Glass mounts are still available; problem is, you have to mount the slides between the paper-thin glass pieces yourself. They are designed to keep slides flat. Without them, slides will "pop" as they get warm, which you can see as going out of focus. Most projectors and lenses are not designed for glass mounts, but the autofocus feature should refocus a slide that pops out of focus. Both my Kindermann and Rollei do this. If your Braun has autofocus, it should refocus slides that go out of focus. Or you can just do it manually by slightly rotating the lens. A flat-field lens is supposedly best for glass-mounted slides; using a regular projection lens might give you out-of-focus edges on screen. If your projector literature does not say anything about using glass slides, I'd be willing to bet it and its lens were designed for regular, non-glass, slide mounts.
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