occasionally technical tuesday: apertures and shutter speeds and iso (oh my!)

(A note: this post is the longest and most technical we will ever get on Occasionally Technical Tuesday.  Seriously, it's a beast, but it's a good one -- this will tell you exactly how you can take full control of your camera.  I promise, if you hang in there with me, whole new photographic worlds will be opened to you.  You can do this.  I know you can.)


Okay, folks, so far we've talked about how to buy an SLR camera and how to choose your lens; this week, we're going to go seriously technical -- I'm going to teach you how your camera works. 

I know this sounds intimidating.  And trust me, I also know you can just pick up your camera, set it on fully automatic, and go.  And that's totally fine, really it is.  But honestly?  If you really want to get good shots out of that expensive camera of yours, understanding ISOs and apertures and shutter speeds can give you a lot of power over your resulting shots.  So I promise:  if you stick with me in this post, I'll break it down as simply as possible, and trust me, it'll be worth it (even though the sketches that follow are a travesty to art).  If you're just starting out, do not read past the string of asterisks near the bottom of this post.  It will confuse you.  Just stop at the asterisks.  Understand everything above the asterisks first, play with your camera to make sure you do, and only then can you go forward.  You've been warned.

(Another note:  if you're not ready to learn all of this, and are very happy with shooting fully automatically thankyouverymuch, then at the very least, do yourself a favour and read the ISO portion of this post.  Even if you're shooting fully automatically, ISO is, by far, the easiest to understand, and will likely help improve your photographs noticeably.)

You ready?  Strap in.  I promise, I'll be very gentle.

So basically, your camera, regardless of brand, whether it's a point-and-shoot or SLR, or how simple or complicated it is, works like this:

1.  light enters your lens;

2.  the light passes through an aperture in your lens;

3.  then it goes through the shutter in the camera body;

4.  before it finally hits the film (or sensor/storage media, if you have a digital camera); and then

5.  it magically turns into a photograph.

Obviously, there's a lot more physics to it than that, but dude, I'm not a physics major, and believing that it's "magic" is a lot more interesting, so go with me on this.

Graphically-speaking, and viewing your camera from the side, it looks somewhat like this:

Now:  I could try to draw exactly what each of these items actually looks like, but clearly, sketching isn't my strong suit. Nonetheless, it turns out that you really don't need to know what they look like, but it's sort of important to understand what they do.  And to help illustrate this, take a look at this image:

I know this looks kind of crazy, but stay with me:

Your aperture acts sort of like a curtain:  it decides how much light in total you want going into your camera.

Your shutter acts like a door that quickly opens and shuts, limiting the amount of actual light that gets to the film/digital sensor, regardless of the total amount the aperture actually let into the camera in the first place.  Think of it this way:  remember, back in the day when your dad had a film camera, and the biggest catastrophe that could occur on vacation was that the back of his camera would open up, and all that light would get in and ruin the film, rending those shots of your mom dancing around with a sombrero on her head in Guadalajara completely useless?  That's because too much light overexposes the image.  The shutter opens and shuts really quickly, so that only the right amount of light gets in, and the image is correctly exposed.

And finally, the film (sensor/memory card) acts like a basket, capturing the remaining light and using magic to turn it into a photograph.

With me so far?

Now, the very cool thing about your camera (and what you may not have realized if you've been shooting with everything in automatic mode this entire time) is that in many cases, your camera allows you to control each of the aperture, shutter speed and film/digital sensor capacity.  It's almost like there are tiny little people living in your camera, just waiting for your command:

At the risk of your suspecting that I've completely lost the plot, I'll press on.



As I mentioned above, the aperture helps control how much total light goes into the camera.  Now, if you've ever heard the term "f-stop" or seen weird numbers like "f/1.4" or "f/13" on your camera lens or next to an image online, those terms are referring to how open or closed the aperture (or in our case, the "curtain") is, and therefore how much light is going into the camera.  There are, of course, mathematical reasons for the number designations, but really, knowing that isn't necessary.  Here's the main thing you need to remember:

If the aperture number (f-stop number) is large, then when you take a picture, you'll have more detail in the background of your image (i.e., a "large depth of field.")

If the aperture number (f-stop number) is small, then when you take a picture, you'll have less detail in the background of your image (i.e., a "small depth of field.")

I know. This is confusing.  Some practical examples should help.

Say you're taking a vacation in the American heartland, for the express purpose of capturing an image of those "amber waves of grain."  Or, instead perhaps, you're in Houston, in my overgrown front garden.  Here are a couple of images you might get, when playing with the aperture of your camera:

I shot the image above at f/13 -- "13" is a pretty large aperture number.  Notice how you can see the slats of the black shutters on the house, and you can see the branches and leaves behind the main branch that I was focusing on in the foreground.  The details are pretty easy to make out no matter where you look in this shot, so you would say this image has a "large depth of field."

Now, contrast the above with the following image:

Same branch in the foreground, but this time, I shot it at f/1.4, which is, in comparison to the above, a small aperture number (1.4 being far less than 13).  And yet, the lens is the same, I'm standing in the same spot, and I took the image at the same time of day.  However, in this image, you can't make out any details other than the branch in the foreground -- everything else is out of focus, and therefore this image has a "small depth of field."

Does this make sense?

Therefore and ergo, going back to your vacation in the American heartland: instead of the camera doing everything for you, you can move the camera off of fully-automatic, and change the setting to "A." You are now in Aperture-Priority Mode, allowing you to control the aperture, or the "Curtain-Opening Guy," in the graphic above.  Look at you go!  The camera will worry about the rest of the settings (except for ISO, below), never you fear.

Now, before you take the photograph, you think to yourself:

"Self, do I want to show how vast the amount of grain is in this field, so that all of the grain is in focus? If so, then I'll tell the Curtain-Opening Guy to set the camera to a large aperture number." 

and then you move the setting to a large number.  Or, alternatively,

"Self, would I rather focus on this one golden reed of grain, and blur all the rest around it?  If so, then I'll tell the Curtain-Opening Guy to set the camera to a small aperture number."

and then you move the setting to a small number.  Then you'll aim, and you'll shoot.  Bam.  Beautiful shot, no Photoshop required.



So, as you'll remember from above, this is the part of the camera that acts like a door, opening and closing quickly, to moderate the amount of light that actually gets to the film/digital sensor at the back of the camera, and thus creating the best exposure.  And there's one application where you might want to really play with your shutter speed setting, and that's to control movement.

Here's what I mean:  you'll find shutter controls described in seconds, or fractions of a second, otherwise known as "exposure time."   

With a long exposure time, the shutter will be open longer, and movement will look blurry.

With a shorter exposure time, the shutter will be open for a shorter time, and movement will look frozen in time.

Here's an example:

In this photograph that I took several years ago ...

... I shot it at a shutter speed of 1/160th of a second.  Notice how the water looks like it's rushing over the rocks.  There's movement and blurriness, and it conveys what it sounded like on that beach in Cozumel, Mexico.

However, in this picture ...

... I shot this at 1/250th of a second, which is much faster than 1/160th.  Because it was faster, it made the water coming out of my backyard hose look almost frozen in time.  It makes it look extra refreshing, doesn't it?

So, again, back to you: say you want to take photographs of your daughter's track meet.  In this case, what you might consider doing is moving the camera to the "S" setting (the "Shutter Priority" mode), allowing you to take control of the shutter speed, or in our example, the Door-Opening Guy.  G'head.  Give it a try.

Dude, can you feel the power? 

And again, the camera will take care of any other settings for you (except for ISO, below).  So, before the starter gun goes off, you'll think to yourself:

"Self, I want to my daughter to look like the fastest freakin' blur possible as she races past me.  So I'm going to tell the Door-Opening Guy to set the camera to a low speed number, so that the door closes slowly, and I capture her movement."  And then, you do so.


"Self, I want to capture an image of my daughter so that it looks like she's frozen while leaping over that hurdle.  So I'm going to tell the Door-Opening Guy to move quickly, to catch the shot -- and so he's got to have a high-speed door slam happening up in there."  And so, you set the camera to a high speed number, and you're good to go.



Okay, folks, we're almost there:  the last thing we're going to talk about is ISO.  In my opinion, this is the most important thing a beginning photographer needs to know about, even if you're shooting with your camera fully automatic.  So:

Remember back in the day when you were buying film, the box of film would have numbers on it like "100" or "400" or "1000"?  That was the film's ISO number.  ISO stands for "International Organization for Standardization" (I know that mixes up the initials, but I didn't come up with the acronym, so don't blame me), and basically the ISO number has to do with the sensitivity of film to light.  Nowadays, with digital cameras, there are still ISO settings, and understanding how they work can help you vastily improve your images.  To help me remember what those numbers mean, as shown below, I like to think of the ISO number as "the number of light catchers" the camera needs to use:

In other words, remember this:

The lower the ISO number, the fewer light catchers you'll be using to catch the light and put it in the magical basket.  Low ISOs work best in bright sunlight -- no flash necessary.

The higher the ISO number, the more light catchers youll be using to catch as much light in the camera as possible to put in the magical basket.  High ISOs work in overcast or low light -- and again, no flash will be necessary.

For example -- see that photograph of my garden hose, above?  That was taken at an ISO setting of 200, because it was taken in the middle of a hot summer day, and there was tons of available light.  So I knew that I only needed 200 light catchers to catch the light when the shutter ("door") was open to let the light into the camera.  Contrast this with the following shot I took of Marcus this weekend:

This was taken at sunset in our very dark living room, just as the sun was dipping behind the houses and trees in our neighbourhood.  The light was low, so I knew that I needed to use as many light catchers as I could to grab any and all available light:  this was shot at an ISO setting of 3200.

And finally, compare the shot above to this one:

This shot was taken at the same time, but this time the setting was at ISO 200.  See how completely blurry and out of focus Marcus is?  That's because the Door-Opening Guy (shutter control) went, "SERIOUSLY?  TWO HUNDRED?  In this nonexistent light?  That's SO not enough Light Catchers.  I'm going to have to keep the door open longer to let more light in, and expose the photograph properly."  So he did -- the shutter was open for a half a second (as opposed to hundredths-of-a-second, like the garden hose, above).  The problem is that when the shutter is open for that long, the slightest movement -- my hand holding the camera dipping ever so slightly -- causes blur in the resulting image.

Given all of this, it sounds like you'd never need a flash again, right?  Just crank up that ISO setting, and bam! No flash needed!  Well, not quite:  the problem with using high ISOs is that while you might get the image in the brightness you want, the image tends to be grainier or "noisier" than at low ISO settings.  So if you're looking for a nice sharp image in low light, you might want to either (a) use a flash (which, of course, will distort the light and not capture the ambiance that you're actually seeing) or (b) use a tripod with a low ISO setting -- that way the camera ("Door-Opening Guy") can keep the shutter open as long as necessary, without worrying about camera shake.

As I mentioned above:  ISO is the most basic setting your camera has that you can adjust, and it can make a world of difference if you just have the setting right (and you'll find you'll use your flash far less, even on a point-and-shoot camera).  So at the very least, play with the ISO.  Just remember the light catchers, and you'll be golden.

So that's it -- you're now an expert (sort of) on apertures, shutters and ISOs!*  Better still, that's pretty much as technical as we're going to get here on Occasionally Technical Tuesday.  Just print this out (or bookmark this post), grab your camera, and start experimenting with the settings, have this post within arm's reach to refer to.  After a few times, you'll start to get it, I promise.

And with that, happy clicking, friends.

* * * * * * *

*  A NOTE ON SHOOTING MANUALLY (DO NOT read this until you've really mastered the concepts above; otherwise, this will confuse EVERYTHING):

Once you've mastered shooting in aperture-priority mode or shutter-priority mode, try shooting you camera fully manually.  Here's the only additional thing you'll need to remember:

When the aperture number is large, it means the aperture (or "curtains") is fully closed.

When the aperture number is small, it means the aperture is barely closed, i.e., wide open.

Repeat that to yourself a couple of times -- because it's sort of tricky. 

One more time.

Got it?

Okay.  Now, knowing this, you can start thinking about how each of the ISO, shutter speed and aperture relate to each other.  So, for example, if you're shooting on a bright sunny day, you'll think things like: "Huh.  Lots of light here, so I just need a few light catchers -- I'll set my ISO to 200, which is a low number of light catchers.  Next, I want a pretty small depth of field, so I'll also set my aperture to a low number (because I only want a little bit of the entire picture in focus) .... but by setting it to a low number, I know that it's barely closed (i.e., wide open), so that means a LOT of light is getting into the camera.  So I'd better have a quick shutter speed (make the Door-Opening Guy open and shut the door quickly) so that the photograph isn't overexposed."

See?  I told you this is confusing, and if you've read this part when you weren't ready, dude, I warned you.  (But honestly, don't beat yourself up about it:  it took me years -- years! -- before I felt like I was ready to shoot manually).  Just forget what you read here, go back to the sections above the asterisks, and keep practicing.  However; if you've mastered the concepts at the main portion of this post, that previous example will actually start to make sense.  And if you start to practice with your camera on manual, you're going to discover you can make it do things that it never did before, because it turns out that cameras aren't nearly as smart or creative when they think as you are. 

And you are.


Occasionally Technical Tuesday is a new feature here on Chookooloonks, where we'll tackle topics like choosing a camera, how a camera works, how I choose lenses, how I use Photoshop, how I pack for a photo trip, that sort of thing.  You can see an entire index of subjects we've addressed here.  I'm no expert, but I'll share what I know, occasionally.


SongKodachrome by Paul Simon

Karen Walrond48 Comments