Bingowings said:
The building though real is about half the size of the building it's meant to be in the film so they had to put the speeder in post as it would be to the wrong scale otherwise.
Interesting, could be the reason they went with an optical alternative. It actually never occured to me.
Top: John Jympson Cut Below: Film Version
Looking at them again side-by-side, I think they did the right choice even if the angle and composition of the shot is a bit uninspiring, the doorway seen straight on in the Jympson cut could be another factor for their choice. The interior scenes was originally actually timed quite dark compared to the earlier video releases where it was often incorrectly timed quite bright, but I guess that's a bit too much, we later also see windows in the set for the interior. Talking about the doorway, the nights must have been freezing cold, I would have invested in a door if I was Ben. ;)
As for clear blue skies vs cloudy skies discussed earlier, they also had to struggle keep matching adjacent shots as good as possible back then whereas nowadays you do all that in the computer, there's sometimes a lot of time between takes and different scenes when shooting a film which made these things difficult when you're on location.