The Case of the Screaming Woman - S1-E30
Visible crew/equipment: When Paul Drake opens the door to enter Perry Mason's office, the black-gloved hand of a crew member can be seen in the hallway.
Perry Mason (1957)
1 visible crew/equipment mistake in season 1 - chronological order
Starring: Raymond Burr, Barbara Hale, Ray Collins, William Hopper
The Case of the Wayward Wife - S3-E13
Revealing mistake: Perry and Della step into an elevator but there is no line in the floor between the floor they are on and the elevator floor. It's continuous.
Hamilton Burger: Incompetent, irrelevant, and immaterial.