If you want to see Adams and Weston, you're better off looking for commercial galleries that carry their work. While MoMA and the Metropolitan certainly have them in their collections, they're not usually on display (check the museums' websites for current exhibit listings... most of MoMA is curated temporary exhibits, IIRC, and the Metropolitan usually has one or two temporary photography exhibits along with a very small sampling from their permanent collection. ICP is almost always showing 2-3 temporary exhibits.