PhotoPlus Expo opened in New York City today and we made a bee-line to the Canon booth to check out the just announced EOS 1D Mark IV. We sat down with Chuck Westfall, Canon's technical guru, and talked to him about what Canon has done to control image noise when shooting at the camera's high ISO settings.

Though the Mark IV is able to shoot at ISOs higher than its predecessor, the 10MP Mark III, the size of the individual pixels in the new camera are smaller because of the higher resolution. Pixels in the 16-megapixel Mark IV are 5.7 microns compared to 7.2 microns in the Mark III. Both cameras use APS-H sized (27.9 x 18.6mm) chips with a magnification factor of 1.3x.

Westfall said Canon has redesigned the architecture of the Mark IV's CMOS image sensor to compensate for the smaller pixel size.

"The wells for each diode got a little deeper," he told us. "Even though the diodes got smaller, they're storing a lot of light on each one. Also, the microlenses on the sensor are now 'gapless' and they're moved closer to the diode so you lose less light."

Westfall noted that as on the 5D Mark II, the color filter array on top of the Mark IV's sensor has been reformulated and the new material is more transparent to let in more light.

"Also, the actual circuitry on the sensor has changed," he said. "The amplifier they're using to get that signal out of the chip is more powerful. So you're getting a stronger signal."

In addition to changes at the sensor level, the Mark IV is powered by two new Digic IV processors which also help reduce noise, he said.

"So the camera is one stop better based on the chip improvements and one stop better based on the Digic IV processors."