Question about Thon rings

[Eduardo Sanz-Garcia]

I have a question about Thon rings. I have realized recently that when I 
take pictures using the CCD camera I get better Thon rings than when I 
take the image using film (less rings and more diffuse). The specimen is 
the same in both cases and the intensity of the beam is adjusted 
automatically in both cases. I am using a Technai  F30.
Any clue why the film is giving me worse result than CCD?
Thank you in advance for your suggestions. I will appreciate them a lot.