Photo Tip: All About Exposure

Reader Question: Which exposure mode should I use with my camera? What’s the difference between “Auto” and “A”?

My Answer: I’m going to start with a bit of background on the basics of camera settings. “A” refers to Aperture Priority mode. The user chooses the aperture and the camera automatically sets the appropriate shutter speed. Similarly, “S” stands for Shutter Priority, where the photographer chooses the shutter speed and the camera automatically chooses the appropriate aperture. “M” is for Manual, where the user selects both aperture and shutter speed — usually with the help of the in-camera meter.

“P,” or Program mode, is a bit of a hybrid. A simple explanation is that the photographer sets the aperture or shutter speed and the camera uses some built-in intelligence to make sure the picture does not result from a wrong setting. Usually a too-slow shutter speed would cause the picture to appear blurry. Program mode corrects for that.

The Auto setting is essentially the same as Program mode, but with one important difference: Auto wants the camera to produce a reasonably correct photo in all situations. Usually this is achieved by making the flash go off if the scene is the slightest bit dim. There’s a problem here, because it’s when a scene is starting to get dim that the interesting light that makes for great pictures happens. An indiscriminate flash can ruin the beauty of the scene. Another caution about Auto: it can cancel out specialized controls within the camera menu such as custom settings for saturation, sharpness, etc.

My recommendation: Most users would do well shooting with the Aperture Priority setting. But be careful and pay attention to the shutter speed produced by your chosen aperture, as it’s easy to forget that your lens is set to f/11 when you move from outdoors to indoors. If you leave that lens setting on, all of a sudden your indoor shutter speeds will be very slow (something you can actually hear, if you pay attention). If you find yourself being a little forgetful, switch to Program.

I’ve met many beginning photographers who have been told that if they aren’t shooting with their camera set on Manual, they’re not a real photographer. I would argue that the new version of “shooting in Manual” is to use one of the automated modes S, A, or P (but never Auto) but use exposure compensation to fine tune the setting.

Many cameras also have “Scene” modes. Usually these are indicated by little icons such as a portrait, flower, mountain, running person, etc. Those modes are great — much better than Auto — so give them a try.

My favorite “Scene” setting is the person with star or crescent moon icon (“Night Portrait”). This mode will keep the camera shutter open for a long time at night while using the flash to illuminate what’s in the foreground and freeze the action even though the shutter speed is slow. Experiment with this mode to capture amazing-looking pictures in the dark.

Most good cameras have a button marked with the +/- symbol. That’s the exposure compensation setting. A great way to work is to take a picture of a scene, check the histogram on the back of your camera, then set the exposure compensation to correct any over- or under-exposure. The histogram should, generally speaking, be centered. Then, after the compensation is set, you can look for interesting things to take pictures of. Re-set your compensation only when you notice that something drastic has changed in the scene. Experienced photographers use the histogram to check exposure instead of trusting what the picture looks like on the back of the camera.

In the photo above, I didn’t want to be bothering with Manual mode because we were within 10 yards of the North Pole and, as you can see, we were all focused on looking for it. I had originally dialed in +2/3 exposure because all the white in the scene tricked the camera’s meter into making the picture look too dark. I didn’t want the snow to appear completely white, so I only partially compensated, but the histogram helped me determine the best setting. Usually I use Aperture mode, but in this case my camera kept rubbing against my jacket and messing with the aperture settings. So, I switched to Program mode to stop that from happening.

Dan Westergren is director of photography for National Geographic Traveler magazine. Follow him on Twitter @dwestergren and on Instagram @danwestergren.

Do you have something you want to ask Dan about travel photography? He’ll be answering reader questions periodically on the blog, so be sure to leave a comment.