In some places, you'll see that there is a large 
image which a studio doesn't pan across, but more 
focuses in. In the same way as when you're zooming
in when you're using normal film. I've always 
been under the impression that these are the 
oversized cels. If they start from a smaller cel, 
by the time they have zoomed in fully, the 
quality isn't as high as it would be if the cel 
had been bigger to begin with.

I think there are a lot of cels billed as
"oversize" which are actually pan cels. A good 
for example is my Nightwalker cel of Shidou and 
Riho on the couch in his office. Here is how it 
is used: They do a short pan of just over half 
the cel, then switch to another (completely 
different) shot, then do a second short pan - 
closer up - of the other half of the cel. So is 
it a pan, or an oversized? ^_^;;  I call it 
oversize because the pans are so short. But it 
really is both, I guess.

Many Sharp Smiles,
--Drac (if any of this makes any sense. . . ^_^)