Lighthouse enthusiasts are buoyed by a federal lawsuit in Michigan that could return a long-lost and valuable piece of maritime history to South Portland.

The coveted object is a 120-year-old Fresnel lens that once was a beacon for mariners coming into Portland Harbor. The 2-foot-tall, 15-inch-wide lens was a marvel of modern technology when it was installed at the Spring Point Ledge Lighthouse in 1897.

Through a series of five prisms, it was capable of throwing a pencil-like beam of light more than 20 miles, or about twice the distance of a conventional lens. Modern-day lenses still mimic that design.

The glass lens, designed by French physicist and engineer Augustin-Jean Fresnel, resembles a giant beehive. It was originally purchased for $3,200 in the late 1800s and is now estimated to be worth $250,000.

“It’s a beautiful lens,” said Keith Thompson, chairman of the board of trustees for the Spring Point Ledge Lighthouse. “We didn’t know whether it was destroyed or crated up at a Coast Guard depot somewhere and forgot about. We just didn’t know.”

The lens disappeared from the Spring Point Ledge Lighthouse in 1960, after the U.S. Coast Guard automated the lighthouse. Instead of having a lighthouse keeper stoke the signal with a mineral oil lamp, the light house was electrified.

“When those lenses were removed, we weren’t really focused on historic preservation,” said Bob Trapani Jr., executive director of the American Lighthouse Foundation in Owls Head. “No one was looking at these artifacts as ‘artifacts.’ Some of the lenses were destroyed. Some were taken back to Coast Guard facilities, and others just disappeared.”

The missing 120-year-old Fresnel lens was installed in 1897 at the Spring Point Ledge Lighthouse and served as a beacon for mariners coming into Portland Harbor. Photo courtesy of the Spring Point Ledge Lighthouse Trust

All of Maine’s 66 lighthouses were outfitted with Fresnel lenses, Trapani said. Only eight are still in use today, he said. They are at Seguin Lighthouse off Popham Beach, West Quoddy Head Lighthouse in Lubec, Pemaquid Point, Cape Neddick, Owls Head, Browns Head near Vinalhaven, Bass Harbor Head and Fort Point near Stockton Springs.

Overall, the location of about 30 of Maine’s Fresnel lenses are known, according to the United States Lighthouse Society.

Although the Spring Point Ledge lens, estimated to weigh between 265 and 440 pounds, was supposed to remain in the Coast Guard’s possession, it somehow wound up in the hands of a collector in Michigan. Now the U.S. Department of Justice is suing on behalf of the Coast Guard to have the lens returned.

According to federal court documents filed Sept. 6 in U.S. District Court in the Eastern District of Michigan, the last known owner of the lens is Steven Gronow, who runs the Maritime Exchange Museum in Howell, Michigan. The museum specializes in the collection, restoration and sale of lighthouse antiques, including Fresnel lenses, according to its website.

The lawsuit also is seeking the return of a lens manufactured in 1880 that was originally used in the Belle Isle Lighthouse in Michigan. Slightly larger than the Spring Point Ledge lens, it has an estimated value of $350,000.

Gronow did not return a phone call or email seeking comment Monday evening. But the Associated Press reported that Gronow would not say whether he still had the lenses.

“I’m not saying I have them anymore,” said Gronow, 59, of Genoa Township, Michigan. “It would probably be smart for me not to say anything. They could be gone.”

The lawsuit says both lenses were offered for sale on Dec. 23, 2009, on Gronow’s website and other websites. Gronow has ignored attempts by the Coast Guard to get more information about how they were acquired, as well as requests to have them returned, the lawsuit says.

The work order to remove the Spring Point Ledge lens makes it clear that it would remain the property of the Coast Guard, which now has strict protocols for handling the lenses, the lawsuit says.

The lawsuit claims that the lenses were moved to Gronow’s attorney’s office in Northville, Michigan, on Nov. 26, 2014, and returned to Gronow sometime in late 2015 or early 2016.

Thompson said he traced the lens to Michigan through the United States Lighthouse Society’s database of Fresnel lenses back in 2009. Around the same time, he got a call from the Coast Guard curator the lens had been found.

He said his heart sank in 2010 when he saw Gronow’s entire collection listed on eBay for $2 million. Apparently, the collection did not sell.

“We really want to get that lens back,” Thompson said. “It’s a part of South Portland’s maritime history and we want people to be able to see it.”

The trust has recently received two grants, totaling $12,000, to help finance $20,000 in needed repairs to the lighthouse. Thompson hopes that if the federal government prevails, he will be able to display the lens in the assistant keepers quarters in Spring Point Ledge Lighthouse, provided it can comply with the Coast Guard’s standards, including being able to afford insurance.

“It’s a beautiful lens and it appears to be in remarkably good shape,” Thompson said. “They’re basically works of art at this point. It’s part of our lighthouse. It’s a huge piece of the puzzle.”