Thanks for the thoughtful responses. Scissors aren't the optimal solution since I need to do this in high quantities - and it really needs to be perfect.
Also, let me clarify what I need to do...I'm taking unmounted 35mm slide transparencies, and need to punch out the entire "image" area. Not for destruction, but perfectly preserved since that's the piece I'm using.
I have a device that accomplishes what I need for a smaller area within the slide. You can see it here: (the link isn't being permitted here)
But I'm trying to avoid having a similar device custom made ($1500+) for punching out the full image area, and so I'm posting here to see if anybody has come across such a device. My apologies if I wasn't clear enough in my original post.