Through the Gadling Lens: apertures and shutters and ISOs, oh my!

So, so far, we’ve discussed two things: how to pick a camera and what kind of lenses you might want to take with you on your trip. Today, I thought we’d talk about the exciting world of apertures, and shutter speeds and ISO.

Wait, where are you going?

Okay, I know that for a majority of you, you couldn’t care less about these sorts of things — you’d rather just pick up your camera, set it on automatic, and go. And I promise, going forward, we’re going to talk about less dry subjects, like shooting techniques and using Photoshop and the like. But the truth is, understanding ISOs and apertures and shutter speeds can help give you a lot of power over your resulting shots. So trust me on this: it’ll be worth it, even though the sketches that follow are a travesty to art.
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: light comes into your lens, and passes through an aperture, then through a shutter before it finally hits the film (or digital sensor and storage media), and then 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 those items actually looks like, but as you’ve probably guessed by now, 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 what they do, 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 you had a film camera, the biggest catastrophe that could occur on your vacation was that the back of your camera would open up, and all that light would get in and ruin the film, rendering all those great images of you doing tequila shots in Tijuana 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 (or digital sensor/memory card) captures the remaining light and uses magic to turn it into a photograph.

Now, the very cool thing about your camera (and what you may not have realized if you’ve just been shooting on automatic this entire time) is that in many cases, it 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 believing that I’ve finally lost it, 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/16” on your camera 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 only 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., your background will be more detailed, 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 depth of your image (i.e., your background will be less detailed, a “small depth of field“).

Some practical examples might 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, perhaps instead, you’re in Houston, in my overgrown front garden. Here are a couple of images that you might get, when playing with the aperture on your camera:

I shot the image above at f/16, which is sort of a large aperture number. Notice how you can make out the detail of each of the little slats in the black shutters in the background, and the foliage in front is just a jumble of branches. Everything, pretty much, is in focus, or you would say that this image has a “large depth of field.”

Now contrast the above with the following image:

This image was shot at f/4.2, which is, in comparison to the above, a small aperture number — the lens is the same, I’m standing in the same spot, and I took the image at the same time of day. In this image, you can no longer really make out the detail of the black shutters, and in fact, the only thing in focus is the branch at the very front. Everything else is out of focus, and therefore this image has a “small depth of field.”

Does this sort of make sense? Therefore and ergo, going back to your vacation in the American heartland, back to those amber fields of grain, before you take the photograph, you can think to yourself, “Self, do I want to show how vast the amount of grain is in this field, and therefore use a high aperture setting, so that all of the grain is in focus? Or, Self, would I rather just focus on this one golden reed of grain, and blur all the others in the background, so I should use a small aperture setting?” Then you’d set your aperture, you’d aim, and you’d shoot. No Photoshop required.


Remember, 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/digi
tal sensor at the back of the camera
, and thus creating the best exposure. I will be honest with you — I rarely, if ever, try to control the shutter speed of my camera. I’m far more likely to mess with my aperture settings (the “curtain guy”) to control my depth of field (how blurry I want my background to be, described above), or my ISO setting (the “light catchers,” which will be discussed below), and let the camera figure out which shutter speed would be most appropriate. That said, there’s one application where you might want to 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 more blurry. With a shorter exposure time, the shutter will be open for a shorter time, and movement will look frozen in time.

For example, this shot …

… was taken 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, it conveys what it felt and sounded like to be there on that beach in Cozumel, Mexico.

But in this picture …

… the shutter speed was at 1/250th of a second — much faster, making the water coming out of my backyard hose look frozen, and therefore more refreshing on a hot summer day.


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 acronym, so don’t blame me), and basically the ISO number has to do with the sensitivity of the film to light. Nowadays, with digital cameras, there are still ISO settings, and understanding how they work can help improve your images. To help me remember what the numbers mean, I like to think as 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. Low ISOs work better in bright sunlight — no flash necessary.

The higher the ISO number, the more light catchers you’ll be using the catch the light. 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 taking at an ISO setting of 200 — because it was taken in the middle of a hot summer day, there was TONS of available light. So I knew I only needed 200 light catchers to catch the light when the shutter (“door”) was open to let the light in. Contrast this with the following shot I took of my husband this past weekend:

This was taken just as the sun was dipping below the horizon. The light was low, so I knew I needed to employ 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 above shot with this one:

This shot was taking at the same time, but this time the setting was at ISO 500. See how completely blurry and out of focus Marcus is? That’s because when I decided to shoot at 500, the Door-Opening Guy (the automatic shutter control) went, “SERIOUSLY? FIVE 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 2.5 seconds. The problem is that when the shutter is open for that long, the slightest movement — my hand holding the camera dipping ever slow 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 you want, the image tends to be grainier then at low ISO settings (contrast the quality of the first image of Marcus with the image of the hose, above). So if you’re looking for a nice sharp image in low light, you might want to either (a) use a flash 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.

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 about the workings of your camera here at Through the Gadling Lens, so never fear. As it happens, I’m leaving at the end of this week for a two-week holiday to England, so for upcoming posts I’ll talk about planning for a trip, and executing photo shoot days. In the meantime, keep clicking those cameras!

Karen is a writer and photographer in Houston, Texas. You can see more of her work at her site, Chookooloonks.
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