Exposure basics

Gary Hart Photography: Glisten, Diamond Beach, Iceland

Glisten, Diamond Beach, Iceland
Sony a7R III
Sony 12-24 f/4 G
1/25 second
F/18
ISO 100

With advanced exposure and metering capabilities, cameras seem to be getting “smarter” every year. So smart, in fact, that for most scenes, getting the exposure right is a simple matter of pointing your camera and clicking the shutter button. That’s fine if all you care about is recording a memory, but not only is there more to your exposure decision than getting the amount of light in your picture, there are many reasons to over- or underexpose a pictures. For the creative control that elevates your images above the millions of clicks being cranked out every day, giving control of one of its most important responsibilities to your camera overlooks an undeniable truth…

Your camera is stupid

Sorry—so is mine. And while I can easily cite many examples, right now it’s just important that you understand that your camera thinks the entire world is a middle tone. Regardless of what its meter sees, without intervention your camera will do everything in its power to make your picture a middle tone. Sunlit snowman? Lump of coal at the bottom of your Christmas stocking? It doesn’t matter—if you let your camera decide the exposure, it will turn out gray.

Modern technology offers faux-intelligence to help overcome this limitation. Usually called something like “matrix” or “evaluative” metering, this solution compares a scene to a large but finite internal database of choices, returning a metering decision based on the closest match. It works pretty well for conventional, “tourist” snaps, but often struggles in the warm or dramatic light artistic photographers prefer, and knows nothing of creativity. If you want to capture more than documentary “I was here” pictures, you’re much better off taking full control of your camera’s metering and exposure. Fortunately, this isn’t nearly as difficult as most people fear.

Laying the foundation

The amount of light captured for any given scene varies with the camera’s shutter speed, f-stop, and ISO settings. Photographers measure captured light in “stops,” much as a a cook uses a cup (of sugar or flour or almonds or whatever) to measure ingredients in a recipe. Adding or subtracting “stops” of light by increasing or decreasing the shutter speed, f-stop, or ISO makes a scene brighter or darker.

The beauty of metering is that a stop of light is a stop of light is a stop of light, whether you control it with the:

  • Aperture: The opening light passes through when the shutter opens, measured in f-stops
  • Shutter speed: The time the shutter is open, allowing light to pass through the aperture to reach the sensor—slower shutter speeds mean more light; faster shutter speeds mean less light
  • ISO: The sensitivity of the sensor (or film) to light

But while an aperture stop adds/subtracts the same amount of light as a shutter speed or ISO stop, the resulting picture can vary significantly based on which exposure variable combination you choose. Your shutter speed choice determines whether motion in the frame is blurred or frozen, while the aperture choice determines the picture’s depth of field. And while an ISO stop also adds/subtracts the same amount of light as shutter speed and aperture without affecting motion and depth, image quality decreases as the ISO increases. So getting the light right is only part of the exposure objective—you also need to consider how you want to handle any motion in the scene, and how much depth of field to capture.

For example, let’s say you’re photographing autumn leaves in a light breeze. You got the exposure right, but the leaves are blurred. To freeze that blur, you halve the time the shutter is open (faster shutter speed) to freeze the motion, but also reducing the light reaching the sensor by one stop. To replace that lost light, you could open your aperture by a stop (change the f-stop), double the ISO, or make a combination of fractional f-stop and ISO adjustments that total one stop. That’s a creative choice your camera isn’t capable of.

Metering modes

Today’s cameras have the ability to measure, or “meter” the light in a scene before the shutter clicks. In fact, most cameras have many different ways of evaluating a scene’s light. Your camera’s metering mode determines the amount of the frame the meter “sees.” The larger the area your meter measures, the greater the potential for a wide range of tones. Since most scenes have a range of tones from dark shadows to bright highlights, the meter will take an average of the tones it finds in its metering zone.

Metering mode options range from “spot” metering a very small part of the scene, to “matrix” (also know as “evaluative”), which looks at the entire scene and actually tries to guess at what it sees. Each camera manufacturer offers a variety of modes and there’s no consensus on name and function (different function for the same name, same function for different names) among manufacturers, so it’s best to read your camera’s manual to familiarize yourself with its metering modes.

Since I want as much control as possible, I prefer spot metering because it’s the most precise, covering the smallest area of the frame possible, an imaginary circle in the center three (or so) percent (depending on the camera) of what’s visible in the viewfinder. Spot metering, I can target the part of the frame I deem most important and base my exposure decision on the reading there.

Spot metering isn’t available in all cameras. In some cameras, the most precise (smallest metering area) metering mode available is “partial,” which covers a little more of the scene, somewhere around ten percent.

Exposure modes

Don’t confuse the metering mode with the exposure mode. While the metering mode determines what the meter sees, the exposure mode determines the way the camera handles that information. Most DSLR (digital single lens reflex) and mirrorless cameras offer manual, aperture priority, shutter priority, and a variety of program or automatic exposure modes. Serious landscape photographers usually forego the full automatic/program modes in favor of manual (my preference) or aperture/shutter priority modes that offer more control.

If you select aperture or shutter priority mode, you specify the aperture (f-stop) or shutter speed, and the camera sets the shutter speed or aperture that delivers a middle tone based on what the meter sees. But you’re not done. Unless you really do want the middle tone result the camera desires (possible but far from certain), you then need to adjust the exposure compensation (usually a button with a +/- symbol) to specify the amount you want your subject to be above or below a middle tone.

For example, if you point your spot meter at a bright, sunlit cloud, the camera will only give your picture enough light make the cloud a middle tone—but if you’ve only given your scene enough light to make a white cloud gray, it stands to reason that the rest of your picture will be too dark. To avoid this, you would adjust exposure compensation to instruct your camera to make the cloud brighter than a middle tone by adding two stops of light (or however much light you want to give the cloud to make it whatever tone you think it should be).

Rather than aperture priority, I prefer manual mode because I never want my camera making decisions for me. And once it’s mastered (a simple task), I think manual metering is easier. In manual mode, after setting my aperture (based on the depth of field I want), I point my spot-meter zone (the center 3% of the scene in my viewfinder) at the area I want to meter on and dial in whatever shutter speed gives me the amount of light I think will make that subject (where my meter points) the tone I want. That’s it. (In manual mode you can ignore the exposure compensation button.)

Trust your histogram

I see many people people base exposure decisions on the brightness of the image on the LCD. The typical approach is some variation of: 1) Guess at the exposure settings 2) Click 3) Look at the picture on the LCD 4) Adjust 5) Repeat. Not only is this approach lazy, it’s a waste of time and woefully inaccurate.

I call it lazy because these photographers (but of course I don’t mean you) don’t care enough about their craft to apply a skill that only takes minutes to learn (see above), a skill that will serve them best in the most difficult exposure situations. But that’s not the real problem—the real problem is the inaccuracy introduced by trusting the image on your LCD.

LCDs vary in brightness because viewing conditions change. With a brightness adjustment in every camera’s menu, many photographers simply turn their brightness to maximum because it’s easier to see, especially in sunlight, and a bright picture usually looks better. Other photographers use an auto-brightness setting that adjusts with ambient light—the more light it detects, the brighter the display.

Regardless of your LCD’s brightness setting, the variation in brightness of the screen and/or the ambient light make the image on the LCD a very unreliable exposure indicator. When people tell me their images are usually too dark on their computer or in prints, the first thing I do is check the brightness of their camera’s LCD—if it’s set to maximum, they’re likely fooled into thinking the exposure was brighter than it actually was.

How do you fix this? Simple: Learn to read a histogram, and never use your camera’s LCD for exposure decisions again. The histogram is as simple as it is useful.

Day's End, Ke'e Beach, Hawaii

Day’s End, Ke’e Beach, Hawaii

Ke'e Beach histogram

A histogram is a plot of the tones in an image. I’ll save a more complex explanation for another day, but all you really need to know is that the graph starts with black on the left and brightens to white on the right. Every pixel in the image is sampled for its brightness—the brighter it is, the farther to the right it falls on the histogram. Anything in the image that’s too dark to display detail (black) is “clipped” (cut off) on the left side; anything in the image that’s too bright too display detail is clipped on the right. Ideally, nothing will be clipped on either side. If your scene contains a greater range of light (dynamic range) than will fit in the histogram, one side or the other will clip and you have exposure decisions too make—HDR (blending multiple exposures), graduated neutral density filters, or deciding that it’s okay to lose one side or the other (shadows or highlights). For example, the Ke’e Beach image above is predominantly middle tones, with just a few extremely bright and extremely dark pixels.

One more time

So let’s review. Start by selecting your metering mode (the way your meters”sees” the scene: spot, partial, matrix, and so on), then take your camera out of auto exposure mode and put it in manual (my recommendation) or aperture priority (if you prefer) mode. (Remember, I’m a landscape photographer so I never use shutter priority; if you’re shooting action, to better control the motion in your frame, you probably want to consider shutter priority if you don’t like manual exposure.)

Before metering, set your camera to whatever aperture you decide your composition calls for. Then meter, remembering that your camera isn’t telling you what the exposure should be, it’s telling you the exposure that will make what it sees a middle tone. Finally, correct the meter’s middle-tone bias by dialing in the shutter speed (in manual mode) or exposure compensation (in aperture priority) that gives the correct exposure.

After you click, check your histogram to be sure you got the exposure right.

What’s the correct exposure? That’s a creative choice that’s entirely up to you—feel free to play until you’re comfortable with your results. And the more you do it, the easier it gets.

For example

Below are some sample images and the thought process I followed to get the exposure.

Winter Reflection, El Capitan, Yosemite

Winter Reflection, El Capitan, Yosemite After choosing the aperture that gave me the depth of field I wanted, I spot-metered on the sunlit portion of El Capitan’s reflect (because it was the brightest thing in my frame and dialed my shutter speed until the meter indicated +2. That setting gave me enough light to resolve details in the shadows, but not so much light that the El Capitan highlights were blown out. If I’d have followed my meter’s “suggestion” to make El Capitan’s highlights a middle tone, the entire scene would have been too dark.

Here’s one matrix/evaluative metering would have made a mess of. The dynamic range (range of light between the darkest shadows and brightest highlights) was off the charts. Rather than compromise, I exposed to hold the color in the sky and let the foreground go to silhouette. I metered on the brightest (goldish) part of the sky next to Half Dome and dialed my exposure to +.3 (1/3 stop above middle tone). The sky was brighter than what you see here, but underexposing like this allowed me to emphasize the sky’s rich blue and the very Yosemite outline of Half Dome and Sentinel Dome. The highlights in the thin lunar crescent were clipped, but I didn’t care about the moon’s detail, only it’s shape.

Who says you should never blow your highlights? Here I metered on the brightest part of the poppy (near the top), setting my exposure to .7 (2/3 stop above middle tone). Everything you see that’s white is blown blue sky (except the “star,” which is a sliver of the sun).

Now get to work

Don’t wait to apply all this for the first time until you really, really want the shot. Instead, find a time when the results don’t matter and play with your camera to find out how much control you have over exposure. In fact, you can do this right now in your backyard or even sitting right there in your recliner. Meter something nearby, set an exposure, and click. Look at the result, adjust the exposure, and click again. Watch your histogram, and watch how its shape shifts right as you increase the exposure, or left as you decrease it. Continue doing this until you’re confident in your ability to make a scene brighter or darker, and can consistently achieve the exposure you expect.

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Taking Control in Difficult Light

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13 Comments on “Exposure basics

  1. Pingback: Are you insane?*: A control freak’s recipe for photographic success | Eloquent Nature by Gary Hart

  2. thank you for this article. As a person new to photography I find exposure one of the hardest things to master. This was helpful. I have read all of this before elsewhere, but some of your wording made it more clear to me.

  3. Hi Gary. Thank you for this informative article. I’m new into photography and appreciate you sharing these details.

  4. Pingback: Cameras are stupid | Eloquent Nature by Gary Hart

    • Price is based on supply and demand, not the cost of material or manufacturing–camera manufacturers will charge as much as people will pay. (Finally, an opportunity to use my economics degree.)

      • I’ve always held the opinion that it’s the photographer behind the camera that matters most, not the camera in his or her hand, that makes the difference between a mediocre photograph and a great one. Photography is art, and as such, it requires a creative mind behind the lens to choose the elements that will make the most powerful image. A higher-quality camera will not make an image taken by a professional photographer better, unless the difference between the two cameras is several levels of improvement (I would wouldn’t bother comparing my old 3.0 MP point-and-shoot Olympus with my Canon EOS 5D DSLR, for instance), but a better tool in the hands of a professional will make taking the same image a lot easier. The way I look at it, Michelangelo could have carved The Pieta with a flat rock and a box of butter knives if that’s all he had to work with — it just would have taken him longer — but with proper tools, he could create a masterpiece with less effort because he didn’t have to fight with his equipment.

  5. Gary, that is the most complete and easy to understand comparison between metering and exposure modes that I’ve ever read. After trying to figure that out on my own for years, and usually just choosing to shoot AV priority, I now (finally!!) understand the correct process for full manual. Love your tips, and love your photos even more. Thanks Gary!

  6. For casual travel photos I really like TAV mode, where I can choose my shutter speed AND f stop, then let the ISO float within a specified range. Most cameras can handle up to ISO 800 with very little image deterioration. That’s four stops of flexibility that we never had with film cameras.

  7. Gary this is by far the easiest to understand the basics of exposure. One has to decide what he/she wants to be the center of the picture before clicking the shutter.

  8. First of all, this is an awesome article because I have gotten to rethink my entire approach of shooting. Just one quick question: After adjusting the shutter speed, ISO, and the aperture, the camera shows the exposure is “right”. This “right” thing = the camera is happy with the middle tone of the overall scene. But the person behind the camera shouldn’t stop there. Because that’s letting the camera tell the photographer what to do. Right? The histogram still needs to be reviewed and the exposure could be further adjusted to ensure the outcome is to the photographer’s liking. Is my understanding on the right track?

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