Thanks! I've been going crazy trying to figure this out. Appreciate it. -Norm
With the current version of iPhoto you cannot fix the zoom to any percentage. There is no way to know when you are at precisely 100%. Old versions were able to do it. You may want to consider Aperture.
I realize this is an old thread, but I don't like leaving incorrect posts uncorrected, for the sake of futures wanderers who find the thread through a search...no offsense intended.
That said, in iPhoto you can zoom to 100% by pressing 1 or 200% by pressing 2 (which corresponds to dragging the zoom slider all the way to the right). I admit, arbitrary percentages are not easy to achieve (to my knowledge), and zooming to 200% is easy since it corresponds to the end of the slider...but zooming to 100% is difficult without knowing the '1'-key trick.
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