Booklet Mastering Exposure in Digital Photography Lbv

Mastering Exposure in Digital Photography

LEARN BY VIDEOWO R K S HO P

Presented by Tim Grey

UPGRADE YOUR SKILLS IN A FEW HOURS

THIS FOCUSED WORKSHOP provides over 2 hours of high-quality video aimed at helping photographers understand

the key elements of photographic exposure and how to control them to make better photos. This includes thorough

explanations of camera aperture, shutter speed, and stops, as well as ISO and white balance. Then instructor Tim Grey

turns to the ways that digital photographers can adjust exposure using camera modes and other tools. Tim covers

advanced techniques, including exposure compensation, exposure bracketing, and multiple exposures, and he addresses

adjustments to exposure that can be done with software, after an image is sent from camera to computer.

Table of Contentsis never more than a click away

High-quality downloadable exercise � lesare includedon the DVD

Video player remembers which movie you watched last

Watch-and-Work mode shrinks the video into a small window so you can practice while you learn

Crisp, 1280x720 High-Def video that you can watch in full-screen mode for an exceptionally immersive learning experience

Bookmark your favorite videos

BOOK LEVEL: BeginnerCOMPUTER BOOK SHELF CATEGORY: Digital PhotographySYSTEM REQUIREMENTS: Microsoft Windows XP/Vista/7; Max OS X; Linux.512 MB RAM; Display resolution 1024 x 768 or higher

Peachpit Presswww.peachpit.com

Presenter:Tim GreyThe team at video2brain created and produced this high-quality video training

course. Every year, hundreds of thousands of customers around the world take advan-tage of the unique learning experiences o� ered by video2brain, which are available on DVD-ROM and online at www.video2brain.com.

Expert instructor Tim Grey’s work combines several of his passions: technology, teaching, photography, writing, and travel. He has written more than a dozen books on digital imaging for photographers, including Real World Digital Photography and Take Your Best Shot. In addition to his work with video2brain, Tim teaches through workshops, seminars, and appearances at major events.

0321786939_booklet.indd 1 6/16/11 3:39 PM

Mastering Exposure in Digital Photography

Learn by Videowo r k s ho p

Presented by Tim Grey

Mastering Exposure in Digital Photography: Learn by Videovideo2brain GmbH • Tim Grey

Copyright © 2012 by video2brain GmbH

Peachpit Press1249 Eighth StreetBerkeley, CA 94710510/524-2178 • 510/524-2221 (fax)Find us on the Web at www.peachpit.comTo report errors, please send a note to [email protected] Press is a division of Pearson Education.

Editor: Becca FreedProduction Editor: Cory BormanMedia Producer: Eric GeoffroyProofreader: Susan NasolPackage design: Charlene Charles-WillBook interior design: Danielle Foster

Notice of RightsAll rights reserved. No part of this video training book may be reproduced or transmitted in any form by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. The software and media files on this disc are copyrighted by the authors and Peachpit. You have the non-exclusive right to use these programs and files. You may use them on one computer at a time. You may not transfer the files from one computer to another over a network. You may transfer the files onto a single hard disk so long as you can prove ownership of the original disc. For information on getting permission for reprints and excerpts, contact [email protected].

Notice of LiabilityThe information in this video training book is distributed on an “As Is” basis, without warranty. While every precaution has been taken in the preparation of the video training book, neither the trainers nor video2brain GmbH nor Peachpit shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the instructions contained in this video training book or by the computer software and hardware products described in it.

TrademarksAll rights reserved. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this video training book, and Peachpit was aware of a trademark claim, the designations appear as requested by the owner of the trademark. All other product names and services identified throughout this video training book are used in editorial fashion only and for the benefit of such companies with no intention of infringement of the trademark. No such use, or the use of any trade name, is intended to convey endorsement or other affiliation with this video training book.

ISBN-13: 978-0-321-78693-7 ISBN–10: 0-321-78693-9 9 8 7 6 5 4 3 2 1

Printed and bound in the United States of America

1 GettingStarted

1.1 Welcome

1.2 What Makes a Proper Exposure?

1.3 Equipment Considerations

1.4 RAW vs. JPEG

2 ExposureConcepts

2.1 Aperture and Shutter Speed

2.2 Lens Limitations

2.3 ISO

2.4 Dynamic Range

2.5 Depth of Field

2.6 Understanding Stops

2.7 Reading the Exposure Meter

2.8 Reading a Histogram

2.9 Expose to the Right

2.10 The Role of White Balance

3 ControllingExposure

3.1 Fully Automatic Modes

3.2 Shutter Priority Mode

3.3 Aperture Priority Mode

3.4 The Sunny 16 Rule

3.5 The Gray Card

3.6 Focal Length and Shutter Speed

3.7 Fast Shutter vs. Slow Shutter

3.8 Metering Modes

4 AdvancedExposure

4.1 Exposure Compensation

4.2 Exposure Bracketing

4.3 Manual Exposure Mode

4.4 Half Stop vs. One-Third Stop

4.5 Long Exposures

4.6 Incorporating Flash

4.7 Multiple Exposures

4.8 Capturing HDR Images

MasteringexposureinDigitalphotography:learnbyViDeo iii

DVDContents

5 Post-Processing

5.1 Basic RAW Conversion

5.2 Black Point, White Point, and Midtones

5.3 Advanced Tonal Adjustments with Curves

5.4 Creating a High Key Image

5.5 Blending Multiple Exposures

5.6 Creating an HDR Image

DVDContents

iv DVDContents

DVDContents

Introduction vii

ExposureMath 1

Understanding Exposure Math . . . . . . . . 2

Variables of Exposure . . . . . . . . . . . . . .4

ControllingExposure 13

Blending Aperture and Shutter Speed . . 14

Exposure Compensation . . . . . . . . . . . 22

Glossary 25

MasteringexposureinDigitalphotography:learnbyViDeo v

DVDContentsBookletContents

Introduction

These videos are designed for easy navigation, and you can even bookmark your favorite sections to review again and again. You can also test your-self on what you’ve learned with multiple-choice quizzes. We hope you find this video training and booklet useful and informative and that you are excited about the images you create with your newly acquired skills.

AboutThisBookThe material in this book is aimed at helping you better understand some of the core concepts addressed in the video training. While each video lesson covers a single topic related to photographic exposure, this book strings together many of the most important topics to help you better under-stand the context of the training. In particular, you’ll gain a better sense of some of the math going on behind the scenes for exposure calcula-tions, and how some of the different factors affecting exposure work together.

HowtoUseThisCourseThe video2brain interface is easy to use, but it also has a large number of options. We’ve provided this brief guide to give you a tour of the interface and make sure you don’t miss out on any of its features.

This course comes in a few different flavors. You can run the Mac application (labeled “Start” or “Start.app”) or the Windows application (.exe) file, or you can open start.html in your browser. Most people will use one of the application versions of the course. If you’re working with an operat-ing system that doesn’t support one of these two

WelcometoMastering Exposure in Digital Photography: Learn by VideoConsidering that the moment of exposure truly defines the amount and quality of information contained within the photographic image, it stands to reason that exposure is critical. While today’s digital cameras do a remarkable job of calculating proper exposure under a wide variety of lighting conditions, the photographer must get directly involved in evaluating, and when necessary over-ruling, those calculations in order to produce the very best image.

In this course you’ll learn all the important concepts involved in photographic exposure, but more than that, you’ll see how these concepts are applied in the field. You’ll join instructor Tim Grey as he photographs the Austrian Alps, woods, and rivers, along with downtown scenes and interiors. He’ll walk you through advanced techniques like manual exposure mode, capturing long exposures, exposure bracketing, intentionally blowing out an exposure, and more. Along the way, you’ll see how to avoid common pitfalls and use the available light for best effect.

Back in the studio, you’ll see how you can apply the principles of exposure to post-processing and how you can ensure the very best results in the com-puter after having started with an ideal exposure in the camera. To help bring together what you’ve learned in this course, you’ll also work on some real-world photography projects that blend various aspects of photographic exposure, as well as post-processing in certain cases.

viii introDuCtion

DVDContentsIntroduction

options, such as Linux, the browser version is a great alternative—it works on any browser with a current version of Flash. The main difference be-tween running the course as an application versus opening it in your browser is that the application versions include an option, discussed in more detail later in this guide, called Watch-and-Work mode. Watch-and-Work mode lets you watch the course in a smaller window while you follow along in another application. This option doesn’t exist in the browser version of the course.

Whether you’re using the application or browser version, when you first launch the course, you will see the Welcome screen.

The Welcome Screen

From here, there are a few ways you can proceed:

■■ Click the Play icon in the middle of the screen to watch a video that introduces you to the instructor(s) and gives you an overview of what’s covered in the course.

■■ For onscreen help and a user’s manual, click either the Help item on the menu at the top of your screen or the Need Help item at the bot-tom of the Content panel. You can also access help by pressing F1 on your keyboard.

■■ Entering a word or phrase in the Search field in the upper right of the screen will search the course’s titles and descriptive text to help you find what you’re looking for.

Starting the Course

When you’re ready to dive in, you have several options for how to get started:

■■ To begin at the beginning and play all the way through, click Play All Videos.

■■ To access a list of every video available in the training, click Table of Contents.

■■ To start with Chapter 1 (or any chapter that appeals to you), click the chapter name on the left of your screen.

You can navigate the Table of Contents and Chap-ter views using your mouse, or using the keyboard to arrow up and down, left and right. When you’ve selected a movie, you can press the right arrow to play that movie.

MasteringexposureinDigitalphotography:learnbyViDeo ix

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DVDContents

Navigating Inside a Video

While watching a video, you can use the buttons along the bottom right of your screen to toggle both video smoothing 1 and Full-Screen mode 2 on and off. You can adjust the volume 3 from here as well. You can also click and drag the green line 4 in the timeline at the bottom of the screen to

move around within the video.

When the video ends, click the Next Video button at the top right of the window to go directly to the next lesson. (This will happen automatically if you clicked Play All Chapter Videos to launch the chapter.) At the end of a chapter, this option will change to Next Chapter. You can also click Training Content at any time to leave the player and choose another lesson or click the navigation bar near the top of the screen to access the table of contents.

In the Table of Contents or Chapter view, any time you move your mouse over the name of a chapter or video, text describing the contents of that item will appear on the right side of your screen. This area is known as the Sidebar and is discussed in detail on the next page.

If you click the name of a chapter, you’ll see a list of all the videos in that chapter. Choose the video you want to start with or click Play All Chapter Videos to start with the first video in the chapter and go all the way through.

Keyboard SHorTcuTS for THe Player

■■ Spacebar: Play/pause

■■ right arrow: Jump forward

■■ left arrow: Jump backward

■■ Tab: Show/hide sidebar

■■ b: Add bookmark

■■ M: Show/hide navigation bar

■■ esc: Turn off Full-Screen mode

Introduction

4 3 2 1

MasteringexposureinDigitalphotography:learnbyViDeo xi

Using Bookmarks

It’s easy to create a bookmark in the video to mark where you left off or make note of something you want to refer back to later. Just click the Book- mark button at the bottom right or use the b key-board shortcut. You will see the Create Bookmark dialog box.

Enter a name for your bookmark and an optional note, then click Save or press Return. The book-mark will then be visible as a thin line in the time-line. You can access your bookmarks by clicking My Bookmarks at the top of the screen or via Video Bookmarks in the Sidebar. Just click the bookmark to go to your previously marked point. To delete a bookmark, click the Trashcan icon to the right of the bookmark and confirm your deletion by click-ing Yes.

Resizing Your Window

The player interface gives you a few different op-tions for resizing your window to fit your needs.

Click the Full-Screen icon 1 to enter Full-Screen mode. You can exit Full-Screen mode by clicking the icon again or by pressing the Esc key. You can also dynamically resize your window while watch-ing simply by grabbing the lower-right corner of the window and dragging until the window is the size you want.

In the application versions of the course, you can also choose Watch-and-Work mode 2 from the player. This takes you to a smaller screen that leaves room for you to work in another application alongside the course. Click the Standard button to return to a regular-size screen.

The Sidebar

The Sidebar is an area on the right side of the player where additional information, such as a description of the video you’re watching, is displayed. At the bottom are buttons that enable you to access your bookmarks or a list of videos in the chapter. To turn the Sidebar on or off, you can press Tab or click the button in the navigation bar.

1 2

xii introDuCtion

Test Yourself

This course includes a number of Test Yourself sec-tions, each of which contains a series of questions about the topics covered in that chapter.

Just click the box for the right answer. Some ques-tions refer to an image that is displayed on your screen.

Introduction

After answering any question, click the Submit Answer button at the bottom left to indicate that you’re finished. A dialog box will pop up to let you know whether you got the question right. (If you get a question wrong and want to see the correct answer, press and hold f, a, and N on your key-board at the same time. A check mark will appear in the box next to the right answer.) This dialog box also contains a button that will take you to the next question.

When you’re finished answering all the questions, click Training Content to return to the table of contents.

Aboutvideo2brainvideo2brain (video2brain.com) has been Europe’s premier source for video training since 2002. We produce high-quality English, German, French, and Spanish video training on a variety of software topics, with a special emphasis on graphics, web design, photography, and programming. Our customers include people just starting out, professionals, educational insti- tutions, and global corporations as well as home enthusiasts.

All of our courses are available in 1280 x 720 Hi-Def video, with a full-screen mode that creates an immersive learning experience. They also include an interactive, easy-to-use interface; custom bookmarks that let you annotate your course and remember where you left off; and “Watch-and-Work” mode, so you can practice as you learn.

We’re passionate about teaching and about help-ing you build exceptional skills so you can create extraordinary work. Our mission is to provide the best and most affordable video training possible, and to offer you a feature-rich learning environ-ment aimed at enhancing the effectiveness of our training.

video2brain was founded by Gerhard Koren, a v2b trainer himself. Our home office is nestled among the mountains of the Austrian Alps in the city of Graz, a “student city” with six universities.

AboutTimGreyTim Grey is regarded as one of the top educators in digital photography and imaging, offering clear guidance on com-plex subjects through his writing and speaking. He has written more

than a dozen books on digital imaging for photographers, including the best-selling Photoshop CS4 Workflow and Color Confidence. He has also had hundreds of articles published in magazines such as Digital Photo Pro and Outdoor Photographer, among others. He publishes the Ask Tim Grey email newsletter, as well as the Digital Darkroom Quarterly print newsletter. Tim teaches through workshops, seminars, and appearances at major events worldwide.

MasteringexposureinDigitalphotography:learnbyViDeo xiii

AbouttheAuthors

Exposure Math

2 exposureMath

Admittedly, most of this math happens behind the scenes, and there’s not a tremendous need to understand the particulars. For example, is there really a significant benefit to fully comprehending how pixel values are being adjusted as you increase the saturation of a photo? Certainly the more you understand what’s going on, the better equipped you’ll be to make the most of your digital photos, but there’s no question that some of the math you could understand wouldn’t provide much benefit other than the comfort of actually knowing.

There is one calculation, however, that affects the quality of every photograph you take: exposure.

TheValueofExposureMathConsidering that the moment of exposure truly defines the amount and quality of information contained within the photographic image, it stands to reason that exposure is critical. While today’s digital cameras do a remarkable job of calculating proper exposure under a wide variety of lighting conditions, the photographer must get directly involved in evaluating, and when necessary over-ruling, those calculations in order to produce the very best image.

UnderstandingExposureMath

In my experience most photographers aren’t exactly big fans of math. Quite often I’ve seen their eyes start to glaze over as soon as the subject is raised. And yet, photography in many respects is all about math. From calculations related to focal length and depth of field, to exposure, to adjustments applied using software tools after the capture, there is a tremendous amount of math going on.

MasteringexposureinDigitalphotography:learnbyViDeo 3

TheStopThe math related to calculating exposure revolves around the notion of the stop, which is often mis-understood. We talk about stops of light, and yet a stop isn’t exactly a unit of measure that defines a specific quantity of light. To be sure, a stop is used to measure light, but not in a direct sense.

It is most certainly possible to measure light in terms of quantity, which would largely be a matter of measuring the amount of energy being emitted by a particular light source. For example, the lumen is a measure of the quantity of light, and it has a fixed value.

A stop, however, doesn’t have a fixed value in terms of quantity of light; it is a relative value. When we say we’re adding a stop of light, what we’re actually saying is that we’re doubling the amount of light. Two stops would be four times as much light, because we’ve doubled the amount of light twice. Subtracting one stop means we’re cut-ting the amount of light in half.

So, there is obviously some math involved when it comes to stops, but that math is relative to a reference point. That reference point can generally be thought of as a proper exposure for the current lighting conditions, but the stop as a unit of measure is relative to a given reference value, not a measure of a specific quantity.

4 exposureMath

And of course, once all that work is completed, there is still much more work for the camera, including measuring sensor values for each pixel, applying noise reduction if applicable, calculat-ing the values that will be stored in the resulting file, writing that file to a digital media card, and a variety of other tasks.

At the most basic level, with a camera set to fully automatic mode, the photographer simply points the camera at a subject and presses the shutter release, letting the camera do the rest of the work. However, the photographer can always choose to get more involved, and to influence the final photo-graphic image in the process. Fundamental to this notion is the fact that a photographer doesn’t adjust exposure by simply turning a dial up or down to affect overall brightness, but rather by adjusting several individual controls. Those con-trols are the aperture, the shutter speed, and the ISO setting.

VariablesofExposure

A digital camera is incredibly busy when capturing an image. Consider all the work that has to be done for a typical exposure. The key subject in the frame must be identified and the distance to that subject must be determined. The exposure must be calculated based on the ambient light, the current metering mode, and other camera settings. The mirror must be moved up out of the way of the image sensor, the aperture must be closed down to the setting established with the current camera settings, and the shutter must be opened for the proper duration.


TheApertureA photographic exposure is created by projecting light onto an image sensor (or film, for those pho-tographers still inclined to capture on film). That light passes through an aperture, which you can think of as a gate or a hole; a series of blades allow you to adjust the size of that hole.

The size of the aperture is measured as a ratio relative to the lens’s focal length. The focal length of the lens is divided by the diameter of the cur-rent aperture opening, and the result provides the f-number that is used to describe the current aper-ture setting. This relationship is a common source of confusion among photographers, because as the aperture becomes smaller, the number used to describe it grows larger.

The reason for this apparent disparity is actually quite simple when you consider the math. For example, if we assume a focal length of 100mm and an aperture diameter of 4.5mm, the aperture value would be about f/22 (100/4.5 = 22.2). A larger aperture that measures 18mm in diameter would yield an aperture value of f/5.6 (100/18 = 5.55).

This relationship between lens focal length and aperture diameter is the reason the aperture value is generally written as a fraction, such as f/2.8 or f/8. Think of the “f” as lens focal length and the relationship becomes quite clear, as long as you’re able to think a bit in terms of the math involved.

6 exposureMath

When you adjust the aperture for the lens, you are adjusting the amount of light that will be projected for the final exposure. While the aperture numbers available to you might seem somewhat arbitrary, they are in fact based on the concept of the stop, which also helps explain why aperture settings are referred to as f/stops.

The f/number for a given aperture setting relates to the focal length of the lens and the actual diameter of the aperture opening. The different aperture settings available relate to a doubling or halving of the amount of light being projected. Let’s assume f/8 as our starting point. If we wanted to double the amount of light, we would need to open the aperture even further, specifically to an aperture of f/5.6. If, on the other hand, we wanted to cut the amount of light in half, we would need to close the aperture somewhat, to a setting of f/11.

The move from f/8 to f/5.6 is a change of one stop of light, because an aperture of f/5.6 will allow twice as much light to pass through the lens com-pared to f/8. The move from f/8 to f/11 will allow half as much light, and so that too is a change of one stop of light. When reducing the amount of light (moving to a larger f/number) we say that we are “stopping down” the lens. When increasing the amount of light we tend to say we are “opening up” the lens aperture.


ShutterSpeedAn image is captured by recording the light that passes through the aperture and strikes the image sensor. In order to control the amount of light actu-ally recorded, and thus ensure a proper exposure, the exposure must be timed. This is the job of the shutter mechanism, and the amount of time for which the shutter allows the light to strike the image sensor is the shutter speed. This is a simple measure of the duration of time expressed in sec-onds. For example, a fast shutter speed might be around 1/500th of a second, while a slow shutter speed might be several seconds.

There is a direct—though inverse—relationship between aperture and shutter speed. The larger the aperture opening, the less time the shutter must remain open to ensure a proper exposure. The smaller the aperture opening, the longer the shutter must remain open.

Measuring the shutter speed and understanding that measurement are of course simpler than the concepts behind the aperture. However, like the aperture setting, shutter speeds are measured based on stops of light. We adjust shutter speeds in increments that relate to doubling or halving the amount of light being recorded.

8 exposureMath

For example, let’s assume a base shutter speed of 1/60th of a second, with the assumption that at the current aperture setting this will yield a proper exposure. If we want to double the amount of light we need to leave the shutter open twice as long. So instead of 1/60th of a second, we could use 1/30th of a second. This is double the duration, and thus double the amount of light, and that means the result is one stop more light, or a one-stop brighter exposure.

By contrast, if we wanted to reduce the amount of light, we would need to leave the shutter open for a shorter duration. So to reduce the amount of light by half, or one stop, we would open the shut-ter for half as much time. In the case of a 1/60th-second exposure, that means using a shutter speed of 1/120th of a second. (Most cameras, for reasons of expediency related to other shutter speed val-ues, use 1/125th of a second for this value.)


TheISOSettingThe aperture and shutter speed need to be adjusted in concert with each other to produce a proper exposure. But what about situations where you can’t achieve a good combination based on your photographic needs? For example, if you want to stop the lens down to increase depth of field (the range of detail that is in focus in the frame), but the available light won’t let you use a fast enough shutter speed to render a sharp image while you are hand-holding the camera, what are you to do?

The answer is to adjust the ISO setting. A common misconception is that by increasing the ISO setting for your camera you are increasing the sensitivity of the image sensor. This actually isn’t the case. Based on its physical properties, an image sensor has a given sensitivity to light; you can’t change that. But you can apply amplification to the signal recorded by the image sensor, which produces a result that is similar to an increased sensitivity.

Because increasing the ISO setting actually applies amplification, however, there is also a side-effect that can be quite problematic at times: noise. When you amplify the signal, you aren’t somehow magically increasing the amount of information in the scene. In fact, by using a higher ISO setting you’re actually intentionally underexposing the image (capturing less light than you would for a proper exposure) and then applying amplification of the signal in order to brighten up the scene. You’re effectively trying to fill in information where information wasn’t captured. The result is random variations in tonal and color values for the pixels, which is what we refer to as noise in the image.

10 exposureMath

Of course, in certain cases you’ll need to make a compromise, risking noise in order to achieve an adequately fast shutter speed based on the aperture you feel is necessary to produce adequate depth of field. When you do adjust the ISO setting, you’re also making adjustments based on stops of light.

The base ISO setting for most digital cameras is 100. With film there were lower ISO values available (and some digital cameras do offer ISO settings below 100), but a 100 ISO value has be-come something of a baseline standard for digital exposure. This is the setting you would use when you want to capture an image based on the natural sensitivity to light of the image sensor.

If you want to apply amplification in order to achieve a faster shutter speed (creating the illu-sion of recording more light, effectively), you can increase the ISO setting to 200. Obviously the number 200 is double 100, and in this case that is no coincidence. A change from 100 ISO to 200 ISO applies amplification that is equivalent to one stop of light. In other words, increasing from a setting of 100 ISO to 200 ISO is producing a result that will look (with the exception of the additional noise) as though you had recorded twice as much light. Going from 200 to 400 ISO is another doubling of the exposure. And, of course, reducing ISO from 200 to 100 produces a result that looks as though you had captured half as much light.


When you adjust the ISO setting on your digi-tal camera, the idea is generally not so much to double (or halve) the amount of light, but rather to achieve a faster shutter speed. But that’s exactly when the notion of stops related to ISO settings becomes so valuable. If you increase the ISO by one stop (for example, from 100 ISO to 200 ISO) you can then increase the shutter speed by one stop (for example, from 1/30th of a second to 1/60th of a second). In situations where a faster shutter speed is critical (such as when you want to freeze motion or to capture handheld in a low-lighting situation), increasing the ISO is a relatively easy way to make the most of the current limitations.

Controlling Exposure

14 Controllingexposure

Both the aperture and the shutter speed can change the amount of light recorded for a given exposure. It is important that you have control over both factors, rather than a single exposure adjust-ment dial, because adjusting the aperture and shutter speed enable you to exercise considerable creative control over the photographic image.

By adjusting the size of the lens aperture, you are also adjusting the depth of field. A very large aper-ture (small f/number) will result in a very narrow depth of field, while a very small aperture (large f/number) will result in a very large depth of field. Of course, the potential depth of field depends on a variety of factors, including the distance to the subject and the focal length of the lens. The point is that varying the aperture will vary the depth of field. It is also important to keep in mind that any given lens has minimum and maximum aperture sizes, which in turn affect your flexibility in terms of both depth of field and exposure adjustment.

BlendingApertureandShutterSpeed

An understanding of the variables that relate to photographic exposure with a digital camera can be incredibly helpful, both in terms of your photographic knowledge and in terms of your ability to calculate the exposure settings that will produce the best result in a wide variety of situations.


By adjusting the shutter speed, you determine how moving subjects (or camera motion) will affect the final image. With a very fast shutter speed you can freeze motion, which can be useful for a wide variety of situations. That can mean both freezing the motion of a subject that is actually moving and also freezing the motion of the camera when you are hand-holding the camera rather than using a tripod or other support.

The key to adjusting exposure is to keep the aperture and shutter speed in balance with each other. As you increase the amount of light passing through the lens by opening up the aperture, you’ll need to reduce the length of time the shutter re-mains open. Conversely, if you want to stop down the lens in order to reduce the amount of light passing through the aperture, you’ll need to use a longer shutter speed in order to allow an adequate amount of light to reach the image sensor.

Both aperture and shutter speed settings use increments based on stops of light, which makes it relatively easy to determine how to adjust one or the other to ensure a proper exposure. For example, let’s postulate a situation where a proper exposure will be achieved at an aperture of f/8 and a shutter speed of 1/250th of a second. If you decide you want to open the aperture up a bit more in order to reduce the depth of field, you might choose a setting of f/5.6, which allows one stop more light (double the amount of light) com-pared to f/8.


That means you also need to adjust the shutter speed, in this case reducing the exposure time by half to 1/500th of a second. The aperture is allow-ing twice as much light to come through, but the shutter speed is letting half as much light reach the image sensor. So if you increase the amount of light by one stop using the aperture and reduce the amount of light by one stop using the shutter speed, the two remain in balance and you still have a proper exposure.

In this way, you could cycle through a series of aperture and shutter speed combinations, all of which would achieve the same exposure, but with different depths of field. If the largest aperture opening for a given lens is f/2.8, and we can achieve a proper exposure for the current lighting conditions by opening the shutter for 1/500th of a second, that means we could also achieve a proper exposure by using f/4 and 1/250th of a second, or f/5.6 and 1/125th of a second, or f/8 and 1/60th of a second, or f/11 and 1/30th of a second, or f/16 and 1/15th of a second. From the standpoint of photo-graphic exposure, all of these combinations will produce the same result.

Of course, from a more complete photographic perspective there may be some very significant dif-ferences among these exposures. For a typical lens the difference in depth of field between f/2.8 and f/16 is rather significant. At f/2.8 a very small range of the scene will be in focus. At f/16 most of the scene may be rendered in sharp focus. As a photog-rapher you can make an aesthetic decision based on the subject matter and your own preferences.


The shutter speed may play less of a role in the final result, depending on the subject. If you are photographing a landscape without any moving subjects, and the camera is firmly mounted on a tripod, you may not see any difference related to the shutter speed at all. However, if you are photo-graphing handheld or there are moving subjects in the scene, the shutter speed can play an impor-tant role.

As a general rule, when shooting handheld you should aim to use a shutter speed with a reciprocal that matches the lens focal length. For example, if you are using a 100mm lens, you should use a shut-ter speed of at least 1/100th of a second, so with most cameras you would opt for a shutter speed of 1/125th of a second or faster. With a 500mm lens, if you were shooting handheld (which calls for strong arms in addition to a steady hand), you would want to use a shutter speed of 1/500th of a second or faster. The reason a longer focal length lens requires a faster shutter speed, by the way, is that the smaller field of view of a longer lens will effectively magnify any motion. A faster shutter speed is necessary to compensate for that magni-fied motion.

When shooting with the camera mounted on a tripod, the question of shutter speed relative to focal length is no longer relevant. However, shut-ter speed can still be very much an issue when a subject in the frame is moving, and here again you are able to exercise creative control.


A typical example would be a photograph that includes moving water. Based on the ambient lighting conditions and the range of apertures supported by the lens you’re using, you’ll have a range of shutter speeds to choose from. A fast shutter speed would be able to freeze the water in motion, showing a very brief moment in time. A slow shutter speed would result in an image where the water is a silky blur in the frame. Both can be very impactful images, and it is up to you to decide which approach is more appropriate based on the scene and your intent.

Of course, you need to take into consideration the balance between the effects of shutter speed and aperture size. If you’re trying to achieve a deep depth of field in conjunction with a fast shutter speed, you may have a challenge on your hands. For example, let’s consider a situation where a proper exposure would be achieved at an aperture of f/8 and a shutter speed of 1/125th of a second. To achieve the desired depth of field, let’s assume you need to stop down by two stops to f/16. However, that also means you need to use a slower shutter speed—slower by two stops—in order to balance the exposure. That would require a shutter speed of 1/30th of a second in this example. But if you are including a relatively fast-moving stream in the scene, you might need a much faster shutter speed in order to freeze the motion. For example, you might need a shutter speed of 1/500th of a second in this case.


To achieve a 1/500th of a second shutter speed while maintaining the f/16 aperture, you’ll need to increase the ISO setting. In this example, going from a shutter speed of 1/30th of a second to 1/500th of a second means you need to adjust the shutter speed by a total of four stops. In effect, that means the exposure would be underexposed by four stops, using an aperture of f/16 and a shutter speed of 1/500th of a second, when that aperture under the current lighting conditions would normally call for a 1/30th of a second shut-ter speed.

It is therefore possible to balance the exposure using an aperture of f/16 and a shutter speed of 1/500th of a second by increasing the ISO setting by four stops. That means going from an ISO set-ting of 100 to an ISO setting of 1600 (from ISO 100 to 200 is one stop, from 200 to 400 is one stop, from 400 to 800 is one stop, and from 800 to 1600 is one stop). As a result, you would have reduced the available light by four stops by changing the shutter speed, but then compensated by applying amplification equivalent to four stops by increasing the ISO value.

In any given photographic situation, you are prob-ably focused primarily on either depth of field or shutter speed as your priority. In other words, you’re either thinking primarily about a deep or narrow depth of field or thinking about managing shutter speed to deal with a moving subject (or handheld camera). However, sometimes both of those factors will be high on your priority list, and you may need to employ a different ISO setting to achieve your goals.


HalfStopvs.One-ThirdStopThus far the discussion of stops has been limited to full stops, either doubling or halving the amount of light using the aperture, shutter speed, and ISO settings. However, most cameras allow you to exert a higher degree of control than is possible with one-stop increments.

In general, most digital cameras allow you to adjust exposure in half-stop increments. For example, changing the aperture from f/5.6 to f/8 means stopping down one stop, which will cut the amount of light in half. However, by working in half-stop increments you can also adjust the aper-ture to f/6.7. Assuming a scene would be properly exposed with an aperture of f/5.6 and a shutter speed of 1/125th of a second, you could stop down by one-half stop to f/6.7, and then increase the shutter duration by one-half stop to 1/180th of a second. Another half-stop would take you to f/8, with a shutter speed of 1/250th of a second.

Most digital cameras will also enable you to adjust exposure in one-third-stop increments. This provides a higher degree of precision in terms of exposure control, which can be helpful in certain situations. When adjusting the exposure settings using one-third-stop increments, instead of mov-ing two steps for each stop (for example, from f/5.6 to f/6.7 and then to f/8), you would take three steps (for example, from f/5.6 to f/5.3 to f/7.1 and then to f/8).


For most photographers, adjusting exposure in half-stop increments provides more than enough control. Working in half-stop increments also pro-vides the advantage of working with aperture set-tings that are more familiar. Most photographers who have been working with a digital SLR for any period of time (or who have ever taken a photog-raphy class or read an instructional photography book) are probably familiar with the common aper-ture settings such as f/5.6, f/6.7, f/8, f/9.5, f/11, and so on. When working with one-third-stop incre-ments the numbers between the primary aperture settings are different, which can sometimes prove confusing.


In general, you would apply exposure compensa-tion when you feel (or know) the camera’s light meter isn’t providing you with the most accurate information for the scene. For example, when you photograph a scene that is dominated by a bright subject, the camera’s meter assumes that the over-all scene needs to be darkened down. In effect, the camera is trying to make bright white areas appear as middle gray. In that case you would want to ap-ply exposure compensation to brighten the scene beyond what the camera thinks is appropriate. For example, when photographing a snow-filled scene, you will likely need to increase the amount of light captured by the camera by about one stop to compensate for how the camera’s meter thinks the scene should be rendered.

When working in one of the automatic exposure modes, such as aperture priority (Av, for Aperture value) or shutter priority (Tv, for Time value), ex-posure compensation is a way of taking advantage of the camera’s ability to calculate exposure and adjust the shutter speed or aperture automatically while leaving the value you’ve set for the aper-ture (in Av mode) or shutter speed (in Tv mode) unchanged.

ExposureCompensation

Another tool available to the photographer when calculating and adjusting exposure is exposure compensation. Here again, the unit of measure is the stop. You can compensate exposure up or down (brighter or darker) using stops of light, and depending on how you’ve configured your camera, by half-stop or one-third-stop increments as well.


When working in manual mode, exposure compen-sation is applied by simply adjusting the exposure as desired, using the camera’s exposure meter as a reference, and using settings that shift the ex-posure dark or light relative to what the exposure meter is showing you.

In either case, exposure compensation allows you to deal with situations where the camera might not understand exactly what you’re trying to accomplish as a photographer.

ConclusionThere’s a lot of math being done inside your camera before, during, and after the process of capturing a photographic exposure. While much of that math might be better left a mystery in order to avoid overloading your brain, there’s no question that having an understanding of how exposure is measured and calculated can help you work more quickly and intelligently as a photographer.

Some of the math might involve mental gymnas-tics, but in general the basic concepts are relatively straightforward. If you pay attention to your cam-era settings and how they are being adjusted while capturing a variety of images, the concepts related to exposure calculation will become easier to understand, and you’ll get much better at achiev-ing the perfect exposure in your photographs.

Glossary

addiTive color MixiNG The process of mixing red, green, and blue light emitted from a source to produce a wide range of colors. See also “subtractive color.”

aNTi-aliaSiNG A pixel-processing technology that eliminates or softens the jaggedness of low- resolution curved edges.

aPerTure An adjustable diaphragm opening inside a photographic lens that regulates the amount of light passing through it during the exposure process. The size of an aperture is usually calibrated in f-stops, such as f/1.4 or f/2.8.

aPerTure PrioriTy The setting on a DSLR camera that allows the photographer to choose a specific aperture value while the DSLR selects a matching shutter speed to ensure the correct exposure.

arTifacTS Color or line errors that visibly impact the image in a negative way. Artifacts are often the result of excessive image compression.

auTo exPoSure An in-camera exposure system that is able to calculate and adjust the shutter speed and aperture (and CCD sensitivity in many digital cameras) to achieve the best exposure for the subject under present conditions, such as the lighting situation.

auTofocuS The feature of a camera or lens that enables it to focus itself electronically to the appropri-ate subject distance.

biT (biNary diGiT) The smallest unit of information in a computer. Bits can have only two values: 0 or 1.

biTMaP A digital image file that uses spatially arranged pixels to store the image information. Some-times, the term bitmap implies a color depth of one bit per pixel only, resulting in a two-color image.

blacK PoiNT The darkest point in a color space. Black points in RGB color spaces usually describe a perfect black (lightness 0). In print, the darkest possible color value will never be completely black. Hence, black points in printer color spaces are always brighter than a perfect black.

blurriNG The process of adding fuzziness to or decreasing the focus of an image or a certain image region for a softer appearance or to camouflage a defect.

boKeH Describes how a photographic lens renders blurred/out-of-focus image areas. Typically the out-of-focus portions of the picture distinguish the look and feel of different lens types.

bridGe caMera A medium-size digital camera with an electronic viewfinder and long zoom lens that fills the niche between the compact camera and the single-lens reflex camera (SLR).

caMera SHaKe The blurring or ghosting of an image due to camera movement, usually unintentional.

cHaNNel A component of a digital image that car-ries information for one color parameter of the color mode used (RGB, CMYK, HSB, LAB). The combination of all channels yields a full-color composite image.

cMS (color-MaNaGeMeNT SySTeM) A program that helps to match the color of input and output devices throughout the workflow in order to produce predict-able results.

cMyK Cyan, magenta, yellow, black: the process colors used in four-color printing. See also “subtrac-tive color.”

color coNverSioN The act of changing the color mode of an image.

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26 glossary

Glossary

color correcTioN The process of modifying the pixels in a digital image in an effort to improve the appearance of the image or to correct obvious defects.

color dePTH A measure of how many colors can be in a pixel of an image. Also called bit depth. 1-bit equals two colors (21), 8-bit color equals 256 colors (28), and so forth. One pixel of an RGB image, which is represented by three 8-bit color channels, has over 16 million possible color values (28 red channel x 28 green channel x 28 blue channel). RGB images using 8 bits per color channel are sometimes referred to as 24-bit images (8 bits per channel x 3 channels).

color GaMuT The range of colors that can be repro-duced by all possible combinations of a given system’s colorants, such as the colors that can be reproduced using process colors in commercial printing.

color Model A mathematical model for the descrip-tion of color, such as RGB, LAB, or CMYK.

color SPaceS In a color space, each visible color is assigned a distinct position in terms of coordinates. The total of all possible colors inside a given color system (like RGB or CMYK) adds up to a virtual shape inside this coordinate system. This shape is called a color space. Reproduction media like computer screens cannot display all visible colors. Printing or photographic reproduction technologies also have various intrinsic limitations of color reproduction. If colors are to be reproduced, meaning to be trans-ported from one medium to another, you need to know the color limitations of the different media. This is exactly what color spaces and gamuts are about—they are mathematical descriptions of the total number of displayable colors. Color spaces are vital components of the information being saved in color profiles.

coMPreSSioN File-size reduction by various math-ematical algorithms. Depending on the technology, compression can be lossless or lossy, with the latter resulting in a loss of image quality and/or resolution.

coNTiNuouS ToNe An image with continuous shades of color or gray tones, such as a photograph.

coNTraST The relationship and degree of difference in color and light between parts of an image.

dePTH of field The portion of a scene that appears sharp in a photograph. Only one distance can be precisely in focus, and the decrease in sharpness is gradual. The depth of field also describes the range of distances still perceived as being sharp.

diGiTal zooM A method of zooming via resampling (interpolation) of the available image data. The image quality is thereby reduced.

dPi (doTS Per iNcH) A measurement unit for the resolution of page printers, phototypesetting machines, and graphics screens.

dSlr Digital single-lens reflex camera.

dyNaMic raNGe The range between the lightest and darkest areas of an image. Also used to describe the limits of luminance range that a digital camera, a scanner, or film can capture.

exPoSure The total amount of light a photographer allows to fall on the film or the sensor during the process of taking an image.

exPoSure coMPeNSaTioN A technique used to increase or decrease the exposure to compensate for dark or light subjects that cause a light meter to indicate a less-than-optimal exposure.

filTer A routine containing algorithms to modify digital images by changing the values or arrangement of specified image areas.


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focal leNGTH The distance from the optical center of a lens to the focal point that is located on the sen-sor or film if the subject is in focus. The focal length also determines the field of view of a given lens.

f-SToP The ratio of the focal length to the aperture of a lens; used to measure of how much light is enter-ing a camera lens.

GaMMa In digital imaging, gamma refers to the encoding of linear brightness values captured by a device (e.g. a camera) to match the contrast and brightness of human perception.

GaMuT See “color gamut.”

GraiN This term originates in analog photography where, especially in light-sensitive film material, the silver or pigment particles introduce graininess. In digital photography, a comparable effect occurs when high ISO ratings make the image appear out of focus in some areas.

GrayScale An image composed exclusively of shades of gray, varying from black at the weakest intensity to white at the strongest, usually using 256 different tones.

HiGHliGHTS The brightest areas in an image.

HiSToGraM A bar graph representation of the tonal values (brightness or color) in an image based on the frequency of occurrence of each value.

iSo ( iNTerNaTioNal orGaNizaTioN for STaNdard-

izaTioN) An international organization that sets standards. In digital photography, the ISO exposure index is the equivalent of film speed in analog pho-tography. It is the measure of the camera’s exposure in response to a light level measurement. The lower the ISO number, the less sensitive the camera is to light. In darker situations higher ISO settings are used to get faster shutter speeds.

JPeG A lossy compression algorithm that reduces the file size of digital images. Image quality is reduced in proportion to the amount of compression. Typically, about 10:1 compression is possible with little percep-tible loss in image quality.

layer A feature of graphics software in which ele-ments are isolated from each other so they can be hidden, reordered, or otherwise manipulated without affecting other elements in the composition.

leNS SPeed Refers to the maximum aperture diam-eter available on a photographic lens. A lens with an aperture of f/5.6 is slow; a lens with an aperture of f/2 or under is fast.

MaSKiNG A technique used to hide certain areas of an image or design or to exempt them from manipulations.

MeTadaTa Data that stores information about the characteristics of media files, such as image size, the ISO rating or f-stop at which an image was taken, user-defined tags, and so on.

MidToNeS The tonal range between highlights and shadows.

NeuTral Any color absent of hue or having the same value in all three RGB channels, such as white, gray, or black.

NeuTral deNSiTy filTer A gray or colorless filter that reduces and/or modifies the intensity of the wavelengths or colors of light that passes through it without changing the hue.

NoiSe A random pattern of brightness or color information that appears in an image. Noise is often caused by long exposures or high ISO settings.

NoiSe reducTioN A filter treatment used to sup-press image noise in shots taken at high ISO levels.

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Glossary


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Basic digital cameras simply apply a higher JPEG com-pression ratio to achieve this, while high-end cameras use specialized sensors and algorithms.

ouT-of-GaMuT color A color that cannot be repro-duced by a specific color model. For example, some RGB colors fall outside the CMYK gamut.

Pixel Picture element: the smallest unit of informa-tion in a digital image. Pixels are usually arranged in a two-dimensional grid. Depending on the output device, they are often represented using squares or dots.

PolariziNG filTer A filter designed to increase color saturation and decrease reflections on surfaces such as water and glass. Polarizing filters are often used in landscape photography, where the sky can appear washed out, to deepen shades of blue and increase the contrast between clouds and sky.

raW Collective term for image file formats—mostly camera manufacturers’ proprietary formats—used for unmodified and lossless storage of all sensor data. Adobe introduced the DNG (digital negative) file format in an attempt to unify these RAW file formats. You can edit RAW files in the Adobe Camera Raw application.

reSaMPliNG Recalculating the pixels of an image to change the physical size of the file.

reSoluTioN The detail level of an image described as density of graphic information in dots per inch (dpi) or pixels per inch (ppi).

reToucHiNG The process of making selective manual or electronic corrections to images.

rGb Additive color model using red, green, and blue as primary colors to describe the RGB color space, which is a subset of the visual color spectrum. RGB

values are numeric triples (red, green, blue) repre-senting how much of each primary color is used to describe a specific color in the RGB color space. Please note: RGB values do not describe colors independent of device without color management.

SaTuraTioN The intensity or purity of a specific color; a completely desaturated color is gray.

ScaliNG Changing the size of an image. If an image is scaled proportionally, the aspect ratio remains unchanged.

SeNSor The built-in sensor of a digital camera replaces traditional film media as a light-sensitive element. A sensor is an electronic image converter. In high-quality digital cameras, both CMOS (comple-mentary metal oxide sensor) and CCD (charge- coupled device) sensors are used.

SHarPNeSS The subjective density difference between two tones at their boundary, interpreted as fineness of detail.

SHuTTer The electronic mechanism inside the cam-era that opens and closes to create the exposure. It limits the time for which the image sensor is exposed to light.

SHuTTer laG The delay between the moment the shutter is triggered and the moment the image is actually recorded.

SHuTTer SPeed The length of time for which a cam-era’s shutter remains open when the shutter release button is triggered.

SToP doWN To reduce the lens aperture, thus increasing the f-stop number in order to increase the depth of field of the image or to take the photo after focusing it with the aperture fully open.

30 glossary

SubTracTive color Subtractive color systems start with white light and subtract certain wavelengths to produce colors. See also “CMYK,” “additive color mixing.”

THuMbNailS Scaled-down preview versions of images, layers, or pages. These allow you to preview the files without actually opening them.

TraNSPareNcy The quality of an image element with an opacity value below 100 percent that allows background elements to partially or entirely show through.

uNSHarP MaSKiNG A digital image manipulation technique that increases the acutance, or apparent sharpness, of photographic images. It locates the edge between sections of differing lightness and exaggerates the difference across the edge, thereby increasing edge contrast.

Glossary

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Booklet Mastering Exposure in Digital Photography Lbv

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