Oedipus Rex (film vs text)

In the film Oedipus the King produced by the Royal Shakespeare Company we are presented with a modernistic adaptation of Sophocles' classic Greek tragedy. A Greek tragedy essentially consists of the story of something terrible happening to a person of noble stature, such as Oedipus who is a prince and a king. Oedipus Rex is considered to be one of the greatest masterpieces to emerge from the period when Greek drama was dominant. Oedipus' popularity was not only restricted to the Ancient Greeks but also continued to receive time on the stage as the centuries continued to pass by, even up to the present day. This in a sense took part in breaking a tradition, because plays in Greece were more or less restricted to one performance, but later the Greeks came to appreciate the classic works, and the most popular would be revived, one of which was Oedipus Rex.
The opening shot of the film presents us with a fairly decent visual representation of what Sophocles seemed to have in mind for the beginning of the play. The outer steps of the castle are crowded with what seem to be peasants who are obviously in different states of peril. When Oedipus exits the castle into the courtyard to confront the peasants the actor playing the role does an excellent job of portraying the cocky swagger and demeanor that Sophocles seemed to bestow upon him on the page. Although we quickly notice that none of the actors are wearing masks, which would have been the case had this been a production that was taking place in the time of the Ancient Greeks, which brings up another point. There are a large number of actors in this play ranging from the peasants to the chorus to the main characters themselves where as this would not have been the case had it been produced in fourth century (BC) Greece. During the time of Greek Drama, plays were acted out by 2 to 4 actors who took all the roles of the play upon themselves, which is where the importance of masks came into effect in order to help the audience distinguish between different characters.
The Royal Shakespeare Company has taken Oedipus Rex and made some changes with it in their film, some of which make sense and some others that do not seem to make sense in my eyes. The fact that they used more than 2 to 4 actors seems to be a logical decision by today's standards and essentially only takes away a small portion of the play and may even help it's dramatic effect. The company also took the clothes and costumes of the characters and modernized their look, which strikes me as odd because this seems to take away a large portion of the visual affect. The biggest change that seemed noticeable to me was the fact that the R.S.C. decided to take the script and update the dialogue with today's language and structure. Even though the play follows the same timeline of events and gets the same point across, I still feel that this was an unnecessary change, which more or less transforms this it into a completely different play. It has become The Royal Shakespeare Company's Oedipus Rex and is no longer Sophocles' Oedipus Rex.