Decent Exposure: Mastering exposure is key to getting great images

Of all the primary elements a photographer controls–composition, focus, the moment the shutter is released, and of course the choice of the subject–none is more critical to making a great image than setting a proper exposure.  Some corrections to a poorly exposed image can be made in post-processing, and there are occasionally good artistic reasons to override the norms of exposure in order to evoke a certain mood in an image by making it darker or brighter than usual, but before we can effectively make these exceptional choices it is necessary to learn the basics of setting an appropriate exposure.

Let’s begin by defining exposure and the elements that comprise it.  Simply put, exposure refers to the amount of light that reaches the camera’s sensor and therefore how light or dark the resulting image will appear.  Four components together determine the exposure: 1) the brightness of the light reflecting off the subject and reaching the front of the lens, 2) the aperture setting on the lens (how wide or narrow is the opening of the lens), 3) the shutter speed setting (how long is the camera’s shutter open to allow light to strike the sensor), and 4) the sensitivity setting of the camera’s sensor.  We don’t always have control over the first component, but the other three are within our control using our camera’s settings.

Many photographers simply set their camera on Auto mode and let the camera’s built-in meter make its best guess as to how the image should be exposed.  That method can work well under certain conditions, but it is highly prone to errors.  For example, if your main subject is strongly backlit, the camera’s meter will expose for the average brightness in the scene and will underexpose the subject.  This is why so often we see underexposed photos of people standing outside in bright sunlight.

Although I compensated for the strong backlighting in this image of a Tibetan family enjoying a midday picnic, their faces are still quite shadowy, indicating a bit brighter exposure would have been better still.  Buy this photo

Fortunately, there are several easy methods to achieve a correct exposure even under challenging lighting conditions.  Here are a few that I use frequently:

  1. Set the camera’s metering mode to Spot Metering: By default most cameras’ metering systems use a sophisticated pattern-matching algorithm that measures how bright or dark each area of the image is and makes its best guess about a workable exposure based on similar scenes in the camera’s database.  Most cameras allow you to select a simpler metering mode called Spot Metering, that just measures the light at the central point in the image or another point that you select.  If you choose Spot Metering and select the measuring point to be right where your main subject is, you should get just the right exposure.
  2. Dial in some exposure compensation: Most cameras let you override the meter’s exposure setting by dialing in a compensation setting to lighten or darken the image.  If your subject is backlit, you will likely want to increase the exposure by one to two stops (each “stop” of additional exposure represents a doubling of the amount of light reaching the sensor).  The camera’s display should show something like “+1 EV” to alert you that you’ve dialed in 1 extra stop of exposure, and the number changes as you change the compensation setting.  Just be sure to set the exposure compensation back to zero when you’re done using it.
  3. Go fully manual: To gain complete control over your camera’s exposure settings, choose the meter’s Manual mode.  Then you can change all three exposure elements (shutter speed, aperture, and ISO) until the image appears properly exposed when you review it on your camera’s display.
  4. Use flash to increase the lighting on your main subject: One good way to achieve proper exposure with a backlit subject is to increase lighting on the subject itself, so that there is no longer such a difference in brightness between the subject and the background.  Your camera’s built-in flash may be strong enough to pull off this trick, but it often helps to have a more powerful flash unit with you.  There are some other reasons why you may not want to use flash as a main source of light on your subject, so this method should be used sparingly.  A reflector can be used instead of flash to reflect some of the sun’s light onto the front of your subject.

For this photo shoot with a musician friend, I shot into the light so she wouldn’t have to squint into the sun and also so that we’d have a beautiful rim light from the sun around her hair.  To pull this off, I used manual mode and selected the proper exposure for her face.  I employed a reflector to bounce some sunlight back onto her face and trumpet.  [Client image not for sale.]

Similar methods can be used for other challenging lighting conditions besides backlighting.  If the subject is a brighter or darker color than the “neutral gray” your camera’s meter uses for a standard, then you need to dial in more or less exposure as appropriate.  My black cat Dragonfly, for example, requires an especially dark exposure to override the meter from thinking he’s a gray cat and choosing too bright an exposure.  Similarly, a white polar bear will need additional exposure to stop the meter from underexposing what it assumes to be a gray bear.

When photographing a black subject, reduce the exposure to compensate for the light meter’s mistaken assumption that the subject is a neutral gray color.  Buy this photo

Whatever method you use to choose your exposure, be sure to take a look at the resulting image using your camera’s monitor.  Does the main subject appear to be properly exposed, or is it still too dark or perhaps too bright?  If your camera offers a histogram display, learn how it works and use it to check your exposure in tricky lighting conditions.  I’ll write a future post specifically about the histogram, as it is a very useful and often overlooked feature.

With some attention to the exposure of your images and use of some of the techniques described here, you can achieve a correctly exposed image nearly all of the time.  After mastering the essentials of exposure, you will have more keepers and fewer images in the virtual trash can, and you can even begin to break the rules for artistic effect.

Want to see more posts on photographic techniques?  You can find them all here: Posts on Techniques.

What lighting situations do you find the trickiest?  What techniques do you use to ensure properly exposed images?  Please share your thoughts in the comments box.


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