Aperture and Shutter Priority

The Missing Pages column is a collection of all of the information that should have been included in your camera’s Owner’s Manual—but somehow got left out. This is a hybrid assortment of short articles that delivers the know-how you need to derive the maximum enjoyment—and creative expression—from your equipment.

It’s sort of a juiced-up User Guide for creative people who are not necessarily technical. Each part will teach you how to use one of the camera features or functions that you previously ignored or left set on Auto. And each will include a Creative Project so that you can try some scripted experimentation.

We will explain complex technical subject matter a way that everyone can understand. And if you happen to be a technical expert yourself, we’re including “Nerds Only” sidebars just for you. That way you can dig in deep—or just straddle the edges—of the technological stuff. It’s your decision.

Installment III: Aperture & Shutter Priority

Definition: exposure modes that provide more control than Program AE but less than Manual mode.

Shutter Priority is an auto exposure system in which the camera achieves correct exposure by selecting the aperture after the user has selected the shutter speed.

Conversely, Aperture Priority is an auto exposure system in which the camera achieves correct exposure by selecting the shutter speed after the user has selected the aperture.

Each system has its own set of distinct advantages and disadvantages. But to fully understand Aperture Priority and Shutter Priority you must understand the fundamentals of exposure. Please refer to the preceding segment (Program AE) if you need a quick review.

Today’s digital SLR cameras (and a few high-end compact models like the Canon PowerShot G10) offer both Aperture Priority and Shutter Priority automatic modes in addition to Program AE. There was a time, however, back during the era of Canon AE-1 popularity, that 35mm film cameras offered one autoexposure system or the other. And each method had its own passionate group of proponents—and detractors.

The Canon (Shutter Priority) crowd argued that it was better to set the camera’s shutter speed and allow the camera to respond by setting the appropriate f/stop. They claimed—and rightfully so—that by choosing a fast shutter speed it was easier to control camera shake and to stop subject movement. Minolta, Nikon and Pentax (Aperture Priority) followers insisted that setting the aperture was the preferred procedure because it gave the user full control over the depth-of-field and allowed the user to preselect the optimum aperture for any lens.

Both sides were correct, of course, each in their own way. In retrospect, this issue was one of the most polarizing disputes among camera enthusiasts, no pun intended. One might have expected a different outcome to this hotly debated argument, but the final result was the development of Program cameras that set BOTH the shutter speed and aperture, essentially leaving the user out of the equation almost entirely. Better cameras offered all three: A mode, S mode and Program AE. The Minolta XD-11, which debuted in 1977, was the first camera that could claim “Dual Mode” by offering both A and S modes.

Use Aperture Priority to control the background.

Aperture Priority

Sometimes called “Aperture Preferred” because that term more accurately describes what’s in the user’s mind when they make decisions about the camera settings; and labeled “Av” (Aperture Value) by Canon and others; Aperture Priority allows the user to control depth-of-field (that zone of sharpness that extends in front of and behind the actual point of focus). Because it’s often indicated by an “A” on the control dial, some people mistake the setting for “Automatic.”

Having control over the DOF is very important in more situations than not. When shooting portraits, for example, it’s desirable to force the background to blur by using a large aperture. This effect separates the subject from what’s behind them and gives the appearance of accentuated sharpness. It also allows you to deemphasize distracting backgrounds by making them fuzzy and indistinguishable. Controlling DOF is similarly important when you want a larger zone in focus (greater DOF), such as when shooting close-ups or certain landscape scenes.

Controlling the aperture allows you to select the “sweet f/stop” that delivers the sharpest images. There are rare exceptions, but most lenses perform better when stopped down two or three f/stops. A 50mm f/1.4 Nikkor, for example, will yield better results at f/4 than it will at f/1.4. And contrary to intuitive logic, using an f/stop like f/22 that’s quite small introduces diffraction, which robs the image of sharpness, despite the extended depth-of-field.

Use Shutter Priority (and a high shutter speed) to stop action.

Shutter Priority

Known as “Tv” to Canon (for Time Value), there’s a lot to be said about the efficacy of this system—particularly in light of the fact that all camera makers recognize the detrimental effects of camera shake and are moving toward some sort of Image Stabilization to reduce it.

In S Mode, you set the shutter speed and the camera does the rest. Well, not quite. The argument that the Aperture Preferred crowd often made was this: if you set a shutter speed that’s too high (1/250s indoors, for example) you’re likely to get no picture at all. As a countermeasure, many cameras will warn you and then shift to a slower speed when it’s impossible to achieve correct exposure at the speed you selected. And some will even adjust ISO (although that’s really a case of relinquishing control over the final outcome to the camera and hoping for the best).

Controlling the shutter speed means you can help prevent camera shake and more importantly, freeze subject movement. If you’re shooting a track and field event, for example, or a little league game, you can use a very fast shutter speed to stop motion.

This theory works well indoors, too. For any given lens you should know the minimum shutter speed you can successfully handhold without shake. I call this the “SBA” or “Shake Begins At” shutter speed (ungrammatical but easy to remember). With a 50mm lens equivalent, for example, most people can shoot at 1/60 of a sec or so. General rule of thumb is “1 over the focal length” as in the fraction 1/focal length. So the equivalent to a 135mm lens would require a shutter speed of about 1/125 or higher for safe, jiggle-free results. (Remember that this old rule came to be before digital, so you must account for the lens multiplier when calculating.) In Shutter Priority you can set the camera at your SBA and blaze away with little fear of camera shake.

A Mode allows you to control Depth of Field.

Creative Project

Do you have a favorite lens? One that always seems to yield the sharpest images? With that go-to lens in mind, what range of apertures delivers the absolute best performance? You really need to know. For the sake of having an example, let’s say you’re a Nikon D90 shooter and your favorite lens is the 50mm f/1.4. (Not a bad choice, by the way, in that it translates to a 75mm f/1.4 on your DSLR, which gives you a nearly perfect portrait lens).

Exercise 1

Get out the tripod, find a subject with detailed texture, and set up ten to fifteen feet away. If you can’t think of anything better, aim your camera at a painting that’s hanging on a neutral wall. Shift your camera into Aperture Priority mode and begin shooting at the largest f/stop, working your way down to the smallest. How do the images in the series compare in terms of sharpness?

You may find that your results resemble these: Wide open at f/1.4 you get good results, but stopped down to f/4 or f/4.5 (the half stop between f/4 and f/5.6) the lens really shines. Sharpness remains until around f/16 where diffraction takes over and the results—while still acceptable—are not as biting-sharp as at f/5.6 or f/8.

Exercise 2

For the second exercise, position a human subject five feet from the painting and ten feet from the camera. Repeat the exercise above, keeping the camera focused on the human. This time when you examine the results, closely look at how the subject becomes more separated from the background as depth-of-field decreases.

Exercise 3

Don’t freeze the action all of the time. Movement can add dramatic emphasis to the dynamic flow of a river, for example. You’ll need the tripod again. If you don’t have a gushing waterfall handy, moving traffic (especially at night), frenetic musicians (especially during the wee hours) or typical preschoolers (after a sugary snack) will provide enough subject movement to make this test worthwhile. In S mode, select a very slow shutter speed—one-half second or longer, unless it’s so bright that you’ll overexpose. Make sequential exposures at progressively faster speeds until you reach the speed that completely stops all subject movement. Then compare the results in your favorite image editor.

What about M mode? M stands for Manual, of course. That’s a great Creative Project but that’s for another episode!

For Nerds Only

What’s Pi got to do with f/stops? And why is f/2 twice as big as f/2.8 and four times larger than f/4? Shouldn’t bigger numbers mean bigger apertures?

Shutter speeds are pretty easy to understand. 1/100 of a second is obviously half as long as 1/50 of a second. But when it comes to f/stops nothing seems to make sense. That’s because an f/stop is a fraction. It’s the ratio between the lens’s focal length and the diameter of the active aperture. For example, a 50mm lens that is set at f/2 has an aperture that is 25mm in diameter. Similarly, a 50mm lens that is set at an aperture that is 8.9mm in diameter is said to be set at f/5.6 (i.e., 50/8.9 = 5.6).

Remember high school algebra? I’m sure many photo.net readers will want to jump in here and untangle my amateur math, but here’s what I remember. To calculate the area of a circle one multiplies the radius times the radius times pi. Or in other words, the radius squared multiplied by the constant 3.14159.

If you’re still with me, look at the following table.

For a 50mm lens:

So, it’s (fairly) easy to see why f/2 is about twice as large as f/2.8. The area is about twice as large. As we go down the scale, each increment of one f/stop equals a 2X change in exposure because the area becomes half as large. That is to say, each subsequent f/stop is one-half as large as the preceding f/stop. Half of a half is a quarter, so the difference between f/4 and f/8 is two stops, or 4X.

Why use such a goofy system? Because it can be applied to a lens of any focal length. For the purposes of calculating exposure, a 135mm lens set at f/5.6 delivers exactly the same amount of light as a 300mm lens at f/5.6. Were it not so, it would be virtually impossible to base camera exposure settings on an external handheld light meter.

Wedding Photography:Two “Camps” Of Style And Vision

There was a time when all wedding photography was pretty much the same. Well-trained photographers worked from “shot lists” and used high-end, medium format equipment. They took wedding portraits (many in-studio) whose hallmarks included great color, sharp details, beautiful lighting, and well-posed subjects. Wedding albums were filled with 8x10”, 8x8”, and 5x7” prints of carefully posed images of couples, their families, and the bridal party, all smiling nicely for the camera. These traditional photographers often took charge at the wedding and everything unfolded on their timetable so each shot would be as perfect as possible. The wedding party also spent considerable time posing for photos before, during, and after the event.

© 2010, Tony Hewitt, All Rights Reserved

The less-controlled photojournalism style took hold about 12-15 years ago when photographers such as Denis Reggie and Bambi Cantrell began to photograph weddings like photojournalists, often using 35mm cameras. They captured the event as it unfolded without asking people to pose or stop and smile for the camera. There are no hard and fast rules for “wedding journalism” as it is all about documenting the day in an informal/artistic manner. Wedding journalism—and digital cameras—also opened the door for many more photographers, some as skilled as the traditionalists, some not, which created more competition for photographers, but also more options for the public.

Two Camps?
Today, when describing their photographic style, wedding photographers typically label themselves as either photojournalists or traditionalists. Former newspaper photographers Andrew Niesen and Rachel LaCour Niesen, co-owners of Atlanta-based wedding studio LaCour (www.lacourphoto.com), and creators of ShootQ (www.ShootQ.com), a studio management solution for photographers, made the switch from news journalism to wedding journalism in 2001. Their approach to photographing a wedding is the same as a news event, which is to follow the story as it happens and allow it to unfold before their eyes. The couple document weddings in real time using a hands-off approach, which, Andrew notes, is the closest thing to their training.

Photos © 2010, Tony Hewitt, All Rights Reserved

“We feel the pictures we’re making are really treasured by the families even though [the images] have a very small audience as opposed to magazines. We really feel we are doing something very important for our clients.”

Though the way they earn their living has changed, the Niesens say their photographic style has not, except for some minor tweaking. For instance, they’ve adapted their approach from pure photojournalism—where it’s all about the moment—to photojournalism that’s something their clients want. “With photojournalism,” Rachel explains, “we were capturing top news events and dealing with a wide range of subject matter. We realize that sometimes the more bizarre ‘artistic images’ that we appreciate as photojournalists may not be appreciated by many of our clients.”

© 2010, LaCour, All Rights Reserved

The Niesens originally pursued photojournalism as a career so they could be witnesses on the front lines of history. However, they feel good about trading their front row seat to world history for a smaller one in family history. “In a lot of ways it’s just as powerful and more meaningful work because each family will treasure those photos for generations,” Rachel concludes. “It’s a special feeling to know the pictures we’re making for our clients will be used as a foundation for their family legacy for generations.”

Robert Lino (www.robertlino.com), a portrait and wedding photographer for the past 35 years, believes the more traditional style lost favor when it became overly complicated. There were too many complex backdrops and too much time was spent in the studio away from the wedding. “I believe that’s one reason the photojournalism style became ro popular,” Lino reiterates, “because brides didn’t want to spend the whole night in front of a painted background.”

Lino says his work can be described as formal and elegant, with feeling. “My images are very controlled and very directed in order to look very natural,” Lino explains, who says he developed his style partly through observation.

© 2010, LaCour, All Rights Reserved

“I also learned from the masters and all the photographers who broke the rules; but I gave it my own twist and my own interpretation.

“For many years people hired professional wedding photographers. Now, we’re in an era where anybody can shoot a wedding.” Lino believes taking a little more care with images, such as making sure the couple holds the knife correctly when cutting the cake, and taking a few formal pictures in front of a nice background (not a backdrop, but a pretty window, etc.), would go a long way in getting people to hire professionals instead of having a bunch of people with decent cameras shooting thousands of pictures in the hopes of capturing 20 good ones.

Four Facts About High ISOs

There sure is a lot of talk about high ISOs these days. Some folks even say high-ISO shooting is the new frontier of digital photography. Camera makers seem to be focusing their efforts on producing better, cleaner, less noisy images, and that translates directly into improvements at high ISOs. Here are four facts about high-ISO speeds that may make you a better photographer—especially when working in low light. 

1. High ISOs can have minimal noise.
Sure, back in the film days it was true that working at high ISOs and pushing film processing often translated into so much grain that it became hard to make out details (especially in the shadows) of negatives. But with the advances in noise reduction from today’s digital cameras and RAW converters, higher ISOs produce image quality unparalleled by high ISO films. Not only that, digital high ISOs are so low noise these days that many photographers are putting them to use in ways they never considered before—like nighttime exposures that are short enough to render starry skies without blurring, or photographing in dark interiors without the need for fill flash illumination. Photographers today know they can pull detail out of the darkest of shadows, and much of that is thanks to the same improved signal-to-noise ratio that makes high ISOs so darn attractive.

2. Digital ISOs aren’t contrasty like film.
When working with fast film speeds, photographers often found themselves pushing exposures by underexposing in camera and overdeveloping in the darkroom. While this process did provide higher-working ISOs than the film was rated for, it also introduced some major drags on the image quality—both the grain mentioned previously as well as a whole ton of contrast. So much contrast, in fact, that high-ISO film images could sometimes look like abstract art. Imagine a grainy image with very little detail in the shadows and highlights—and none available to be pulled from the negative. That just doesn’t hold true today when working with RAW files. RAW is especially capable of rendering detail in very dark shadows, and the only processing that eliminates shadow detail comes from underexposed files. If you can overexpose a digital image even slightly, you’ll be amazed at the detail that remains in the dark tones without any contrast gain at all. 

3. High-ISO performance matters even at low ISOs. 
You only shoot at ISO 400 or less, so why should you care about better performance at higher ISOs? Because those low-noise/high-detail qualities are carried across the entire ISO sensitivity range. In layman’s terms, ISO 400 from today’s D3 looks a lot like ISO 100 did in the D1 of yesterday. If you like image quality, you like to see advances in ISO capabilities due to better signal-to-noise ratio. Those gains will show up in your low-ISO images too. So when you hear of new cameras reaching new high-ISO low-noise heights, it’s good news for you too. 

4. Sometimes it’s better to choose a higher ISO even if you don’t have to. 
Generally speaking, this one appears as if it might be awful advice. But let’s say it’s a fairly low-light situation in which you’re working, and you need a fast shutter speed of 1/125th of a second to keep the subject from blurring. The lens only opens to ƒ/4 and you’ve maxed it out, and you’re at ISO 400. Still, you’re just barely getting the correct exposure. One way to ensure you’re getting an even better exposure is to boost the ISO to ISO 800. Why? Because if you capture RAW you’ve got the added benefit of being able to pull extra detail out of shadows from slightly overexposed image files. That can produce an image with more detail across the spectrum from shadows to highlights. As long as highlights aren’t blown out in the capture, an overexposed RAW file will actually produce a higher-quality file after image processing than a “correctly” exposed RAW file would. 

Some might say boosting the ISO offsets any noise gains that come from overexposure, and that could very well be true. But in terms of shadow detail, there’s no doubt: the extra detail that can be pulled from brighter shadows is awesome. This holds especially true in low-key images full of dark tones where you’re more likely to keep from blowing out highlight detail.

White Balance

White balance is an adjustment that accounts for the color temperature of the light in a scene. All light sources emit light at a specific color temperature, which is expressed in Kelvin. As the light travels, it may pass through particles in the atmosphere or a filter on the lens, which filters some of the wavelengths. For example, a sunset is usually around 3000-4000K, while bright, midday sun is about 5000-6500K. The sun is always the sun, so the change in color temperature from midday to sunset is due to the amount of atmosphere and particles like smoke or dust through which the light travels. When we adjust the white balance on the camera, we’re essentially telling the camera to account for the color temperature to make the colors more neutral. Whites will look white, greens will look green, reds will look red. 


Reflective-Style White Balance
If you have a neutral subject like a white piece of paper or a gray building, you can key off of that. In nature photography, however, we seldom have a white sheet of paper in the scene to use as a neutral point, but you can carry something with you and use that to balance the scene.

The WhiBal White Balance card (www.rawworkflow.com) is a neutral gray card that you can use to set white balance in the field or to make adjustments to a file when you process the RAW files (those of us who shot film and used handheld spot meters will find the WhiBal reminiscent of a traditional gray card and it’s used in roughly the same way). The WhiBal is designed for low reflectivity, it’s perfectly gray, and it doesn’t respond to UV light any differently than the visible spectrum. Place the card in the scene and key off of it, or take a picture with the card in the scene (then remove it for your “real” exposures) and use your processing software to get the proper color temperature setting. You then can apply that color temperature to all your other images shot under the same lighting conditions. 

The Datacolor SpyderCube (spyder.datacolor.com) looks like a black-and-white Christmas ornament with a small shiny ball on ht. The cube’s surfaces are white, gray and black, and each surface is spectrally neutral. One face of the SpyderCube has a hole that acts as a black trap to give you a control point for shadow detail. You can use it to set the proper color temperature while you’re shooting, or take a picture, remove the SpyderCube and use the image with the cube to set the color temperature for the series when you’re processing the images in the computer.

Incident TTL-Style White Balance
A different way to get your white balance set is with a device that sits on the front of your lens and lets you auto-white balance off of it. Available in most standard diameters, the Brno baLens (www.hpmarketingcorp.com) simply snaps onto your camera lens, and you can attach a neutral or a warm-colored dome to it to get the results you want. The baLens also can do double duty as a lens cap.

ExpoImaging (www.expoimaging.com) makes a few different on-the,lens-type, white-balance tools. Designed for DSLRs, the ExpoDisc snaps onto your lens with a pressure-release friction mount. Press the button and it pops off, leaving you ready to shoot. The company manufactures the discs to strict tolerances, ensuring 18% transmission and neutrality in the visible spectrum. That neutrality, of course, is critical for getting the most accurate white balance possible. There’s also an ExpoImaging white-balance tool for video, as well as one for point-and-shoot cameras.


Lally Cap Another on-the-lens white-balance tool is the Lally Cap (www.lallyphotography.com). It’s unique as a one-size-fits-all solution that can be used on just about any lens. The fabric “cap” slips over the lens sort of like a small sock, you set the white balance, and then you can just pull it off and stuff it in your pocket.

All of the devices mentioned in this Solutions article can fit into your gear bag and weigh almost nothing. The point is that you should always carry at least one of them in your bag. You’ll be ready with the perfect white-balance tool when the perfect day for shooting comes along.