Kanagawa lens producer making ‘eye’ for world’s largest telescope



A lens maker in Sagamihara, Kanagawa Prefecture, is busy finishing work on the “eye” of what will be the world’s largest telescope, now under construction near the summit of Mauna Kea in Hawaii.

The primary mirror of the Thirty Meter Telescope is scheduled to be completed in March 2022. It will be composed of 492 hexagonal mirrors, each 72 cm across. Ohara Inc. is supplying 574 mirrors, including some that will be used as replacements, by March 2020.

The TMT, with a 30-meter aperture, is larger than Japan’s Subaru Telescope, one of the world’s biggest to date. It is also near the top of the 4,205-meter-high volcano and entered service in 1999.

The TMT’s light-condensing capabilities are 13 times greater than the Subaru Telescope, allowing an object as small as a ¥1 coin to be identified at a distance equivalent to that between Tokyo and Osaka.

Ohara has dedicated itself to the TMT, a joint project involving Japan, the United States, China, Canada and India, since losing the order for the Subaru’s mirror to a pair of American companies.

“We really wanted an order for the TMT,” said Hiroyuki Minamikawa, the official who was put in charge of the project at Ohara.

Minamikawa, 44, read about the TMT concept in a U.S. research paper in 2003 and began studying it to win the order. After three years of research, he concluded that non-expansion glass, which barely expands when temperatures rise, would be indispensable.

Ohara began experiments in 2006 to examine the effects of sharp changes in temperature on glass and created a system for mass producing non-expansion glass in 2012.

Founded in 1935, Ohara’s previous achievements include an order to make an observation system for Apollo 11, the U.S. space mission that put the first man on the moon in 1969.

The glass expands by less than 0.00002 mm per meter per degree of temperature change.

The TMT has a resolution four times sharper than the Subaru’s single main mirror, which is 8.2 meters wide.

“I cannot imagine a mirror as large as 30 meters,” Minamikawa said. “I wonder what we can see on it.”

The most distant and oldest star so far observed was born some 800 million years after the Big Bang. The universe is believed to be 13.8 billion years old.

The TMT will help astronomers observe stars born 200 million to 400 million years after the Big Bang.