Originally posted by: Mike O

I though that GTW wasn't filmed in widescreen, as it didn't exist?

You're right, GWTW wasn't shot in widescreen, it was shot in academy ratio like every other film in 1939.
Widescreen films did exist in the 1930s, but very few films were shot that way back then.
Widescreen Museum LINK

I did a little research, and VistaVision was invented by Paramount in 1954.
VistaVision LINK
So, there's no possible way that a VistaVision camera was used on the set of GWTW. Aside from the fact that VistaVision was invented 15 years after GWTW was released, VistaVision cameras used single-strip negatives. Gone With The Wind was shot with 3-strip Technicolor cameras, which were the size of large kitchen appliances and were extremely difficult to maneuver.
See photo HERE.

I know that the VistaVision cameras were used to shoot many classic films, but Gone With The Wind was not one of them.