Here's a good thing to remember the next time your autofocus hunts in low light, or your memory card fills up at the wrong moment. The photographers who pointed a camera at armed conflict 160 years ago had to coat a glass plate with volatile chemicals, load it into a hefty wooden camera not far off the size of a small trunk, expose it for several seconds, then develop it in a darkroom wagon before the emulsion dried. Usually within ten minutes.
This is the context worth holding in mind as the National Gallery of Art in Washington DC announces the acquisition of 35 photographs documenting America's Civil War: a collection it describes as marking "a seminal moment in the history of photography".
