1.Robert Adams at Matthew Marks522 W. 22nd St., nr. Tenth Ave; 212-243-0200For his new series “Turning Back,” the photographer followed Lewis and Clark’s path across the Northwest Territory—in reverse.2. Alec Soth at Gagosian 555 W. 24th St., nr. Eleventh Ave; 212-741-1111“Niagara,” new work exploring love and loss from the young artist behind last year’s lyrical series “Sleeping by the Mississippi.”3. Juergen Teller at Lehmann Maupin540 W. 26th St., nr. Eleventh Ave; 212-255-2923Personal and public history intersect in “Nürnberg,” portraits of the photographer’s kin taken in the former National Socialist capital.