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The RAW Image Stabilizer—03/05/12

How to use underexposure as an alternative to an image stabilized lens

This Article Features Photo Zoom

Let's take a bit of a scientific approach to this week's tip by writing it out as an "if/then" statement. If we can agree that a RAW image file retains significant image-forming detail in both shadows and highlights; and if we can agree that shadows and highlights are prevalent in under- and over-exposed image files; and if we can agree that RAW image files have an increased latitude that allows those over- or under-exposed image files to be "recovered" into the realm of a "correct" exposure with basic RAW postproduction techniques; THEN we can agree that it is possible to rescue an under- or over-exposed image in RAW processing and make it look like a normal exposure that was made in the camera and this whole convoluted process never happened in the first place.

What's the point of all this doublespeak? I'm going to draw a parallel between underexposing RAW image files and an awesome image stabilizer for your lens—and I'm going to base it on that premise that we can turn underexposed images into normal ones with basic RAW processing. Here's how.

If a RAW image file retains image-forming detail in a photo that has been underexposed by as much as two stops, then you can underexpose your picture deliberately by as much as two stops and create a perfect exposure in post. Why would you want to do this? Simple: to get a faster shutter speed that will eliminate camera shake.

Underexposed

Let's say you're working with a 105mm prime lens, and the light is low and you've cranked the ISO to 2000 but you just don't care to go any higher. And let's say that the correct shutter speed to ensure a sharp handheld photo with this lens is at least 1/125th of a second. And let's assume that the correct corresponding aperture to make a "correct" normal exposure is ƒ/2. Then you're all set: for the light and ISO and lens your ideal exposure should be 1/125th at ƒ/2. But what if your lens only opens up to ƒ/4? You're fully two stops underexposed.

In normal circumstances you might adjust the ISO higher—to ISO 8000—in order to create the correct exposure. But then you get a whole lot more digital noise. Or maybe you'd simply slow the shutter speed two stops to 1/30th. But then you'd surely get motion blur with the 105mm lens. If you had a lens with Vibration Reduction technology built in, you'd enable it and shoot the correct exposure. But your lens doesn't have Image Stabilization. So what can you do? Simple: you let the power of the RAW image file stand in for the stabilizer.

You keep the shutter speed at 1/125th to ensure the image is sharp and free of camera shake, you keep the ISO at ƒ/4 and you underexpose your image by the full two stops. Then, because you're shooting RAW and it's got such a high dynamic range, you pull out the necessary detail in post-production and enjoy your normal looking image—all made possible thanks to the dynamic range of RAW. It's for that reason that RAW image files can stand in for image stabilization technology. And you don't even have to buy a new lens to take advantage of it.

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