Captain McBain wrote:
Were holograms in use during the TOS era?
Looking at The Original Series in isolation? Not by Starfleet.
Looking at the greater Trek universe, yes holograms were used in the TOS era. The technology was available in-universe but simply not seen due to 1960's TV budget/FX constraints. They had the Rec Room holodeck in the animated episode "The Practical Joker", a whole century earlier we saw lots of holograms in the Enterprise TV series (including seeing the NX-01 crew practicing by shooting holographic targets and the Romulans using holographgic technology to disguise one of their ships), and in the last movie we saw holographic heads-up displays on the USS Kelvin and the new Enterprise. Oh, and holographic games were seen in the TMP rec room and the bar McCoy visited in TSFS.