Quote Originally Posted by pentaxuser View Post
A new one on me. I wonder how this one works? Anyone care to explain in simple optical terms?
In theory, it shouldn't work as any point on the negative should be projected onto the same place on the paper from all areas of the lens.

Something I did years ago when my father was having a slide show was to cover up half of the lens with my hand thinking it would block out half of the image. Instead you get the whole image at a reduced brightness.