I've been taking a night photography class through the Smithsonian, and we've had NO issues when out taking night shots with view cameras on tripods. I was shooting at the Lincoln, along the reflecting pool, and at the WW II, with nary a peep from a security guard. Same over at the Native American museum. Only time I've been hassled was one night I was trying to shoot the carousel on the mall, and the park police came zooming over to determine if I was doing it commercially. Which I wasn't.