October 18, 2007 2:02 PM PDT

Canon has fix for high-end SLR autofocus

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An adjustment to one mirror should fix an autofocus problem that has tarnished the debut of Canon's high-end EOS-1D Mark III camera, the company said Thursday.

Canon's EOS-1D Mark III

(Credit: Canon)

"We're pretty confident this countermeasure will resolve the issue completely," said Chuck Westfall, a Canon spokesman and tech guru. "It feels nice to have a little bit of light at the end of the tunnel and know it's not another oncoming train."

The $4,500 camera, geared chiefly for photojournalists who can appreciate features such as its 10.5-frame-per-second shooting ability, had won accolades for most of its design. But photographer and consultant Rob Galbraith dug up problems that cropped up in bright or warm conditions. The problems were also confirmed by others including Seattle Times photographer Rod Mar.

Canon was able to reproduce the problems. "What we found out after our thorough research is this issue seemed to manifest itself more in cases where the temperature was high," Westfall said.

Not all cameras are affected, but Canon doesn't know which are or aren't, so anyone having the problem should send the camera in to be repaired, Westfall said. Once it's ready to begin repairs, Canon will publish instructions on how what photographers should do, probably in the next two or three weeks.

New cameras coming off the line don't have the problem, he said.

The problem involves a mirror that directs light to the camera's autofocus subsystem. "That mirror needs to be adjusted," Westfall said.

Single-lens reflex (SLR) cameras have a main mirror that directs light from the lens to the viewfinder, so photographers can see what they're shooting. But some light passes through that mirror, traveling instead to sub-mirrors that direct light to the autofocus system's sensor. When a photographer takes a picture, both the main mirror and the sub-mirror for the autofocus system flip out of the way to let light shine on the camera's main image sensor.

The problem with the sub-mirror could mean the camera would focus in front of the subject or behind it, Westfall said. "If that sensor is not receiving reliable information, it's not able to carry out correct focus prediction," he said.

(Via Rob Galbraith.)

Originally posted at Underexposed

Stephen Shankland writes about a wide range of technology and products, but has a particular focus on browsers and digital photography. He joined CNET News in 1998 and since then also has covered Google, Yahoo, servers, supercomputing, Linux and open-source software, and science. E-mail Stephen, or follow him on Twitter at http://www.twitter.com/stshank.