Exposure basics

Lunar Kiss, Half Dome and Sentinel Dome (and crescent moon), Yosemite
Canon EOS-1Ds Mark III
5 seconds
F/7.1
ISO 200
135 mm

Want to totally confuse your camera? Try auto-exposing a scene like this. (Details below.)

Cameras aren’t so bright

Your camera is stupid. Sorry (so is mine). And while I’ll gladly 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, your camera will do everything in its power to make it a middle tone. Sunlit snow? Asphalt at midnight? It doesn’t matter—if you let your camera decide, it will turn out gray.

Modern technology from camera manufacturers offers faux-intelligence to help overcome this limitation. Their solution, called “matrix” or “evaluative” metering, compares a scene to a large but finite internal database of choices, returning a metering decision based on the closest match. This works pretty well in conventional, “tourist” light, but often struggles mightily in the warm or dramatic light artistic photographers prefer. 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

We (or our camera) control the amount of light in our images with our shutter speed, f-stop, and ISO settings, adding or subtracting “stops” of light by increasing or decreasing the shutter speed, f-stop, or ISO. A stop is the measurement of light photographers use, much as a cup (of sugar or almonds) is a measurement of volume that cooks use.

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

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

For example, let’s say you’re photographing fall leaves in a light breeze. You got the exposure right, but the leaves are blurred and decide you need to double your shutter speed to freeze the leaves’ motion. Making the shutter open and close twice as fast reduces the amount of light by one stop, but it also means not as much light will reach your camera’s sensor. To replace that lost light, you could open your aperture more (change the f-stop), double the ISO, or do a combination of fractional f-stop and ISO adjustments that total one stop).

Metering modes

Your camera’s metering mode determines the amount of the frame the meter “sees.” 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. The larger the area your meter sees, the greater the potential for a wide range of tones.

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 isn’t available in all cameras—in some, the most precise (smallest metering zone) 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 SLR (single lens reflex) and mirrorless cameras offer manual, aperture priority, shutter priority, and a variety of program or automatic exposure modes. Serious landscape photographers should forego the full automatic/program modes in favor of manual (my recommendation) or aperture/shutter priority modes that offer more control.

If you select aperture priority mode (I’m a landscape photographer, so I’m assuming people reading this are as well), you specify the aperture (f-stop) and the camera sets the shutter speed 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 unlikely), you then need to use dial the exposure compensation (usually a button with a +/- symbol) to adjust the amount you want your subject to be above or below a middle tone.

For example, if you point your meter at a bright, sunlit cloud, the camera will only give it (and the rest of your picture) enough light make the cloud a middle tone, and you end up with a picture that’s too dark (if the cloud’s the brightest thing in the frame, making it a middle tone means everything else in the frame is too dark). You need 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 it gives me more control, and I think it’s 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 (sorry), 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), and 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—there’s 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. Others 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, the first thing I do is check the brightness of their 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. It’s 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.

Expose yourself

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 may 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.

What’s the correct exposure? That’s a creative decision that’s entirely up to you—feel free to play until you’re comfortable with your results. 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 try to apply all this for the first time when 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.

:: More photography tips ::

Taking Control in Difficult Light

Click an image for a closer look, and a slide show. Refresh the screen to reorder the display.

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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