Alfred Stieglitz was 54 when Georgia arrived in New York...23 years her senior. Educated in Berlin, he had studied engineering and photography before returning to the States at the turn of the century and opening the 291 gallery. He pioneered the art of photography, and single-handedly introduced America to the works of Picasso, Matisse, and Cezanne at the gallery...along with publishing his well respected "Camera Works" magazine.
Shortly after her arrival, Alfred took Georgia up to the Stieglitz family home at Lake George in the Adirondack Mountains. They would return to the lake home each summer for years to come. Georgia produced many paintings of the Lake George countryside during these years.
Stieglitz had become obsessed with photographing Georgia since the beginning of their relationship. He would take over 300 portraits of her between 1918 and 1937. Most of the more erotic poses would be in the first few years of their marriage. Read more here

Georgia O'Keeffe—Hand and Breasts
1919
1919
The photographs of O'Keeffe taken in those first twenty four months document the most intense, passionate, and complex transaction ever recorded between a man and woman by a camera. Stieglitz's portrait embraces the most public and private extremes of O'Keeffe's being: icons of a remote, enigmatic woman that merged with her paintings to create her identity as artist together with sexual explorations of her body so intimate they have yet to be published
Alfred Stieglitz and Georgia O'Keeffe
Arnold Newman
1942
Sources:
(1997.61.19) | Heilbrunn Timeline of Art History | The Metropolitan Museum of Art)