Final answer:
Allan Arbus, once partnered with Diane Arbus in photography, became an actor and appeared on the TV show MAS*H as Dr. Sidney Freedman in the 1970s.
Step-by-step explanation:
Allan Arbus, the ex-husband and former photography partner of Diane Arbus, transitioned from being a photographer to becoming an actor. In the 1970s, he appeared on the popular television show MAS*H, where he played the role of psychiatrist Dr. Sidney Freedman.
This was a significant shift from his partnership with Diane in the field of photography, which is well-chronicled and can be explored through various documentaries and texts that shed light on their contributions to the world of photography post-1960.