When I asked filmmaker Greg Kohs why it took him so long – eight years – to make his documentary Song Sung Blue, he got quiet.

"Why did it take me only eight years?" he rephrased the question. Then he headed back into a long contemplative silence. "Because that’s how long it took me to capture enough compelling material for a clear beginning, middle and end," he finally said.

This kind of thoughtfulness is what makes Song Sung Blue "not your typical tribute band film," as Kohs puts it. The documentary follows a rocky decade in the lives of Lightening & Thunder, a husband-and-wife duo from Milwaukee who sing sets of Neil Diamond, ABBA and Patsy Cline songs.

Kohs, 41, got to know the pair in 1993 while shooting a commercial film for Harley-Davidson in Milwaukee. Lightening & Thunder (a.k.a. Mike and Claire Sardina) "were huge in Milwaukee, Madison and Chicago in the 90s. They had a large fanatical following among college students," he said. The Frogs, Urge Overkill and Garbage were all fans of the act.

Their fame peaked in 1995 when Eddie Vedder invited Lightening & Thunder up on stage to play an encore at a Pearl Jam show for 30,000 people at Summerfest.

Then, tragedy hit.

"It was like something out of Spinal Tap. You know how they always talk about losing someone to ‘a bizarre gardening accident’? That’s what happened to Lightening & Thunder. And that’s where I entered their lives," Kohs said.

It was a difficult situation to be in as a filmmaker. On one hand, he wanted to help them. "I was rooting for them," he said.

But after looking at footage from his first visit to film them, he realized that he hadn’t really captured them: "I didn’t see (in the footage) what I had seen (while filming) because I had been part of their story."

So, in his subsequent visits to Milwaukee, he pulled back, became a fly on the wall and let the drama unfold.

Kohs, who lives near Philidelphia, directs television commercials fulltime. Working on an independent project like Song Sung Blue gave Kohs a freedom he normally doesn’t encounter in the commercial world.

"I didn’t have any rules. The idea of ‘what do people want to see?’ didn’t really influence the filming. It was what I wanted to see. It was a lot more painful doing it myself, but it’s also why I enjoyed it so much. It’s like the burn a runner experiences," he said.

Song Sung Blue won the best documentary award at the 2008 Slamdance Film Festival. Variety reviewer Dennis Harvey wrote that "the personalities on display are so distinctive that Song Sung Blue manages to be compelling without being too much of a downer, or condescending in its view."

Kohs said his first priority right now is to "shepherd this film through the festival circuit," but he does have his eye on a few future independent projects, one of which is a story revolving around a "meteorological incident" that took place in the Upper Peninsula in 1913.