Tuesday, June 9, 2009
Breaking The ISO Barrier
Forget the megapixel race. The real digital revolution is in low-noise/high-ISO digital capture.
It’s obviously nice to shoot with higher ISOs that allow for low-light handholding in situations that wouldn’t have worked with film. But what about the million other ways that low-noise/high-ISO digital capture has changed the game? What’s so special about increased sensor sensitivity that it makes photographers rave about a brave new world of image-making?
To paraphrase Gerd Ludwig, low-noise/high-ISO digital capture has finally given photographers the ability to provide a sense of place in pictures in ways that were previously impossible. A sense of place in a photograph? That could be useful.
Why are digital sensors capable of producing better-looking images at higher ISOs than film? To increase the sensitivity of films, manufacturers use larger crystals, or grains, of silver halide—the light-sensitive part of a film emulsion. In layman’s terms, larger grains are more capable of capturing more light photons to be developed in the darkroom. The trade-off? Larger crystals create visibly larger grains in the finished image.
Though the process works quite differently with digital capture, there are parallels between the electronic version and the chemical one. The counterpart to a film’s grains of silver are the pixels on a CCD or CMOS sensor. These pixels, as is so often explained, act like buckets catching the rain of photons that falls on the sensor. A bigger bucket—a bigger pixel—captures more photons. While this doesn’t make a bigger pixel inherently more light-sensitive than a smaller pixel, it does increase the signal-to-noise ratio, which means that a bigger pixel is capable of producing a cleaner, more noise-free image than its smaller-pixel cousins.
Growth in sensor and pixel size—always balanced against the growth in resolution that comes from packing more and smaller pixels on a sensor—has translated into higher sensitivity with lower noise than most film photographers ever would have dreamed possible. Today’s full-frame and larger digital sensors not only have the physical properties that allow for inherently cleaner signals, but the benefits of a solid decade of improvements to the image-processing algorithms that convert those signals to visual images. Every new generation of cameras has brought not only more megapixels, but cleaner pixels, too.
Now that super-sensitive, low-noise digital capture is a reality, how are photographers putting it to use? Increased capabilities in low-light situations are an obvious improvement, but the benefits go far beyond shooting in the dark.
Photographer Tyler Stableford uses his cameras’ high-ISO capabilities to stop fast action—be it in bright sunlight or the last rays of the day. Stopping fast-moving subjects requires a fast shutter speed; a fast shutter speed requires a wider aperture—or a higher ISO.
“I like to shoot with sunbursts in my sports images,” Stableford says, “and this is only possible with an aperture of ƒ/16 or narrower. They’re so bright and sunny that you wouldn’t normally think that you’d need high-ISO capabilities, but you do. If I want to stop the action of ski jumping, I need to push the ISO to 800 or beyond to achieve a shutter speed of 1⁄500 second. This is particularly true when trying to shoot sunbursts at sunset, when the light is most beautiful; here, I have to go above ISO 1000. This simply wasn’t possible until recently.”
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