Basic Photo Tips: Aperture, Shutter Speed, and ISO

Just as it was 100 years ago and just as it is today, every camera—be it film or digital—is nothing more than a lightproof box with a lens at one end and light sensitive film or a digital sensor at the other end. It is of course light that enters through a ‘hole’ in the lens (the aperture), and after a certain amount of time (determined by shutter speed) an image will be recorded (on film or digital media). This recorded image has been called—since day one—an exposure, and it still is.

Sometimes, the word exposure refers to a finished slide or print: “That’s a nice exposure!” At other times, it refers to the film or digital card: “I’ve only got a few exposures left.” But more often than not, the word exposure refers to the amount, and act, of light falling on photosensitive material (either the film or digital sensor). And in this context, it comes up most often as part of a question—a question I’ve heard more often than any other: “What should my exposure be?” And my answer is always the same: “Your exposure should be correct!”

Although my answer appears to be flippant, it really is the answer. A correct exposure really is what every amateur and professional alike hopes to accomplish with either his or her camera. Up until about 1975, before many auto exposure cameras arrived on the scene, everyphotographer had to choose both an aperture and shutter speed that, when correct, would record a correct exposure. The choices in aperture and shutter speed were directly influenced by the film’s ISO (speed or sensitivity to light). Most photographers’ exposures would be based on the available natural light. And when the available light wasn’t enough, they’d resort to using flash or a tripod.

The Do-it-all Setting

Today, most cameras, either film or digital, are equipped with so much automation they promise to do it all for you, allowing photographers to concentrate solely on what they wish to capture. “Just keep this dial here set to P and fire away! The camera will do everything else,” says the enthusiastic salesman at the camera shop. Oh, if that were only true! Chances are that most—if not all—of you who are reading this article have a do-it-all-for-you camera, yet you still find yourself befuddled, confused, and frustrated by exposure. Why is that? It’s because your do-it-all-for-you camera is not living up to that promise, and/or you have finally reached the point at which you want to consistently record creatively correct exposures.

The do-it-all camera often falls short of its promise, yielding disappointing results. Use your camera’s manual settings, or at the very least, know how light and shadow interact on film or digital media so that you can be assured of getting it right even when you are in auto exposure mode.

Setting and Using Your Camera on Manual Exposure

I know of no other way to consistently make correct exposures than to learn how to shoot a fully manual exposure. Once you’ve learned how to shoot in manual exposure mode (it’s really terribly easy), you’ll better understand the outcome of your exposures when you choose to shoot in semi- or full auto exposure mode.

With your camera and lens in front of you, set your camera dial to M for manual. (If you’re unsure on how to set your camera to manual exposure mode, read the camera manual!) Grab your kid or a friend to use as your subject and go to a shady part of your yard or a neighborhood park, or if it’s an overcast day, anywhere in the yard or park will do. Regardless of your camera, and regardless of what lens you’re using, set your camera dial to M Mode and the lens opening to the number 5.6 (f/5.6). Place your subject up against the house or some six- to eight-foot shrubbery. Now, look through the viewfinder and focus on your subject. Adjust your shutter speed until the camera’s light meter indicates a “correct” exposure in your viewfinder and take the photograph. You’ve just made a manual correct exposure!

Operating in manual exposure mode is empowering, so make a note of this memorable day.

The Photographic Triangle

This does not mean that I want you to forever leave your camera’s aperture at f/5.6 and simply adjust your shutter speed for the light falling on your subject until the viewfinder indicates a correct exposure. Before you forge ahead with your newfound ease in setting a manual exposure, you need to learn some basic concepts about exposure.

A correct exposure is a simple combination of three important factors: aperture, shutter speed, and ISO. Since the beginning of photography, these same three factors have always been at the heart of every exposure, whether that exposure was correct or not, and they still are today—even if you’re using a digital camera. I refer to them as the photographic triangle.

Locate the button, wheel, or dial on your camera or lens that controls the aperture. If you’re using an older camera and lens, the aperture control is a ring that you turn on the lens itself. Whether you push buttons, turn a wheel, or rotate a ring on the lens, you’ll see a series of numbers coming up in the viewfinder or on the lens itself. Of all of the numbers you’ll see, take note of 4, 5.6, 8, 11, 16, and maybe even a 22. (If you’re shooting with a fixed-zoom-lens digital camera, you may find that your apertures don’t go past 8 or maybe 11). Each one of these numbers corresponds to a specific opening in your lens and these openings are called f-stops. In photographic terms, the 4 is called f/4, the 5.6 is f/5.6, and so on. The primary function of these lens openings is to control the volume of light that reaches the film or digital media during an exposure. The smaller the f-stop number, the larger the lens opening; the larger the f-stop, the smaller the lens opening.

For the technical minded out there, an f-stop is a fraction that indicates the diameter of the aperture. The f stands for the focal length of the lens, the slash (/) means divided by, and the number represents the stop in use. For example, if you were shooting with a 50mm lens set at an aperture of f/1.4, the diameter of the actual lens opening would be 35.7mm. Here, 50 (lens focal length) divided by 1.4 (stop) equals 35.7 (diameter of lens opening). It makes my head spin just thinking about all that. Thank goodness this has very little, if anything, to do with achieving a correct exposure.

Aperture

Interestingly enough, each time you descend from one aperture opening to the next, or stop down, such as from f/4 to f/5.6, the amount of light passing through the lens is cut in half. Likewise, if you change from an aperture opening of f/11 to f/8, the volume of light entering the lens doubles. Each halving or doubling of light is referred to as a full stop. This is important to note since many cameras today offer not only full stops, but also the ability to set the aperture to one-third stops, i.e. 
f/4
, f/4.5, f/5, f/5.6, f/6.3, f/7.1, f/8, f/9, f/10, f/11, and so on. (The underlined numbers represent the original, basic stops while the others are the newer one-third options sometimes available).

Shutter Speed

Now let’s turn to shutter speed. Depending on the make and model, your camera may offer shutter speeds from a blazingly fast 1/8000s all the way down to 30 seconds. The shutter speed controls the amount of time that the volume of light coming through the lens (determined by the aperture) is allowed to stay on the film or digital media in the camera. The same halving and doubling principle that applies to aperture also applies to shutter speed.

Let me explain. Set the shutter speed control on your camera to 500. This number denotes a fraction—500 represents 1/500 second. Now change from 500 to 250; again, this represents 1/250s. From 1/250s you go to 1/125, 1/60, 1/30, 1/15, and so on. Whether you change from 1/30s to 1/60s (decreasing the time the light stays on the film/digital media) or from 1/60s to 1/30s (increasing the time the light stays on the film/digital media), you’ve shifted a full stop. Again this is important to note since many cameras today also offer the ability to set the shutter speed to one-third stops: 
1/500s
, 1/400s, 1/320s, 1/250s, 1/200s, 1/160s,1/125s, 1/100s, 1/80s, 1/60s, and so on. (Again, the underlined numbers represent the original, basic stops while the others are the newer one-third options sometimes available). Cameras that offer one-third stops reflect the camera industry’s attempts to make it easier for you to achieve “perfect” exposures. But as you’ll learn later on, it’s rare that one always wants a perfect exposure.

ISO

The final leg of the triangle is ISO. Whether you shoot with film or use a digital camera, your choice of ISO has a direct impact on the combination of apertures and shutter speeds you can use.. To better understand the effect of ISO on exposure, think of the ISO as a worker bee. If my camera is set for ISO 100, I have, in effect, 100 worker bees; and if your camera is set for ISO 200, you have 200 worker bees. The job of these worker bees is to gather the light that comes through the lens and make an image. If both of us set our lenses at the same aperture of f/5.6—meaning that the same volume of light will be coming through our lenses—who will record the image the quickest, you or me? You will, since you have twice as many worker bees at ISO 200than I do at ISO 100.

ISO and Shutter Speed

How does this relate to shutter speed? Let’s assume the photo in question is of a lone flower taken on an overcast day. Remember that your camera is set to ISO 200 and mine to ISO 100, both with an aperture of f/5.6. So, when you adjust your shutter speed for a correct exposure, 1/250s is indicated as “correct,” but when I adjust my shutter speed for a correct exposure, 1/125s—a longer exposure—is indicated. This is because your 200 worker bees need only half as much time as my 100 worker bees to make the image.

Understanding Exposure

Since this is such an important part of understanding exposure, I want you to pause in your reading for a moment and get out your camera, as well as a pen and paper. Set the film speed dial to ISO 200; (If you are a film shooter, do this even if you have a roll of film in your film camera that is not ISO 200, but don’t forget to set the ISOback to the correct number when we’re done here.) Now, set your aperture opening to f/8, and with the camera pointed at something that’s well illuminated, adjust your shutter speed until a correct exposure is indicated in the viewfinder. (If you want, you can leave the camera in the automatic aperture-priority mode for this exercise, too). Write down that shutter speed. Then, change your film speed again, this time to ISO 400, leaving the aperture at f/8, and once again point the camera at the same subject. Whether you’re in manual mode or auto-aperture-priority mode, you’ll see that your light meter is indicating a different shutter speed for a correct exposure. Once again, write down this shutter speed. And finally, change the ISO to 800, and repeat the steps above.

What have you noticed? When you change from ISO 100 to ISO 200 your shutter speed changed: from 1/125s to 1/250s or perhaps something like from 1/160s to 1/320s. These shutter speeds are examples, of course, and not knowing what your subject was, it’s difficult at best to determine your actual shutter speeds, but one thing is certain: each shutter speed is close to if not exactly half as much as the one before it.

When you increase the number of worker bees (the ISO) from 100 to 200, you cut the time necessary to get the job done in half. (If only the real world worked like that!) This is what your shutter speed was telling you: Going from 1/125s to 1/250s is half as long an exposure time. When you set the ISO to 400, you went from 1/125s—passing by 1/250s—and ended up at 1/500s. Just as each halving of the shutter speed is called 1 stop, each change from ISO 100 toISO 200 to ISO 400 is considered a 1-stop increase (an increase of worker bees).

You can do this same exercise just as easily by leaving the shutter speed constant, for instance at 1/125s, and adjusting the aperture until a correct exposure is indicated in the viewfinder; or, if you choose to stay in auto exposure mode, select shutter-priority, set a shutter speed of 1/125s, and the camera will set the correct aperture for you.

Now that you are armed with this simple yet invaluable information, let’s put it towards some truly creative uses! The next article will explain in detail how to correctly expose your photographs.

Shutter and Aperture 

Controlling Exposure
In order for an image to be captured on film, it must be exposed to light. The camera has two settings that control light, and they work very similar to the human eye.

The Shutter:

The shutter blocks all light from exposing the film UNTIL you press the button. Then it quickly opens and closes, giving the film a brief flash of light. You can control the length of time the shutter remains open by setting the SHUTTER SPEED. Longer shutter speeds = more lightshorter shutter speeds = less light «« Canon Rebel 35mm shutter in closed position.

The Aperture: 

Before light reaches film, it must pass through an opening called an "Aperture". The aperture is like a pupil. You can control the aperture by setting the "Aperture Opening", also known as an F-Stop. Smaller F-stops numbers = larger openings larger openings = more light

brightness is reduced as light passes through an aperture.

Shutter Speed: 
Determines HOW LONG the shutter stays open.

The longer exposures ( like 1 second ) give much more light to the film than a 1/1000 of a second exposure. So even though the number may look bigger, don't be deceived! Examples: A half second exposure is ONE STOP darker than a one second exposure. A 1/125 exposure is TWO STOPS brighter than a 1/500 exposure. A 1/1000 exposure is THREE STOPS darker than a 1/125 exposure. « Every step in this table represents a ONE STOP change in light.

Aperture Settings (F-Stops):

Like the pupil in a human eye, the aperture on a camera controls light. It does so by closing up to restrict light, and opening up to let it through. Examples: moving from f16 to f8 is: TWO STOPS brighter. moving from f5.6 to f8 is: ONE STOP darker moving from f4 to f2.8 is: ONE STOP brighter Every step in this table » represents a ONE STOP change in light.

Balancing Shutter and Aperture:
Exposure is about different combinations of shutter and f-stop settings. These combinations can drastically affect the finished picture. For example, the following three pictures have been given an equal amount of light, but the f-stop and shutter combinations make each one unique.

Why is the background all blurred in the right picture, and sharpest in the left ? Because if the exposure is made with a wide aperture ( like f2.8 ), then objects farther away from the subject are thrown farther out of focus. This effect is referred to as "depth of field"

So.. if the aperture is small (like f22) then objects in the background (and foreground ) will appear sharper. However, since more light was required to make the exposure on the left ( 1/4 Second ) the subjects became blurred from MOTION. At 1/250th of a second, the shutter is fast enough to freeze motion.

Take a stop, Give a stop.
Since f-stop and shutter are both measured in stops, keeping balance is easy. If you take away 2 stops from the aperture, you can give 2 stops back with the shutter and end up with the same exposure level.

Shutter Speeds and Apertures

Depth of Field explained. Panning at slow shutter speeds. Blurred pictures. Selective focus. Blur the background. Tricks and tips for working with shutter speeds and apertures.

Shutter Speed

Although, as discussed in exposure, the shutter speeds and apertures are interchangeable as far as exposure is concerned, they each have their own unique effect on the picture. Let's take a look at shutter speeds first as their effect is easily understood. We'll look at apertures further down the page.

The shorter the time that the shutter is open the sharper the photo will be.

If you are photographing fast moving objects such as cars or people running you need to select fast shutter speeds to capture the sharpest picture you can. One exception to this is when you are panning the camera with the subject, the object of the exercise here is to render the subject sharply and blur the background, so a careful selection of the right shutter speed to do both is necessary. I often find that a little blur in the right places on a picture gives a greater sense of movement than if everything is pin sharp. This blur, however, must be in the right places, normally we want to see the head and torso rendered sharply but, if the feet and hands are blurred, it can often be a good thing. Blurring the background can also get you out of trouble when there is a lot of clutter that will detract from the main subject. Getting the shutter speed right to render the correct balance of sharpness and blur on any given subject can really only be determined through trial and error. One of the great advantages of the digital camera with it's instant playback is that this learning process can be a lot shorter than it was before. If you have a zoom facility on your playback of pictures, now is the time to get familiar with it. I had my digital camera for quite a while before I realized that I could review my pictures and zoom in to check the sharpness.

Not only moving objects suffer from too slow a shutter speed. If you are holding the camera in your hand rather than having it mounted on a tripod, you will see the telltale signs of 'camera shake' (i.e. the movement of the camera) at shutter speeds longer than 1/125th of a second. A secure pair of hands will be able to get away with 1/60th or even 1/30th of a second but the camera would be better mounted on a tripod. Once again I will say at this point that the difference between a mistake and an effect is usually the degree. A small amount of blur would be considered a mistake, whereas really blurred streaks of light can be an interesting effect. It's all a question of convincing the viewer that you intended to do it.

Tip - When the shutter speed is important as with moving objects, it's a good idea to set the camera to 'Shutter Speed Priority' mode. This is where you select the shutter speed and the camera selects the appropriate aperture according to the light reading.

Of course, if you are taking photos of static objects like houses with a camera mounted on a sturdy tripod, you can leave the shutter open as long as you want without blurring. An interesting by-product of this, if you get to see really old photos taken in the first part of the 19th century, you will see that there are almost no people in the photos at all. That is because the exposure times were so long that the people had walked through the scene without being rendered. For the same reason the really early pictures, in the time of Niépce, the late 1830's, have almost no shadows because the plates took all day to expose and the sun moved across the sky illuminating the scene from both sides.

Apertures

As well as letting more or less light into the camera the size of the aperture you choose governs the 'Depth of Field'. Depth of field means the amount of the picture, from foreground to background, that is in sharp focus. A smaller aperture will give you a greater depth of field and a larger aperture will give you a more restricted depth of field. This characteristic can be used to good effect in many ways.

If you are photographing vast landscapes on a sunny day, the chances are that everything will be in focus and you will not notice this phenomenon at all. Depth of field, or the lack of it, is much more noticeable when taking close-ups. As I mentioned in the section on moving subjects, it is often desirable to render the background of your picture out of focus. This is easy to achieve by selecting a larger aperture to restrict the depth of field.

Conversely, when photographing very small objects (as in the picture opposite) getting everything in focus can be quite a challenge and may require a very slow shutter speed in order to be able to use the smallest aperture available. The focal length of the lens makes a difference to the depth of field available, the longer the lens the more restricted the depth of field. A wide angle lens will give you almost limitless depth of field.

Tip - If depth of field is important to either make sure everything is in focus or to throw some things out of focus, select the 'Aperture Priority' mode on your camera. In this mode you select the aperture and the camera selects the shutter speed according to the available light.

Tip - If you are shooting in bright light and want to restrict the depth of field, use a neutral density filter in front of the lens to reduce the light entering the lens. These are available in different densities, 2x, 4x, 8x etc. each one cutting the light in half, quarter, eighth etc. In extreme circumstances you can screw a couple of them together. Although they are 'neutral density' filters and should not effect the color balance, if you use two or more together you might need a little color correction at the printing stage.