Framing 35mm slides for projection
Hi, I have just visited my friend who has Leica Pradovit 300 IR projector (with the 90/2.5 lens). It was really a treat, but it was not possible to get the whole image sharp. As the wall was flat ;) I have check a few of the slides and indeed one could see a slight "bulging" of the film in the frames - maybe around 1mm - but it was obviously enough to cause problems.
Just a note - he is using glass-less mounts of "newer" type whatever that means - definitely compatible with his projector.
So - I would like to ask - how do you make sure that your framed slides are nicely flat? Glass mounts? Special mounting? Are some particular mount more suitable than others?
I am asking as I may finally get a 35mm camera just to be able to project slides - it really looks cool (No, I do not plan to get into projecting 6x6 slides as of now)