Camera 101

Balancing Aperture, Exposure and ISO

How does your camera use light to make pictures?

This is your camera. It wants to give you the best picture possible, but it needs your help. Your camera really only cares about one thing when it comes to your picture: light.

In this respect, your camera actually works like a funnel.

Here are two funnels catching water.

Both funnels have the same sized opening at the top, but the funnel on the left has a bigger opening on the bottom than the funnel on the right.

Consequently, given a fixed amount of time, the funnel on the left will let much more water pass through than the funnel on the right.

Thus, if we want to change the amount of water that flows through a funnel, we can adjust either the length of time that the water flows through a funnel, and/or we can adjust the size of the opening at the bottom of the funnel.

Your camera uses a similar framework to catch light. Light bounces off a subject and into the lens of your camera.

Light passes through your camera's lens, and then through a shutter that opens and closes, and then onto an electronic sensor,

The shutter operates in two important ways. First, it can change how far it opens to let light pass through. This opening is called the aperture. It can open small amount to let just a drizzle of light through, or it can open all the way to let a flood through. This is measured in f-stops, and I will refer to this setting as Aperture.

Second, it can change how long it stays open. For instance, it can stay open 30 second to capture time passing (for instance, when photographing a waterfall or star trails), or it can stay open for 1/3000 second to capture literally a split second (for instance, when photographing a bird in flight or a runner). This is measured in fractions of seconds, and I will refer to this as Shutter Speed.

As you can see, this function of the shutter is exactly like the funnel.
But what is the impact of shutter speed and aperture on our composition?

Let's look at Shutter Speed first. On the left, we captured the runner with our aperture open only 1/3000 of a second. Our shutter speed held the aperture open for 1/3000th of a second. As a result, our runner is in sharp focus, and frozen in time. On the right, we captured the runner with our aperture open for a full half second. The result is a blurred runner, valuing movement over detail.

1 Second Exposure

1/80 Second Exposure

There are many instances when you may want to control exposure speed. Above are two examples of catching the surf coming in. The crop of the picture on the left captures the sweeping movement of the waves, while the crop of the picture on the right focuses attention on the textures and subsequent reflections in the water.

1/2000 Second Exposure

1/640 Second Exposure

The picture on the left was taken to freeze the moment when the bears faced off with the salmon. In the picture on the right, however, there is no movement to catch, so a slower shutter speed worked great.

Now let's look at Aperture. When we adjust Aperture, we change the size of the opening through which light passes. This has two important effects. First, the larger the opening, the more light comes in. The more light comes in, the less time the shutter needs to remain open to capture the same picture.

Second, the size of the opening impacts the range of focus within an image,

Let's think about this scene. The photographer is taking a picture of a tree, a barn and the mountains behind.

The photographer may want clear detail on as much of the scene as possible. For instance, they may prefer that the tree, barn and mountains are all in sharp focus. The picture below shows an example of this. To achieve this result, the Aperture was set to f/11. This approach is most often used in landscape photographs where we want to show detail in the entire scene.

f/11

Here the photographer wants to keep the tree and barn in focus, but wants to blur the background to bring greater emphasis to the foreground elements. The picture below was shot using f/8.

f/8

This time, the photographer wants to capture just the tree in focus, with the barn and mountains blurred. As seen in the example below, this results in the foreground standing out in the image, separating more from the background. This method is often used in wildlife and flower pictures to avoid the subjects blending into the background.

f/2.8

To make it all just a bit more complicated, let's throw in ISO.

If we pour water through our funnel onto a thick sponge, it will take quite a bit of water to fully saturate the sponge. But if we pour water through our funnel onto a thin slice of paper, we will saturate the paper very quickly. Your camera's sensor has the ability to be a sponge or piece of paper (or anywhere in between).

That is to say that your sensor can adjust itself to need MORE light to capture an image, or to need LESS light to capture an image.

So why would your camera ever choose to need MORE light?

Well, like most things in life, there's a trade off. ISO stands for International Standards Organization, and it goes back to when cameras used film instead of sensors. Way back, when I wanted a film that would need LESS light to capture an image (for instance, on a cloudy day, or when I was photographing fast action), I purchased 400 ISO film. When I wanted a film that needed MORE light (for instance, on a brght sunny day), I purchased 100 ISO film. Today's cameras have adopted the same sensitivity scale for their sensors.

ISO 3600

The main trade off when using higher ISO settings is noise. Noisy images are grainy, with speckles of lighter or darker tones scattered throughout the picture. Sometimes this is desirable, but often it is not. The picture on the left is a bit grainier than the picture below.

ISO 220

Today's camera produce better results at higher ISO's than yesterday's film. And today's editing software (especially using AI) can reduce noise effectively. Still, it's usually better to capture images with the lowest ISO possible.

Now let's talk about how these three functions interact on your camera.

Essentially, we are wanting to control three functions. (1) How long does the shutter stay open? (2) How wide is the shutter open? and (3) How much light does your camera need to take a shot (ISO)?

You can set each of these independently or in combination. The control mechanisms for setting them vary considerably from camera to camera. Some cameras access these features conveniently through a physical knob or button on the top of your camera, and some require you to go into the menu settings. Check your instruction manual for further details.

When we use these settings in COMBINATION, we have much more power and efficiency in taking our photographs.

Remember, our three main functions are APERTURE, SHUTTER SPEED and ISO.

For each of these, we have three options:

The photographer can manually adjust the setting
The photographer can lock one setting at a specific value, and/or
The photographer can allow the camera to automatically adjust the setting

f/5.6, 1/800 second, ISO 450

In some instances, we care very much about aperture, but not so much about shutter speed. For instance, here is a picture of a sunflower on a sunny day. In this scene, we have plenty of light, so we don't need to force a longer shutter speed, and we don't need to pick a higher ISO. The one function we do care about is Aperture, since we want the sunflower to stand out against the background. Our camera gives us the ability to make these adjustments quickly using the "Aperture Priority Mode." Using this feature (which is generally controled from a knob on the top of the camera), we will manually set the aperture, and lock down the ISO (in this case, at ISO 100). The camera will then adjust the shutter speed automatically to capture the correct amount of light.

f/22, 1/4 second, ISO 50

In other instances, we care about shutter speed, but not Aperture. In this picture, most of the elements are at a relatively constant distance from the photographer, so aperture is not a big consideration. At the same time, I was able to use a tripod, so there is no need to adjust ISO to force a shorter exposure. But what I did want in composing this picture was fuzzy water. I hoped to get an ethereal look from the waterfall, and that comes from a longer exposure. Consequently, I set the shutter speed to a bit longer, kept the ISO locked at 50, and let the camera pick the apeture.

f5.6, 1/3200 second, ISO 800

When shooting wildlife, I am very concerned with both Aperture (I want the animal to pop out against the background) and Shutter Speed (especially if the animal is moving). But I am fine with a bit more noise in the picture, since I can edit it out in Photoshop later. So in this picture, I set the shutter speed and the Aperture, and then the camera automatically adjusted the ISO.

Now let's look at some specific photos where I had to make careful decisions about Aperture, Shutter Speed and ISO.

1/3200 second, f/5.6, ISO 2200

This picture was shot on an overcast day, which means that I had very little reflective light to work with. The geese were in motion, and I was tracking them with my lens as they flew from right to left in front of me. As a result of these two conditions, I needed a fast shutter speed to freeze them in flight. This picture was taken at 1/3200 of a second. I also wanted to make sure that the brown geeze stood out against the brown background, so I set my aperture to f/5.6. What did this do to my ISO, which I left on Auto? It bumped the ISO all the way up to 2200, which resulted in significant noise in the background. I could go into Photoshop to correct this noise, or I could have shot at a slightly slower shutter speed to reduce the noise.

This picture was taken on a sunny day, so I had more light to work with. However, I was still concerned with freezing the movement, especially since the crane was much closer to me, and moving faster relative to my lens tracking it. I set my shutter speed to 1/2500 of a second. In this case, I did not need to worry about blurring the background, since there is none. However, on that day I was also taking pictures of cranes closer to the ground, so I had my aperture set at f/5.6, which was a low as my lens would go. With my ISO set to Auto, my camera then set my ISO to 160, which creates a nice clean noise-free image. I also de-noised the image a bit in Photoshop.

Comparing this picture to the one above, we see similar shutter speeds and aperture, but very different ISO settings. What made the difference? Sunlight. The first picture was shot in low light due to the high clouds, while the second was shot in direct sun. As a result, the camera needed more time, light or sensitivity to properly expose the scene. Since I locked down the time (shutter speed) and light (aperture), it was left with only the option of adjusting sensitivity (ISO).

1/2500 second, f/5.6, ISO 160

1/1600 second, f/4, ISO 100

This picture was taken at the fabulous Petrified Forest National Park in Arizona. The sunlight was brutally direct and harsh. I was shooting at midday (rarely a good decision for landscape photography) and there was not a cloud in the sky. But this is often the case for me, since as an amateur I usually shoot when I have the chance, not when the conditions are best. So, given the bad lighting, how did I make the most of the scene? Well, in these conditions, it's easy for a scene to lack any sense of depth. Since there are few shadows to help provide a sense of three dimensions, I needed to make the petrified log stand out against the foreground and the background, which means I needed a large aperture (low f/stop). I knew I had plenty of light to work with, so I set my ISO to 100. I could have set it even lower, but I stuck with 100. I chose Aperture Priority Mode, set my aperture to f/4, locked down my ISO, and then let my camera pick the shutter speed. I knew it would be a fast shutter speed, given the excess of reflective light, so I did not worry about using a tripod.

3 seconds, f/11, ISO 400

This image was taken on the same roadtrip, this time at one of the beautiful slot canyons near Page, Arizona. But the conditions were markedly different. While the sun was shining bright, and I was out at midday (just like at Petrified Forest), I was now shooting in a slot canyon with high walls and almost no direct sunlight. So what did I hope to get from this scene? I certainly wanted to capture as much of the scene in focus as possible, including the canyon wall nearest me and the wall farthest from me. So I wanted a small aperture (high f/stop). I also wanted as little noise as possible, so I locked in a low ISO (400 in this case). But I had a tripod with me, and a remote shutter release on my camera for stability, so I did not care as much about shutter speed. So, I set my camera to Aperture Priority mode, selected f/11, and then let the camera select the shutter speed of 3 full seconds.

So why did I lock in my ISO at 400 instead of 100, which would have created even less noise? It's all about tradeoff. If I had locked in at 100, my shutter speed would have been MUCH longer. As a result, that would have impeded other people in the canyon trying to get by me, and I would have had less time to explore and take pictures at other points in the canyon. So 400 was a good compromise for me.

1/320 second, f/8, ISO 100

When I shot this rose after a light rain at the Albuquerque Botanical Gardens, I knew I wanted to capture both depth and detail. I wanted the water drops on the rose and the leaves nearest the rose to really pop out. But I wanted the leaves in the background to blur out, ensuring more attention is paid to the rose. So I use Aperture Priority Mode, setting my aperture to the nice midrange aperture of f/8. I wanted to ensure very little noise and nice rich colors, so I locked my ISO down at 100. And since I was using a tripod, I let my camera pick the shutter speed of 1/320 second.

This scene is very different, but it involves almost identical decisions and settings. I wanted plenty of focal range so that the small pool in the foreground and the tree further back would both be in focus. I wanted rich colors and little noise, so I locked down the ISO to 100. And again in Aperture Priority Mode, I put the camera on a tripod, and let the camera pick its own shutter speed of 1/125 second. Different scene, same goals, nearly identical settings.

1/125 second, f/9, ISO 100

What are some circumstances when aperture, shutter speed and ISO decisions become crucial?

1/125 second, f/3.8, ISO 100

1 second, f/10, ISO 100

The Forest

Forest scenes are notoriously difficult to capture. When we are walking through forests, the trees seem so distinct from each other, and the depth of the scene is obvious. But when take a picture among the trees, the camera flattens the scene, and the trees just seem to meld into each other in a cacophony of branches and shadows. For me, the absolute best weather to photograph a forest is fog. Fog in a forest creates depth, with the closer trees being darker and more defined, and the further trees being lighter and fuzzier. The amount of fog can vary this affect. Both of these photos were taken with a tripod in order to allow for slower shutter speeds. Both were shot at ISO 100 to provide the best color and clarity possible. But the fog in the left picture was thinner than the fog on the right. Consequently, I used a larger aperture (lower f/stop) in the left image in order to allow blur the pictures in the distance a bit more. With the thick fog on the right, I did not need the extra blur, so I picked a high ISO in order to capture as much focus throughout the image as possible. Fog is not always available, so the second best weather for forest pictures is high cloud cover, when there is still enough light to capture the scene, but not so much as to cause harsh shadows. On overcast days, using a larger aperture (lower f/stop) is a great choice.

1/8000 second, f/11, ISO 2500

2 seconds, f/10, ISO 100

The Coast

These two scenes are similar. The lighting conditions were significantly different, with the left picture taken on a cloudy day, and the right picture taken on a sunny day. But despite their similar compositions, my intentions were very different. With the picture on the left, I wanted to capture the power of the waves, freezing their motion to illustrate impact. With the picture on the right, I wanted to emphasize the gentle nature of the tide flowing back and forth over the solid rocks. For the left picture, since it was an overcast day and I was without tripod, I knew I would need a higher ISO, so I locked it in at 2500. I also wanted to capture as much of the scene in focus as possible, including the waves in the background and the receeding water on the rocks in the foreground, so I went with a small aperture (high f/stop setting). Since freezing movement was my intent, my most important consideration was shutter speed, which I set at 1/8000 second. For th epicture on the right, I knew I wanted ethereal fuzzy water contrasted against the sharply focused rocks. So, I pulled out my tripod, and shot for two full seconds. This blurred the waves, which in turn emphasized the sharp focus of the rocks. I locked the ISO at 100 since I was using the tripod.

1/2000 second, f/8, ISO 400

1/3200 second, f/5.6, ISO 2500

Wildlife

Shutter speed often takes center stage when shooting moving wildlife. Aperture is more important when shooting still animals in scenes where they are naturally camouflaged. With the bear picture on the left, I knew I needed to capture fish jumping, and that mandated a fast shutter speed. Since I did not know where the fish would jump relative to my lens (farther away or closer), I also preferred a forgiving focal range. I set the ISO to Auto, and let the camera adjust accordingly.

With the picture on the right, the hawk was hidden among brown branches, so I needed a narrow focal range to make sure the bird popped out. I chose f/5.6, as it was the largest aperture (smallest f/stop) available to that lens.

Notice how the shutter speed for the stationary hawk picture is actually faster than the speed for the jumping salmon picture. This was actually a mistake on my part. Since I was using a tripod, and since the hawk was not moving, I should have shot this at a lower shutter speed. Even though this picture was taken near sunset, I had more freedom to drop my shutter speed than I did.

If this is Too Much Information, no worries. Your camera manufacturer has you covered.

I have been using aperture, shutter speed and ISO for nearly three decades, and I have still not mastered them. Your camera manufacturer knows that most people just want to take a good picture, and don't want to slog through instruction manuals to exert the kind of control described above. So they have created shooting modes or scene modes. These are pre-set shortcuts based on specific shooting conditions.

Different cameras have different scene modes, and often have different names for each of their scene modes. Sometimes you select the mode with a dial or knob on the top of your camera, and sometimes you select them through the menu system on the LCD screen on the back of your camera. Since cameras vary widely on this scene modes, I will just be covering the main concepts here. Be sure to read your camera's online instruction manual for greater detail (the manual shipped with your camera is probably not as comprehensive as the online version).

Fully Auto Mode

In Auto mode, your camera makes nearly every decision other than where to point the camera and when to push the button. Based on the scene you are photographing, it will set your ISO, your Aperture and your shutter speed. In addition, it may also set your focus point (where your camera focuses), your metering mode (which parts of your image are dark or light), and whether to use the flash.

As we have learned, different scenes require different settings. So how does your camera know what kind of picture you want to take? Well, in short, it guesses. It looks at various elements to the scene, for instance: How far are you zoomed in or out? Are there people in your scene? How much light does it have to work with? Are some elements of the scene moving quickly? Based on those and other questions, it creates a best guess for what kind of picture you are taking, and then adjusts the exposure settings (and others) to fit.

Is your camera a good guesser? Probably, but it's not perfect. So the odds are good that you will get a picture that you will get a shot you like, but maybe not the shot you intended.

I don't use Auto often, but when I just need to take a picture fast, that's the setting I turn to.

Sport Mode prioritizes
SHUTTER SPEED

Sport Mode

Since the Fully Auto mode may not recognize that you want to take a picture of a runner, or capture the crashing surf, you may be able to tell your camera to adjust for those situations. When you select sport mode, your camera will prioritize shutter speed, reducing the time needed to take your picture as much as the light will allow, It will likely also increase your ISO speed so that it needs less light to capture the scene, and can thus shoot the scene faster. Aperture may be set as small (high f/stop) as possible in order to maximize the focal range for a moving object. How much these three settings are adjusted, and in what order they are prioritized, will depend on your camera's firmware. So it's always good to experiment when you first get your camera.

Portrait Mode

Portraits emphasize individual people (and sometimes animals). Sometimes portrait photos are taken in a very intentional place to show more of a person's personality or vocation. These are sometimes called environmental portraits. For instance, you may want to photograph a chef in the kitchen, or an artist in their studio. In these cases, it's important to make sure the background is understandable to the viewer, often meaning it is in sharp focus. Environmental portraits are tricky business, since it's easy to clutter a portrait with background elements if you're not careful. So camera manufacturers know that environmental portraits are usually shot by professionals who are not using a scene mode on their camera, but are instead using the manual controls.

Most of the rest of us take portrait photos where the background elements are not key players in the image. We do not usually want the background to conflict with the main subject of the portrait. Indeed, we would often prefer the background is blurry in order to make the subject pop out in the photo. This is what portrait mode is designed to do. In portrait mode, Aperture is prioritized. Aperture is usually wide open (low f/stop), reducing your focal range. Your camera may also elect to turn off the flash, since camera flashes in low lighting conditions tend to flatten the image. Or conversely if your subject is backlit, it may elect to turn on the flash in bright lighting conditions (this is called "fill flash," which is a fascinating topic for another day). Your camera will likely reduce the shutter speed as much as possible, assuming that you are not using a tripod. ISO will likely be the feature that is most variable in Portrait Mode.

Portrait Mode prioritizes
WIDE OPEN APERTURE

Landscape Mode prioritizes
NARROW APERTURE

Landscape Mode

Most landscape pictures are designed to showcase an entire scene. Indeed, even professional photographers create these images with nearly every element in focus, from the nearest rock to the farthest mountain. Sometimes they make exceptions if they want the foreground element to stand out, but usually they are shooting at a very narrow aperture (high f/stop). Your camera will do the same thing in landscape mode. It will prioritize a high f/stop, and try to shoot the scene as quickly as needed. Again, it will assume you are not using a tripod, and will set the shutter speed accordingly. It will adjust the ISO to capture enough light.

Other Modes

There are other modes which sometimes make an appearance on your camera.

Two of these deal with the amount of light your camera thinks it needs to shoot any picture. For this example, let's strip away color from your image. On a bright sunny day, the number of bright parts (pixels) of your picture should roughly balance with the number of the dark pixels. This is called light metering, and your camera does it for you using the three main features (aperture, shutter speed and ISO). The exception to this is full-manual-mode, when you do your own light metering. So on that bright sunny day, your image averages the bright and dark pixels to a nice neutral gray. Now let's think about a night scene. At night, there are far more dark pixels than light pixels. If you camera were to average them out to a neutral gray, the resulting image would be MUCH lighter than you originally see it. So when turn on Night Mode, your camera knows the scene is SUPPOSED TO BE darker than average, and adjusts accordingly. On the other hand, you may be taking a picture of a snowy scene during daylight. In this situation, the scene is supposed to lighter than average, so your camera meters the light accordingly.

Other common scene modes include Macro (which allows you to focus very close on your subject), and Sunrise/Sunset modes (which will emphasize the reds in your image).

Here are some great external websites that provide additional detail:

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