When David Turnley, ’77, a Pulitzer Prize-winning photographer, sent U-M Head Football Coach Jim Harbaugh, ’86, a signed photo he had taken of Nelson Mandela in prison, it launched both a deep friendship and an ambitious book project. Their collaboration led to “Enthusiasm Unknown to Mankind.” The black-and-white pictorial book showcases Turnley’s images of Harbaugh’s first season as U-M coach and includes a 9,000-word essay by Harbaugh that outlines 15 principles on which Michigan’s football program is built.

In early August, Michigan Alumnus caught up with the two men in Harbaugh’s office, where he reflected on the subtle methods Turnley used to convince him to allow the team to be photographed daily for 16 months and counting. (Turnley is still snapping away.)

“David is a very good twister of arms, in a very good way,” mused Harbaugh of Turnley, a photojournalist who has covered conflicts all over the world, from the Gulf War to 9/11. “You don’t know David is twisting your arm until he is. I think it comes from his years of experience having to talk his way through war zones.”

The two graduates had much in common even before they first met in February 2015. Both had just arrived back on campus after a long hiatus away and at the height of their careers. But far more unusual, they have the added distinction of having brothers who work in the same professions. Turnley’s identical twin brother, Peter, ’77, is also a photojournalist of international distinction; “60 Minutes” profiled the two of them in 1996 in an interview titled “Double Exposure.” And Harbaugh’s older brother, John, is the head coach for the Baltimore Ravens. In 2012, when Jim was coaching the San Francisco 49ers, the brothers faced off against each other in the Super Bowl.

To view some of Turnley’s most compelling images and read highlights from the co-author’s 40-minute discussion, check out the fall 2016 issue of Michigan Alumnus, which arrives in homes in mid-September.

But for now, here is a glimpse of images from the book, available for purchase in late August at M Den locations and on the publishing website FosterPark.net.

The “Michigan Fanatics” edition (12×9.5) runs at $75, while a larger 17×14 version costs $150. And for serious fans, an autographed collector’s edition (17×14) is on sale for $250.