I think the somber tone of his photos is due to our perspective on his work. Atget was truly one of the world's most gifted photographers but most, if not all, of his photographs were made to sell as a way to earn a living. As we look at them today, we can't help but feel a sensation of loss since the Paris he loved and photographed is no more. It's a bittersweet experience to view Atget's photos.
".... interesting that a lot of the atget collection at the george eastman house was the former collection of man ray."
If I remember correctly, Atget was idolized by the surrealists of the day. | 
Linear Mode
