Telecentric Lens

Hello! I'm working on duplicating the optics experiment outlined here: http://www.lhup.edu/~dsimanek/scenario/labman3/telecen.htm

The gist is using a lens with a small aperture at the focal point to filter out light rays that are not perpendicular to the lens, creating an image without perspective distortion.

I'm trying this with a fresnel lens, it's about 8"x10", and the focal distance is [very] roughly 9".

I can get it to the point of what is basically a camera obscura (pictured below), but I'm finding the setup as I understand it does not yield the results described in the experiment. When I place an aperture in the focal plane and move the screen material back to where the aperture should focus, I still see the same image as below, still inverted.

I'm hoping someone with more optics expertise could help me troubleshoot. Thanks!

ps, this is not really homework for me, I'm interested in this more as a photography project.