speckles in shot #6 (ISO 1600)?  That's noise.  See how much smoother everything is in shot #7 (ISO 100)?  Now you understand the affect of ISO on image quality!

DONE!

Shutter Speed & Motion Blur

Shutter speed plays a huge role in how motion is portrayed in a photograph.

If the shutter speed is high enough, moving objects will appear to be frozen. This is the case in the image below. The shutter speed was approximately 1/320th of a second, almost fast enough to make the water droplet appear totally frozen. As it is, the water drop appears mostly frozen with just a little blur around the edges. Not a perfect example, but you get the idea.

In the next image, I've slowed the shutter down to one full second. The water drops have now blurred together, looking like a trail of dust or a strand of spider web. Had I turned the water up a little higher, it would be more visible, but I want to compare oranges-to-oranges here and only change the shutter speed. The thing to remember here is that a slow shutter speed blurs moving objects.

Like I said above, a slow shutter speed causes moving objects to look blurry. However, this rule applies to anything that moves, including the camera itself! If the camera moves when you're using a slow shutter speed, everything in the image becomes blurred. This is called "camera shake".

In the top image, the fast shutter speed is "freezing" all motion, whether we're talking about the falling water droplet or my unsteady hands. In the image directly above, a tripod is holding the camera still, so the slow shutter speed isn't causing any camera shake. Only the water is moving, therefore that is the only part that appears blurred. In the bottom image, I am hand holding the camera while using a one second long exposure. Blur city. You can see why camera shake is considered a bad thing...

So how fast does your shutter speed need to be to prevent camera shake? The answer is about 1 to 1.5 times your focal length. We'll cover focal length later, but just file that away in the back of your mind for now.

Ok, so what did we learn? Use a fast shutter speed to freeze action and keep your images free of the dreaded camera shake. Use a slow shutter speed (and a tripod) to convey motion, whether you are shooting traffic or waterfalls. Handhold at a low shutter speed if you are forced to in dark conditions, but be sure to hold it steady as a rock if you don't want a unrecognizable blur instead of a photo.

Up next... ISO.

Exposure Part 2 - Shutter Speed

Let's move on to our next exposure setting: shutter speed.

Your brain can have a break on this one, because shutter speed is much simpler to understand than aperture. A shutter is just a light-proof curtain that covers and uncovers the film or digital sensor inside your camera for a specific period of time. Normally, the shutter curtain is closed, protecting the image sensor from light until you are ready to take a picture. When you press the shutter button, the shutter uncovers the sensor for a certain amount of time and then immediately recovers it. The amount of time that the sensor is uncovered and exposed to light is called the "shutter speed".

Fortunately, shutter speed uses normal, familiar units: the second. Shutter speeds are generally given in fractions of a second rather than decimals (i.e. "1/8", not ".125"). This doesn't mean all shutter speeds are less than a second long, in fact some exposures can take several minutes or even multiple hours in special situations, but most of the time you will be dealing with fractions of a second.

Like aperture, the difference between shutter speed settings is talked about using "stops". A difference of one full "stop" (whether we are talking about aperture or shutter speed) is either double, or half, the amount of light. With shutter speeds, this corresponds directly to either doubling the shutter speed or halving it.

For example, here's a progression of shutter speeds, all one stop apart:

1/15, 1/30, 1/60, 1/125, 1/250, 1/500

The longer the shutter is open, the more light makes it into the camera. The shorter the shutter speed, the less light admitted.

Let's revisit the garden hose analogy. If I turn on the hose for 15 minutes, I'm going to get a certain amount of water. If I leave it on for twice as long, 30 minutes, I'm going to get twice as much water. This may be too much water, it may be too little, but the point is I can control how much water I get by changing how long I leave the hose turned on. The goal is to get the correct amount of water for the container I'm trying to fill, whether that's an Olympic swimming pool or a Dixie cup.

The same is true for photography. You want to get the "right" amount of light to create a correct exposure. Next we'll talk about the final piece of the puzzle, sensitivity (or ISO, or film speed).

PS - shutter speed, like aperture, affects other things besides exposure, such as sharpness and whether moving objects appeared blurred or frozen. We'll get to that later on when we discuss how to use shutter speed creatively.