Everybody knows that when you mount a 200mm lens on a D70 (or any other camera with a "1.5 factor"), the lens "becomes a 300". Here's a demonstration which shows that this is not true:
If you look at Case 1, the moon is the same size in both the film and the DSLR image. If the focal length had been multiplied by 1.5, the moon would be 1.5 times bigger on the DSLR image. In the DSLR image the moon does take up more of the total image area, but that's because the image area is smaller, not because the moon is bigger.
This seems to be conclusive proof that there is no change to the focal length of a lens when it is mounted on a DSLR.