Quote Originally Posted by Rick A View Post
I'm a little confused. Are you using the same film with different backs, or different film in different backs? If the former, its the film. If the later, its a camera problem.
Sorry, I guess my strange English sentences don't help

I tried two kind of films packs, a Polaroid 554 and Fuji FP100-c45, in the same polaroid 550 holder. The problem come from this holder for sure, but I don't understand what is happening.