Hello guys, I´ve been reading this site for a long while, and decided to register. I´ve got a simple question: When you have a hologram of a character speaking... Do you have to put "O.S." in his/her dialogue? Thanks in advance.

Hmmm...interesting question. I think...I think I would just have the hologram speak the words:

       RIMMER HOLOGRAM
Greetings peasants.

instead of:

Lister speaks to Rimmer's Hologram.
 
        RIMMER (V.O.)
Greetings peasants.


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Is this what you were asking?
Hope this helps,
MacDuff

Add to that --

       RIMMER HOLOGRAM
Greetings peasants.

          LISTER
Smeg off!

(-- Sorry, love Red Dwarf and couldn't resist!!)

I think that the hologram is still a visual character, albeit slightly transparant, therefore it should have a regular speaking part.

If you can't see them at all, then V.O would work, I think...

It's cold outside there's no kind of atmosphere, I'm all alone, more or less, let me fly far away from here, far far....in the sun, sun sun.....

That the character is a hologram should be in the character's description.

R2-D2 projects a hologram of PRINCESS LEIA onto the table.

                LEIA
  Help me, Obi-wan Kenobi.
  You're my only hope.

I believe putting LEIA HOLOGRAM as the character name would be improper since that would imply that the hologram is a different character than Leia herself is. This ruling is overturned pretty much ONLY if Leia and her hologram were in the same room and you had to differentiate the two dialogues, but if that were the case, they would be different characters.

Thank you very much for your help, people.