First of all: Film is amazing. I am constantly shocked by what's "in there," even when it pulls the curtain back a little too far, and spoils the illusion.
Case in point:
The original Falcon/Hangar shot was done by compositing a photo of the top of the model with the live set, blended by a bit of paint work. Here you can clearly see the delineation between the three layers - a delineation which was actually quite obvious in the final composite. This would obviously never pass muster today, yet it didn't seem to stop Star Wars from making a couple-two-three dollars...
_Mike