I was recently given an old projector which can take both 35mm and 6 * 6 slides. The holder for 6*6 slides takes two slides at once, so doing a whole slide show would be a faltering process.

I have about 20 slide mounts, but most of my medium format E6 images are 6*7, so I'm planning to put some Velvia and Provia through a Yashicamat to get some images and try out the projector, just for an experiment.