Originally Posted by codename_47:
“The idea to have the Tardis doors open out immediately onto the exterior in the modern series was a good one, it allows the drama to be more immediate than it was with the setup on the original series Tardis, where it was implied there was a sort of corridor between the control room and the exterior. As far as I know they never showed this on screen though.
I assume the only way it was set up with the "dead space" in the original series was they lacked the green screen technology to allow them to show the Tardis interior behind the characters every time they entered or exited.”
There are indeed some episodes that seem to imply this "sort of corridor".
The Claws of Axos is perhaps one instance of this, as there seems to be a short corridor between the TARDIS interior and exterior doors.
However, in the Hartnell era, there are several occasions where it is made plain that the doors open directly on to the exterior, and what look like thick white doors with roundels from inside the TARDIS look like Police Box doors from outside (
The Edge of Destruction,
The Sensorites, and
The Web Planet, for example, all show this). This was usually done by shooting out of the TARDIS set onto a portion of the exterior set as the travellers went out, then cutting to a reverse shot on the exterior set with the Police Box prop in position behind them. The doors in this second shot would be closing, so that you could not see the TARDIS interior through them (as you say, this could not have been done convincingly with the technology available).
Later, in
Pyramids of Mars, CSO is used to provide an outward-looking shot from within the TARDIS that seems to imply direct access to the outside ("1980, Sarah, if you want to get off"), and there may be others that I have forgotten.
The use of Police Box doors inside the TARDIS in the revived version has always seemed to me lazy and unimaginative. The very first episode was not afraid to have Barbara go through the external Police Box doors into an entirely alien environment in which the doors themselves have assumed an entirely different form. RTD funked it.
[The above is all done from memory, I'm afraid, so please excuse any errors of detail. I believe the general premise is sound.]