Category Archives: Aperture

September 24, 2007 · 10:04 pm

Aperture: Why You Care

flower f/22At this point, we know that aperture is how big the opening in the lens is when you take a picture. We know that big numbers mean a small opening (and therefore less light getting in), and small numbers mean a large opening and more light. f/4 is a large aperture, which means lots of light. f/16 is a small one, and only a little bit of light.

Aperture does way more than control how much light gets into the camera. Those “f-stop things” are one of the most useful tools in photography. Let’s look at why.

I stopped at a park on the way to work this morning so that I could take pictures of flowers to use as examples in this lesson. The flowers weren’t particularly remarkable, but they were useful patient subjects. Here’s one example. You’ll probably look at it and think, “Yeah, a yellow flower”, and see it as fairly messy and uninteresting. That’s because it is messy and uninteresting and an entirely unremarkable picture. Its purpose in life is to serve as a bad example, and it does a rather fine job of it.

Here’s the exact same flower from the exact same angle, but it’s a much more compelling photo. When you look at it, your eye is drawn to the flower, and it isn’t distracted by all the stems and leaves and junk and crap and ick in the background. The only difference between the two images is that in the first one the background is in focus, and in the second it’s soft and blurred.flower f/4

“Hey, that’s cool! How can I do that?”

It’s easy! All you have to do is pay a little bit of attention to what’s going on, and change your aperture to get the effect you want.

“Huh?”

It’s time for me to demystify another technical term– this time, it’s “depth of field”. Depth of field is really just how much of your image is in focus. There’s a lot of complicated stuff underlying it, but the basic premise is really simple.

When you take a picture, it’s almost always true that some things in the image will be close to the lens, and others will be farther away. The way depth of field works is very simple– if your lens is very wide open (i.e. small f-stop numbers) only a narrow range of distances will be in focus. If your lens has a very small aperture (a big f-stop number), then a very large range of distances will be in focus.

Confused? I don’t blame you. Let’s have our six-year-old draw us another picture. Imagine that you’re walking through a meadow. In front of you is a yellow flower. A little bit farther back from the flower is the goofiest-looking tree you ever did see, and in the distance is a snow-capped mountain range.

While walking through a meadow, you come upon this scene

Clearly, the flower is very close to your lens, the mountains are far away, and the tree is somewhere in the middle. Let’s pretend that you’re going to take a picture of this idyllic scene, and you decide to focus on the tree.

If you keep your lens wide open, the tree will be in focus but the flower and the mountains will be blurry. If you use an aperture that’s in the middle of the range then you can get the tree and the mountains in focus, and if you use a very small aperture then you can get everything in focus. The former might be useful if you wanted to focus on one thing (say a person standing in front of the tree) and the latter is great for landscape photography.

Think of your depth of field as a stripe that is centered at whatever you focused on. Whatever is inside the stripe will be in focus. If your lens is wide open, then the stripe will be very narrow. If it has a very small aperture, then the stripe is very wide.

I’ll close today with two excellent illustrations from the nature photography of Joe Decker. One shows the power of a shallow depth of field, and the other illustrates what a wide depth of field can do. I highly recommend clicking through to see larger images, since the thumbnails don’t do them justice. Oh, and Joe’s flowers are much better looking than mine.

You’re probably still confused by this, and I don’t blame you. In the next lesson, I’ll leave the fluffy flowery examples behind and show you depth of field in a completely different way. If you don’t want to wait, stick your camera in aperture priority mode and take a bunch of pictures at different f-stops. The wonderful thing about digital photography is that you can play around a lot. The feedback is cheap and very fast.

Next lesson: Quick Exercise: Focusing

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September 14, 2007 · 10:38 pm

What does f/8 really look like?

Yesterday I talked about apertures (a.k.a. f-stops) and how they work. As the old saying goes, a picture paints a thousand words, and this is after all a photography blog. Without further ado, I present f/8:

f8

Pretty cool, huh? That’s what it would look like if you could look inside your lens while you were taking a picture. As you can see, the blades of the diaphram (that’s the thing in the lens that opens and closes to change the aperture) have closed down to make an opening that’s much smaller than the full opening of the lens. What this means is that a lot less light will get into the camera than if the lens was wide open.For reference, here’s what the lens looks like wide open:

f1_8

Notice that you don’t see the blades of the diaphram at all. If you were to look into your camera’s lens right now, you’d see something just like this because the diaphram only closes while you’re actually taking a picture.

The lens in the picture is a Canon 50mm f/1.8 lens. (Aside: if you have a Canon dSLR, I highly recommend buying this lens. At a retail price of less than $80, it’s a screaming deal.) Since it’s an f/1.8 lens, it has a maximum aperture of… that’s right, f/1.8. The minimum aperture is f/22, which is pretty typical for non-specialized lenses.

Here’s what the full range of the lens looks like. I didn’t take a picture of every possible setting, but you can probably figure out for yourself what the ones in-between look like:

f1_8 f2 f3_2
f/1.8 f/2 f/3.2
f4 f5_6 f8
f/4 f/5.6 f/8
f11 f16 f22
f/11 f/16 f/22

A lot of what I’ve been saying about aperture probably makes more sense to you now that you’ve seen those pictures. All other things being equal, a photo taken at f/2 is going to be about a bezillion times brighter than one taken at f/22. That’s because the amount light that comes in through a great big window is way higher than the amount that comes in through a pinhole.

By the way, I apologize for the reflections on the lens. Taking pictures of glass is notoriously difficult, and I was feeling a little bit too lazy to set up enough of a lighting rig to do a better job. Mea maxima culpa. (If you want to learn sophisticated lighting techniques, I recommend the excellent Strobist blog. Stick around here for a bit and master the basics first, though.)

Now you’ve seen my f-stops. Want to see your own? Here’s a little mini-exercise to do just that.

Most modern cameras have a button called depth-of-field preview. On my Canons, it’s if you’re looking at the camera from the front, the DOF preview button will be next to the lens, on the right side, toward the bottom of the camera. It’s just below the button that you use to take the lens off. If you can’t find yours, check your camera’s manual.

Now, set your camera for manual mode, and an aperture of f/8. We don’t care about any other settings right now, because we’re not going to take a picture. Look into your lens, and press the depth-of-field preview button. Did the diaphragm close? If so, you now know what f/8 looks like on the lens you’re using. Try different apertures to see how it changes.

If your camera doesn’t have a DOF preview button, there’s another trick you can use. Set the camera for manual mode, f/8, and about a 20-second exposure. Press the shutter button (yes, take a picture) and look into the lens. You’ll have 20 seconds to look into the lens and see the diaphragm. Like before, you can try out different apertures and see what they look like.

When you started reading this blog, you probably kept your camera in automatic mode all the time. And now, a short time later, you actually know your f-stop from a hole in the ground. If I’ve done a good job, your brain isn’t even bleeding out your ears.

As it turns out, aperture is one of the most powerful tools in photography. In the next couple of lessons I’ll show you why.

Next lesson:  Aperture: Why You Care

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September 14, 2007 · 4:20 pm

What’s that f-stop stuff anyway?

Newcomers to photography are often intimidated by technical jargon. Walk into a room full of photographers, or read camera reviews, and you’ll quickly be overwhelmed by seeming-gibberish about megapixels, spot metering, chroma noise, low-pass filters, A/D converters, sync speeds, and a myriad of other not-quite-English terms. If only you hadn’t cut Swahili class in high school, maybe it would make more sense to you and your head wouldn’t be swimming.

Of all the technical terms, nothing is scarier for the beginner than f-stops. I’ll do my best to demystify them for you.

First off, a simple English lesson. You’ve almost certainly heard the word aperture before… if you’ve been reading this blog, you’ve eve heard me use it. What exactly is it? An aperture is an opening, and specifically an opening that lets light in. In photographic terms, the aperture is the hole in your lens that lets light into the camera.

That wasn’t so scary, was it? No? Good. let’s keep going.

So what’s an f-stop? In a nutshell, it’s how big that opening in the lens is. That’s it. Really. It’s not some magical, mystical thing that’s going to bite you if you get it wrong. F-stops don’t hurt. They’re not contagious. They won’t kick your dog, drink your beer, or max out your credit cards. OK, they might max out your credit cards someday, but only if you start chasing really big ones.

How do the numbers work? Basically, a small number means that the lens has a very wide opening, and big numbers mean that the lens has a small near-pinhole opening. Of course, we remember that big openings let lots of light in, and small ones only let a little bit of light in. The most common f-stops you will encounter will be in the range of about f/2 to f/22. f/2 is a low number, so it’s a really wide opening. f/22 is tiny. Sometimes you’ll see numbers as low as f/1.4 (and if you have deep pockets, f/1.2), or as high as f/32 or occasionally f/45.

Something important to know is that when you aren’t actually taking a picture, your lens is always open to its widest possible opening even if you have the camera set to use a much smaller f-stop. This lets you get as much light as possible for focusing and composing the image. When you press the shutter button to take a picture, one of the things that happens is that little metal blades in the lens come out to make the opening smaller while the shutter is open. This happens automatically, and you don’t need to think about much about the details.

By the way, photographers tend to use the terms aperture and f-stop interchangeably. That’s OK.

Every lens has a minimum and maximum aperture, but they’re usually only rated in terms of the maximum– that is, the widest opening. For example, Canon sells two 50mm lenses. One is the 50mm f/1.8, and the other is the 50mm f/1.4. The first one can open as wide as f/1.8, which is really rather wide. The other goes as wide as f/1.4, which is even wider. (But you knew that!) Other than the maximum aperture, what’s the difference between the lenses? The f/1.8 lens is about $80, while the f/1.4 is about four times that price. Lenses with with very large maximum apertures are called fast lenses; I think it’s because of how quickly they drain your wallet.

Did that all make sense? Was it not too scary?

Tomorrow I’ll show you some pictures of what it looks like inside a lens, and show you a neat trick for checking it out yourself.

Oh, yeah. If you’re confused, feel free to ask questions in the comments. I’ll do my best to answer them.

Next lesson:  What does f/8 look like?

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September 10, 2007 · 4:54 pm

Exercise: exposure modes

Are you ready for the first exercise? Great, let’s go. If you haven’t ready the last lesson on how exposure modes work, you’ll want to do that first. In this exercise, we’ll try out the various exposure modes in order to learn how the controls work.

OK, grab your camera. It doesn’t matter what lens you use, but try to find a place with a lot of light and something at least marginally interesting to point the camera at.

The first thing we’re going to do is put the camera in aperture priority mode. If this is the first time you’ve taken your camera out of its everything-automatic rut, this may be scary for you. Don’t worry, I’ll be right here to hold your hand. Now, take a deep breath and turn the dial to Av, A, or whatever your camera calls it.

See? That wasn’t so bad.

Now, pick out something nearby that you can focus on. Maybe it’s a picture or a piece of furniture or a tree, but pick something that isn’t going to move around a lot. Now, look through the viewfinder of your camera and focus on the thing that you picked out. Press the shutter button halfway, and you should see a display in your viewfinder that will tell you what the aperture and shutter speed are set to.

Turn whatever dial it takes on your camera to open the aperture as wide as it will go– remember, that’s the lowest number. It may be as low as 1.4 or 1.8, but more likely your lowest setting will be somewhere between 2.8 and 5.6. It doesn’t matter for now. Keep pointing the camera at whatever object you picked out.

If you did that quickly enough, which you probably didn’t, you’ll still have a display in your viewfinder. If not, push the shutter button down halfway to get it back. Make a mental note of what shutter speed the camera has picked out. Now, turn the aperture dial a few clicks. Do you see the shutter speed change? (If the display goes away, just keep pressing the shutter button halfway.) Keep doing this until the aperture is as small as it will go– most likely, that will be around 22, but your lens may be different.

Did you notice how the shutter speed changed automatically every time you changed the aperture? That was your camera’s meter picking out the right shutter speed to go with the aperture you chose. It’s possible that your camera had trouble with the highest and lowest settings, and couldn’t find a shutter speed fast enough or slow enough to work. If so, it probably kept the needle all the way on the left or right of the meter display, and maybe flashed it or beeped or complained in some other way. If so, remember that for the future. It’s your camera’s way of saying that something’s not right.

Now, let’s do the same thing but in shutter priority mode. Set your camera to Tv or S or whatever. Look through the viewfinder, and press the shutter button halfway. Turn the magic dial to change the shutter speed, and watch the selected aperture change. If you pick a really fast shutter speed like 1/1000, there’s a good chance you’ll get to see how your camera complains about bad exposures.

OK, there’s one more step, but before we take it you probably need a quick break from all this scariness. Get up, walk around the room, do a jumping jack, grab a beer, or do whatever it takes to get past all the scariness I’ve thrown at you.

Are you back? Excellent. Now, we’re going to do one more scary thing. Set the camera to manual mode. Ready? Deep breath. OK, go.

Still with me? Great! Now, set your aperture to f/8, using whatever control your camera uses to change the aperture in manual mode. Now look through the viewfinder and press the shutter halfway. See the indicator on the meter? It’s probably way off to one side. Keep looking through the viewfinder while you turn whatever dial changes the shutter speed. Keep doing this until the indicator is right smack dab in the center of the scale. When you get it there, take the picture.

Guess what? You just took a photo in manual mode. If you view it on the camera’s LCD, you’ll probably see that it looks pretty good. Pretty cool, huh?

If your room isn’t very bright, there’s a chance that you couldn’t make that work. If so, set the aperture as wide as it will go and try again, or go somewhere with more light.

Next lesson: Shutter speed exercise

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