Low-Light Compromises

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Today’s Question: This approach [of capturing a bracketed sequence of exposures to assemble in to a high dynamic range image] works with a stationary or nearly stationary object. Would the same advice be offered if you were shooting candid photos or some action scene? For example, an indoor sport where the lighting was overhead and fairly constant and only the players kept moving.

Tim’s Quick Answer: When there is any significant motion in a scene (especially a key subject that is moving), a bracketed exposure to create a high dynamic range (HDR) image will be difficult if not impossible. In that type of situation your only real option is to compromise on detail for either the highlights or shadows, and possibly to compromise on overall exposure settings.

More Detail: By definition, capturing bracketed exposures for an HDR image requires more time than a single capture. To begin with, you will generally be capturing several exposures with different shutter speeds. In addition, you will likely be capturing three or more individual exposures, which increases the total amount of time for the capture (even if you can use relatively fast shutter speeds for all of the exposures).

As a result, with any significant amount of motion in the scene you may need to limit yourself to a single exposure. That will involve a compromise in terms of total detail in the image, as well as a compromise in terms of overall noise levels for the photo.

By opting for a single exposure rather than an HDR created from a bracketed sequence of exposures, you’ll be covering a narrower tonal range for the scene. That means you will likely need to choose between sacrificing highlight detail versus shadow detail. As a general rule it is preferred that highlight detail be preserved at the expense of shadow detail. However, that may vary depending on the specifics of the scene you’re photographing. The point is that you’ll need to make a decision about the overall exposure that involves a degree of compromise relative to detail in the image.

In addition, with movement in the scene you may need to compromise on other camera settings. It might be necessary to sacrifice depth of field, for example, opening up the aperture more than you might otherwise want to in order to allow more light for a faster shutter speed.

You might also need to increase the ISO setting beyond your normal comfort level, in order to ensure a shutter speed that is fast enough to avoid (or minimize) apparent motion blur in your captures. This will obviously increase the amount of noise in the photo, due to the effects of amplification applied based on the higher ISO setting.

Of course, having less depth of field or more noise in the capture is probably better than having motion blur in the photo. The specific decisions you make will depend on your own priorities for photographing the scene. The key is to be aware of the consequences of each decision you’re making, so you can make a better decision about the specific compromises involved.