[TYPO3] Image zoom for all pictures?

[Jens Beckmann]

Hi,

I want to set the image zoom (click on the thumbnail) to any pictures on 
my site. I tried to set in the template:

   tt_content.image.20.1.imageLinkWrap.enable.field.image_zoom >
   tt_content.image.20.1.imageLinkWrap.enable.field.image_zoom =1

or

   tt_content.image_zoom = 1


... but it didn't work. I cant't find the right entry. I have hidden the 
  zoom checkbox in the backend.

Any suggestions?
Thanks
Jens