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Tuesday, December 15, 2009

DSLRs For Low Light

The combination of improved sensors, advanced processing engines and powerful algorithms makes the current lineup of pro DSLRs capable of a whole new kind of low-light photography

Low-light and action photographers have long fought the good battle with the shutter-speed/aperture/ISO monster: You need a fast enough shutter speed to capture the action (or to prevent camera shake in handheld low-light shots), a small enough aperture to provide the needed depth of field and a low enough ISO to get good image quality. A quick look through the films selling at big photo dealers this morning reveals a fastest color-slide film of ISO 400, a fastest color-print film of ISO 1600 and a fastest black-and-white film of ISO 3200 (actually, ISO 1000; the EI rating indicates a “working” speed, not an official ISO speed).

Thanks to recent advances in sensor and image-processing technology, we now have DSLRs with low-noise, normal ISO settings of 12,800 and even 25,600, and two new models that provide expanded settings to an amazing 102,400. This means you no longer have to sweat the eternal trilogy: You can use a fast enough shutter speed and a small enough aperture and still get very good image quality. Of course, these technological advances also improve low-ISO image quality, so the newest-generation DSLRs can produce terrific image quality whatever your shooting needs. This means you can produce photos that not so long ago would have been impossible!

As a general rule, bigger pixels means better high-ISO performance (for example, Nikon’s 12.1-megapixel, full-frame D3S, with 8.45-micron pixels, produces better high-ISO image quality than the 12.3-megapixel, DX-format D300S with its 5.5-micron pixels), but there’s more to it than just pixel size. Sensor design considerations include such things as microlenses to give the photodiodes a more effective light-gathering area (newer microlenses are gapless and closer to the photodiodes to further enhance light-gathering ability and thus the signal-to-noise ratio), higher-transmission RGB filters over the photodiodes, better suppression of noise from off-sensor sources and improved preamps. More powerful processors can handle more elaborate algorithms, resulting in better image quality and overall camera performance—while some manufacturers are a bit secretive about their processors, Canon states that its latest DIGIC 4 has six times the processing power of its DIGIC III—and the new EOS 7D and EOS-1D Mark IV each use two DIGIC 4s. Image processing also has improved, both in-camera for JPEGs and RAW converters for RAW images (particularly in terms of high-ISO and long-exposure noise reduction). All of these things combine to give many of today’s DSLRs amazing high-ISO performance.


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