On most cameras, you’ve got a handful of automatic of semi-automatic modes. One of those is usually Shutter Priority Mode. It’s usually identified with the Tv label on the settings dial. It might also be labeled simply with a “T” or an “S”.

In shutter priority mode, you select a shutter speed. The camera then automatically chooses an aperture value that gives you the proper exposure. This might be a good option if you want to control the amount of motion blur in the picture – choose a slow shutter (i.e. 1/30th of a second) and you can force the camera to capture a little blur. Choose a quick shutter (i.e. 1/250th of a second), and you’ll eliminate most of that blur. Keep reading…

When you look at the dial on top of your camera, there’s probably an option labeled ‘A’ or ‘Av.’ This is “aperture priority mode.”

So what is aperture priority mode?

It’s a semi-automatic mode for your camera. You pick one setting (the aperture), and the camera automatically adjusts the other settings to get the exposure right. This gives you a certain amount of control without forcing you to constantly adjust the settings to maintain exposure (as you would in manual). The camera will automatically choose an appropriate shutter speed (and an ISO level if you leave that on auto).

So When Should I Use It?

Well, that depends. Some people use it almost exclusively, while some people prefer the control of manual. Here are some reasons you might want to consider aperture priority mode…

The Light Keeps Changing. If the lighting level around you is constantly changing, the proper exposure for the camera is changing too. If you’re in manual mode, you’ll need to constantly change the settings yourself to stay within a decent exposure range. If the light changes often, this can be a real pain… and it can also be disastrous if you don’t have the time to make those adjustments.

For example, I was recently at my sister in laws wedding. I was sitting in the crowd, snapping a few pictures of the ceremony. It was outside, and it was mostly sunny – but a little cloudy. When the ceremony started, there was a cloud blocking the sun, which limited the amount of light in the scene. Just as she started to walk down the aisle, the sun came out… increasing the amount of light. With the camera in aperture priority mode, it automatically adjusted the shutter speed. If I had it in manual (which I often do), I would have either a) shot the picture and overexposed it or b) taken the time to adjust the settings and missed the moment. Hmm… neither of those outcomes is very good.

Control the Depth of Field. The aperture controls the depth of field in a picture. There are other semi-automatic modes on your camera (Programmable Auto and Shutter Priority Mode), but Aperture Priority is the proper choice if you want to maintain a certain depth of field. If you want a shallow depth of field, open up the aperture and let the camera pick a shutter speed. If you want a big depth of field, do the opposite. This gives you some creative control without taxing your brain thinking about all the camera settings at once.

Previously, we talked about how shutter speed and aperture affect an image. The third main setting you have to worry about is ISO sensitivity.

Your digital camera creates an image by processing the light that comes into contact with its internal sensor. The ISO sensitivity is a measurement of how sensitive the sensor is to that light. Jack it up, and it will magnify the intensity of the light. Turn it down, and it will minimize it.

What Happens When You Turn Up the ISO Sensitivity?

By turning up the ISO sensitivity, you artificially increase the amount of light captured by your camera’s sensor. This effectively makes the image brighter. For example, changing the ISO from 400 to 800 will effectively double the amount of light captured by your camera.

There is, however, a trade-off. The increased sensitivity to light also means an increased level of noise – little speckled dots that make your picture look… not so good.

The image to the left was shot at 3200 ISO, which is pretty high. The image also came out under-exposed, so I had to brighten it in Lightroom (which also magnifies the noise).

So Why Use a High ISO Rating?

There are three basic things that affect an image’s exposure – shutter speed, aperture, and ISO. Let’s say you’re shooting a sporting event, like the track meet where the picture above came from.

You need a relatively high shutter speed. In this case, I picked 1/160, which isn’t ideal but it’s fast enough.

This also means you’ll need to open up the aperture and let in a lot of light. The maximum width of the aperture depends on your lens, though. At this time, I still had a basic zoom lens that had a wide open aperture of f/5.6.

With those settings and an average ISO of 400, the picture was really under-exposed. I couldn’t lower the shutter speed (for fear of more motion blur), nor could I open up the aperture (because I hit the physical constraints of my lens). My only option was to increase the ISO until the picture was relatively well exposed. I didn’t want the noise, but it was a necessary evil to get the image to come out at all.

So What Are Average ISO Ratings/Uses?

Low ISO. For most cameras, this is 100 to 400. This is great for shooting outside where there’s a lot of light, or when you’re using lights to artificially light your subject. Either way, you don’t need to worry about light, so there’s no need to artificially increase it.

High ISO. This can range from 800 up to crazy levels like 12,800 (not recommended). You’ll often need this for indoor or night sporting events where there is limited light and you still want to maintain a quick shutter. If you’re shooting sports outdoors on a cloudy day, you might also need a medium to high ISO (400 to 800).

As a general rule of thumb, you want to pick your shutter speed, pick your aperture, and then adjust the ISO accordingly.  You want to use the lowest ISO possible, to avoid noise, but if you can’t bring in more light with the other two settings its a necessary evil.

Changing the aperture setting on your camera has a direct effect on the exposure on your image. But it also effects your image in another way. The aperture setting creates what’s called depth of field.

When you take a picture, you focus on a specific point. This would typically be your subject; let’s say a person. As you move away from the focal point – either closer to the camera or further from the camera – the picture moves out of focus. The depth of field describes how big of a range is in focus, and how quickly the picture moves out of focus.

Large Aperture, Small Depth of Field

As the aperture gets bigger, your depth of field decreases. The picture to the left was taken with a relatively large aperture, f/2.8.

The focal point here is somewhere between the two girls faces. Ideally, it would have been focused on one or the other, but the student who took this picture missed the focus a bit. Doh.

Nonetheless, the two faces are relatively in focus, although the girl in the back is beginning to get a little blurry. Beyond her, though, is hopelessly out of focus. The wall is one giant blur. Notice, too, that the foreground of the picture (the gray hood) is also blurred and out of focus. There’s a very small range – about 2 ft here – that’s in focus, and the rest of the picture becomes increasingly blurry.

Small Aperture, Large Depth of Field

This picture was taken on a relatively bright day. Since there was plenty of light around, it was possible to use a smaller aperture (the previous photo was taken indoors, where the amount of light was severely limited). The picture was shot at f/10.

In this case, there is a much larger depth of field. The focal point of the original picture (this was cropped) is somewhere around #53 in the back. However, notice that the running back in the foreground and the linebacker to the left are both in relatively good focus. They’re slightly out of focus, but the depth of field is large enough that they are fairly crisp.

The larger problem with this image is that there’s a little bit of motion blur/camera shake. It was shot at 1/125th of a second, which isn’t quite fast enough to freeze the action at a football game.

So Do You Want a Large or Small Depth of Field?

Well that depends on the type of image you’re trying to create. There are times when each is an appropriate choice.

A common use for a small depth of field is portraiture. By using a small depth of field, the subject (the person in the portrait) is held in tight focus, while the background becomes extremely blurry. This directs the viewers attention to the subject. Similarly, sports photographers often use a relatively small depth of field. This way your subject is in focus but the opposing team’s bench is not.

A common use for a large depth of field is group portraiture. If you’re shooting a large group and you use a small depth of field, only one or two people will be in crisp focus. The rest of the group will fall out. The larger the group, the larger depth of field you’ll want. Landscape photographers also often utilize a large depth of field, since the scenes they capture are so large.

Your digital camera’s aperture setting is one of the three main settings that determines whether your image is well-exposed or not.

Inside your camera is a digital sensor that captures light. The sensor is covered by a pair of doors (the shutter, read more about shutter speed here), which open and shut to allow light in.

However, there’s also a circular door of sorts (called a diaphragm) that covers the sensor. This circular opening (the aperture) expands and contracts to effect how much light comes in and contacts the sensor (see the image to the left, courtesy of Wikipedia). In the top picture, the diaphragm is wide open, creating a large aperture and letting in a lot of light. Conversely, in the second picture the diaphragm is almost closed, creating a tiny opening and letting in a small amount of light.

How Does This Convert to Camera Settings?

The aperture setting on your camera is the one labeled with an ‘f’ – i.e. f/1.8, f/4.0, f/22. This number is a measurement of how big the aperture is.

It is also a bit non-intuitive. The larger the number, the smaller the aperture. So, for example, f/22 is an extremely small aperture which lets in a tiny amount of light. f/1.8, on the other hand, is a very large aperture and lets in a whole lot of light.

So, in terms of exposure, you want to open the aperture (turn the number down) to brighten your picture and close the aperture (turn the number up) to darken the picture.

As usual, though, there’s a trade-off. Read the next post to see how else the aperture effects your image.

Previously, we talked about how the shutter speed effects an image’s exposureand how the shutter speed can lead to motion blur. But is motion blur always a bad thing?

Not necessarily. There are certain artistic reasons that you might want to intentionally blur your photo. Here are some examples.

Panning an Image

Panning is a technique used to emphasize the fact that your subject is moving. The idea is to make the subject come out clear while blurring the background behind the subject.

This is, of course, easier said than done.

In this image, there is a very slight panning effect taking place. The two players are fairly crisp in the foreground, although there is a little motion blur. In the background, though, there is a slight but clear amount of motion blur.

This was accomplished by moving the camera to the left, following the quarterback, while capturing the image. The shutter speed was 1/200th of a second, which is quick enough to eliminate most motion blur but not all of it.

A more effective way of achieving this effect is to use a flash in combination with a slow shutter speed. The flash helps freeze the subject in place (a topic for another day), while the background will come out much blurrier. Of course, that assumes you can hit your subject with a flash, which you wouldn’t do on the sideline of a football game.

Highlighting Fluid Motion

A second reason you might want to use a slow shutter speed and include some motion blur is to emphasize the fluid way that certain things move.  Example? Fire.

Fire is a weird thing. It’s constantly and fluidly moving. If you sit and watch a fire burn, it’s hard to pinpoint exactly where the flame is.

To capture that fluid essence of fire, you want to use a slow shutter speed. This allows the flames to whip around a bit while the shutter is opening, slightly blurring the image and conveying that sense of motion.

Of course, you need to find a happy medium. If your shutter speed is too slow, you’ll end up with an orange mess. The “right” level of blur is a matter of artistic taste, and you’ll need to decide what you think looks right.

Shutter Speed Recap

To recap, there are three things to know about shutter speed.

It affects how much light comes into the camera. A quicker shutter speed means a brighter image, while a slower shutter speed means a darker image.

It can either freeze the action or lead to blurry images. Use quick shutter speeds to freeze moving subjects (i.e. sports), and avoid blurry images caused by motion blur and camera shake.

Sometimes motion blur is a good thing! This is a matter of taste, but sometimes motion blur is a good thing. It’s a tool that you should keep in mind when thinking of how to compose and capture certain images.

One way that the shutter speed impacts an image is by determining how bright or dark the image is.  Read the previous post for more details.

But, as with the other camera settings, there is a trade-off involved. There are certain situations where you will always want a quick shutter speed, and there are other situations where you will want to use a slow shutter speed.

Freezing Action vs. Motion Blur

The problem with leaving the shutter open is that if your subject moves, your image is going to end up blurry. If you’re taking a picture of a moving subject, you need to have a quick shutter speed to freeze the action and prevent motion blur.

In this image, for example, a relatively quick shutter speed helped freeze the runners in place. Yes, they are moving pretty fast, and with a slow shutter speed he would have come out quite blurry. This is the final leg of a 4 x 100m relay. While these high school athletes are no Usain Bolt’s, they’re running as hard as they can.

But the quick shutter speed, 1/1000th of a second, freezes them in place. The shutter isn’t open long enough to register the subjects’ motion, so they appear to be standing still in the picture.

Compare that to this picture, where there is very clearly a motion blur problem.

In this case, my student photographer accidentally used a slow shutter speed (1/30th of a second). Since the football players are moving pretty quickly, they move in the space of time that the shutter is open. This blurs the players across the frame, leading to a lackluster, blurry image.

So What’s a Good Shutter Speed?

Well, that’s a good question. And the answer will vary.

Another thing to look out for is “camera shake.” Instead of the subject moving, the camera itself moves… causing a slightly blurry image. The problem is magnified by longer focal lengths (i.e. zoom lenses). So, as a rule of thumb, you should try to use a shutter speed that’s equal to the focal length you’re shooting at.

If you’re using a 50mm lens, shoot at 1/50th of a second or quicker. If you’re using a 400mm lens, shoot at 1/400th of a second or quicker. A steady hand, a mono-pod, or an image stabilization system can reduce this problem… but the idea is to use a quicker shutter speed with a longer focal length.

Other than that, it’s all relative. If you’re shooting a quickly moving subject (i.e. sports), you’ll want a minimum of 1/125th of a second. Depending on how quickly and in what way the subject is moving… this might be ok. But, you’ll probably get better results if you can get up to 1/250th of a second or faster.

The problem? You still need to let in enough light for the image to come out. If you’re shooting sports outdoors, this usually isn’t a problem. But, if you’re shooting sports indoors, you might have to compromise and settle for a little motion blur in exchange for bringing in enough light.

Is Blur Always a Bad Thing?

Not necessarily. There are certain artistic reasons for including motion blur into a picture. Read the next post on when motion blur isn’t a bad thing to see a couple examples.

One of the three main settings you can adjust on your digital camera is the shutter speed.  Altering this setting will have a direct effect on an image’s exposure – how bright or dark the color is.

So how does the shutter speed effect an image’s exposure?

Letting Light In Over Time

Your digital camera takes a picture by exposing its internal sensor to light. The light comes into the camera, contacts the sensor, and is converted into an image with (hopefully) vibrant colors and crisp details.

This sensor is normally shielded by a pair of doors – the shutter – which keep the light out. When you press the button to take a picture, the shutter opens up, allows a little bit of light in, and then quickly shuts itself.

The shutter speed setting on your camera is a measurement of how long the shutter stays open. Typically, this isn’t very long.  A quick shutter speed (like you would use for sports) would be something like 1/500th of a second – a tiny fraction of a second.  A slower shutter speed (like you might use indoors with a flash) would be something like 1/30th of a second – a less tiny fraction of a second. You can leave the shutter open longer – and some types of low light photography involve opening the shutter for many seconds at a time – but this is uncommon.

The longer the shutter is open, the more light is allowed to come in. So, if you pick a slow shutter speed (like 1/30th of a second), you will let in more light than a quick shutter speed (like 1/500th of a second).

How Else Does Shutter Speed Effect an Image?

As with other camera settings, there is a trade off. So read the next post to find out how else the shutter speed will impact your image.