I'd seen a photograph a couple of years ago, taken by Atto Kim over 8 hours in Times Square. It stuck with me, how people and traffic dissolved leaving only stationary buildings and traces of humanity. It wasn't dehumanizing, it was more of a merging of humanity and architecture. If I remember correctly, Kim used a few panes of welding glass mounted over the lens of his camera to block almost all of the light. Unfortunately, I can't remember where I read the article on his series, or saw the photo originally. Google searching turns up snippets, but not the description of process that I vaguely remember.

I dabble with some long exposures, using a CPF to drop it down a couple of stops, but nothing like what Kim had done.

The photo that really stuck in my head was this one:

8 hours of times square

Photo by Atta Kim

Kim's work features lots of long exposures - portraits that include traces of motion, cityscapes merging humanity into static architecture, and other conceptual art pieces that play with motion and time. Very interesting stuff, both aesthetically and technically. Unfortunately, his photographs are largely locked behind a crappy opaque Flash website.