Wow, some of these are super cool

Gauguin, Manet, Rembrandt and Whistler sketches, Weston nudes, Harry Callahan photos, amazing things indeed.

People generally seem quite uninterested in preparatory sketches/studies/maquettes by famous artists, which is absolute madness, to my mind. Unfinished and transitory work is much more interesting to me. Photographers' contact sheets especially.