Credit from the back: Teatterimuseon Kokoelmat; Toivo Niskanen (1887–1961) & Ja Margit Lilius (s. 1899); Chopin: Valssi 1917
Credit from the back: Teatterimuseon Kokoelmat; Lucia Nifontova (1913–1987) & Arvo Martikainen (1905–1946); Tshaikovski: Prinsessa Ruusunen 1938
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Found these postcards in the shop of The Finnish Museum of Photography in Helsinki
Ballet Photography 
I am from Finland so I can help with those credits wich are in finnish! :) Both photos are from Collections of The Theatre Museum (of Finland) and first picture is from Chopins Waltz -ballet and second from Tshaikovskis Sleeping Beauty. Hope there was anything interesting for you. :)