I suppose you mean "Atget" by Szarkowski? Szarkowski used Atget as a paradigmatic case for certain views he had about photography as a whole. The four volume series (which I don't have) seems to be a more complete version, incorporating Hambourg's groundbreaking discovery about Atget's indexing system. There's been a lot of academic sparring ever since on whether Szarkowski presented Atget in an anachronistic manner; whether he dressed him up to fit his agenda, so to speak. In this context, the Szarkowski/Hambourg edition is important as it illustrates more fully Szarkowski's views on Atget and his development as a photographer. Mostly interesting if you want to have a better understanding of the debate, or if you are a diehard Atget fun who wants to dive into a bigger portion of his archive.
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