thanks all,
the lens are the same : Yashinon 80mm, for the view 2,8 and the film 3,5
The negatives are nice, very sharp, there's no other problem.
Yes the image in my viewfinder is smaller than the one on the film.
The focussing screen seems to be the first, not change...
So You don't have the same error on your Yashica Mat, just the parallax in the height ?