16mm is a standard film format, so named because of its 16-millimetre width.
It was the usual format of choice for location filming until the programme switched exclusively to 1" Type C videotape during season 23. Consequently, it was the film stock used when a strike forced the whole of Spearhead from Space to go on location. Spearhead is the only Doctor Who story entirely filmed on 16mm, though many others have large sections recorded in the format.
Additionally, it was the preferred format for telerecording. Almost every 1960s and early 1970s episode which survives as a telerecording does so in 16mm.[1]
Footnotes
- ↑ Exceptions are "The Waking Ally", The Wheel in Space episode 6, The Krotons episode 1, The Seeds of Death episode 5, and The Space Pirates episode 2, which are in 35mm.