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Basic Photo Tips: Aperture, Shutter Speed, and ISO

by Bryan F Peterson, August 2008

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: “Wow, 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: “Hey Bryan, 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, every photographer 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). Whew! 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.


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.


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 200 than 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 ISO back 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 to ISO 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 from Bryan will explain in detail how to correctly expose your photographs.


About the Author

Bryan F Peterson has been a full-time commercial photographer since 1981, shooting assignments all over the world for many of the Fortune 500 companies, including Kodak, UPS, and American Express. He is also a contract stock photographer for Corbis and Getty. He has been a contributing editor at Outdoor Photographer Magazine and is currently a contributing editor at Popular Photography and Imaging Magazine. Within the photographic community, he is most noted as the author/photographer of four best selling “how-to” photography books: Understanding Exposure, Understanding Shutter Speed, Learning to See Creatively and Beyond Portraits, with two new books due out in the spring of 2009: Understanding Close-up Photography and The Field Guide to Photography. He is also the founder and one of the instructors at Picture Perfect School of Photography, an on-line photography school. More »

Example Images from Bryan’s Gallery

Text ©2008 Bryan F Peterson. Photos ©2008 Bryan F Peterson.

Article created August 2008

Readers' Comments

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Master Faster , August 20, 2008; 05:08 P.M.

A very good and simple explanation on the basics. I'm a beginner, in DSLR age, but used to shoot RFs in manual mode before. About the article, my wish list would include types of metering , that would help really more...MF

Michael Evans , August 20, 2008; 11:55 P.M.

Good information. Thanks for taking the time to make some things easily understandable. I like to reread articles to to refresh knowledge.

Tim Summa , August 21, 2008; 10:09 P.M.

Bryan, excellent presentation on the basics of photography; you are doing a vary fine job of presenting solid information, keep this up. It is a delight that a person can understand these things, organize them into a neat package and then deliver them clearly and concisely. The humor of the worker bees approach was nice, it reminded me of a pre WWII article from Eastman Kodak using little men as working to ‘expose’ by building an image of the scene on a piece of film. Good humor in education helps to both illustrate and act as a memory minder. Tim Summa MFA

Victor Wei , August 22, 2008; 12:38 P.M.

Great tips - I find the advice on how to shoot with manual settings particularly helpful for beginners who may feel shooting manually intimidating. Thank you, photo.net, for bringing Bryan in for us.

Ronda Sliter , August 23, 2008; 02:13 P.M.

I am a beginner, and these tips are easy to understand. I will refer to this article a lot until its committed to memory. Thank you!

Paul Trunfio , August 24, 2008; 04:29 A.M.

Great for a beginner. But Bryan left out a lot of details for trickier exposures (like dark or light backgrounds, shooting the sky with the sun in the frame, motion, isolation, etc) that I hope he will get to someday. If you cannot wait, all this and more can be found in his "Understanding Exposure" book. The first edition was published in 1990 and, as a beginner then, it was an indispensable learning tool for me and my fully manual film camera. Lots of techniques, without all the fluff (i.e., concise). A beginner cannot learn from anyone better. Welcome to photo.net.

Rick Ogan , August 24, 2008; 11:41 A.M.

This is great stuff as I am new to Digital SLR's and has been many years since someone needed all of my film camera's and lense's more than I did. Keep this up I love it. Thanks

Nick Mc , August 31, 2008; 02:09 P.M.

Great article. I only skimmed it so I may have missed this detail, but I did not see an explanation of the consequences of high ISOs. This is very important for beginners to know, otherwise many may think that the higher the ISO the better the picture in any situation.

R. A. Haentzler , September 16, 2008; 04:55 P.M.

I have read 3 of Bryan's books and have found them not only informative but very well written. His passion comes through with each paragraph. In my opinion he has a way of simplifying the art of taking pictures or should I say taking creatively correct exposures. I am looking forward to his two future books that are coming out. -Bob Haentzler, Waterloo IL

omid semiari , September 29, 2008; 02:37 P.M.

Thank you Bryan for your comprehensible article. since I'm a new comer on DSLR, it was really helpful. I'd wait for your piece of advices for the first steps on photography that should be taken. thank u again . omid

Thomas Alanoly , December 03, 2008; 05:21 A.M.

Bryan did it as simple as breast-feeding a newborn, speaking their language ! Wholesome and easily digestible.

Roberto Anil , December 19, 2008; 09:21 A.M.

Fantastic explanation in a very simple way. Thanks

Paul Kerr , February 02, 2009; 12:17 P.M.

The clearest description I have had the pleasure to read on these essentials. VERY helpful to a newbie such as myself.

Monique B , April 05, 2009; 07:30 P.M.

LOL....finally I understand my camera....woo hoo! Think I just had one of those light bulb moments! Thanks so much for this article.

Gabriel Hughes , September 27, 2009; 03:41 P.M.

At LAST, even I could grasp this tutorial, now I can let my creative side go wild:) Thanks

Sharon Johnson , December 17, 2009; 04:09 P.M.

Good article. A lot of discussions I've seen on this site ( and others ) only talk about aperture and shutter speed when trying to diagnose someone's exposure problems. It seems like they've never heard of ISO. I used to search far and wide for Kodachrome 25. Kodachrome 64 was acceptable, but 100 was only if you were desperate. Now with a DSLR I've had to raise my acceptability limits quite a bit, but ISO problems can still surface ( think "noise" has been substituted for "graininess" ).

David Thewlis , December 30, 2009; 03:23 A.M.

Great explanation! I also found playing around with the values on this page really helped me a lot: http://www.photonhead.com/beginners/stops.php

Amber Marie , January 19, 2010; 07:17 P.M.

This was very interesting and helpful. It refreshed my memory of all the things i learned in photo one a year and a half ago. Since then, I have gotten more and more into photography. Thanks for the refresher!

Nick Gonzales , April 14, 2010; 01:55 P.M.

This was excellent. You put it into such easy terms a kid could understand this.. Just one suggestion.. Cut your hair dude..

J John , May 12, 2010; 01:08 P.M.

This couldnt have been explained in a better way. I wish I could retain everything in my head as I shoot pictures. Will keep coming back to this page to refer. Thanks for the great work you professionals are doing to educate the rest.

Amy Thompson , September 20, 2010; 07:40 P.M.

I did this practice with my Canon EOS Rebel T1i, and I believe I understand emotional (for a lack of a better word) how to relate the aperature with the shutter speed, I love the difference when I adjusted the shutter speed for black and white in the manual mode, but I am having difficulty understanding why i would need to bump up the ISO.  Does it clarify the objects in the photo more?  Does the ISO give more definition while the aperature and the shutter speed allow the light to soften it otherwise?  I think I am a bit confused....sorry only had my camera for about a year...still learning.

Charles Owen Hoffman Smith , October 02, 2010; 01:11 A.M.

    Bryan I have attended two photo courses run by the same guy here in my home town and in neither case did he explain the basics as well as your article. I look forward to reading more. Thank you it has helped a great deal, Charlesowen


John Ramos , March 20, 2011; 07:54 A.M.

huh! very well said Bryan...well explained guide...at last i found a guide to help me understand my new toy...many thanks Bryan...It pushes me to sign in and register here in photo.net , only just to add a comment from your wonderful article...great job!

I'm looking forward, for more of your article...many thanks...

Kathy Jones , July 12, 2011; 02:23 P.M.

I really enjoyed this article...it really help me to further understand apertures and shutter speeds a lot.  I do have one question...you mention to look in your view finder when your in Manual mode to help you find the correct shutter speed until the camera's light meter indicates correct, do all cameras/lenses have this feature?  Sorry if I sound stupid, but I didn't see anything letting me know.  Just thought I'd ask.  I have a Nikon D60.

Your photography is wonderful and very inspirational.  Thanks for sharing.

Ramakrishnarao Rebbapragada , March 04, 2012; 03:12 P.M.

This is a great article. I am a late entrant in to photography, but I would like to go into it in a systematic manner and progress slowly and steadily. 

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