In the 1970s and 80s – back when dinosaurs grazed under the el on Wabash – I worked as a camera assistant on episodic tv shows and commercials. We mainly shot 35mm film and composed within an image area known as TV Safe Action. This had an aspect ratio of 4:3 and measured approximately 18mm X 14mm.
We used a simple rule of thumb to determine the distance needed to achieve the field of view for a head and shoulders closeup at any focal length: divide the lens focal length by ten and express the result in feet and inches. For example, 45mm÷10 = 4.5 = 4 feet 6 inches or 150mm÷10 = 15 = 15 feet. Within a given format, this simple formula will give you the same field of view at the point of focus.
We used this mainly to match image size between closeups, but it was also useful for placing the slate so that it could be easily read by the editor. It is also a useful baseline for extrapolation: halve the focal length or double the distance and you get a field of view twice as high and wide. Conversely, double the focal length or halve the distance and you get a field of view that is half as high and wide.
Notes on the illustrations –
Each set of illustrations show the field of view for 25mm @ 2’6”, 50mm @ 5’ and 75mm @ 7’6” for the designated format.
If the illustrations were actual photographic images with foreground and background elements, wide angle and telephoto effects would come into play. Nonetheless, within each format, the field of view at the point of focus is consistent.
The illustrated field of view is the area within the light blue background.