Back in the 80's I wanted the best 35mm projector available. The Leitz projector was the best and had the sharpest glass and you could view a slide as long as you wanted and the projector wouldn't burn the slide up.
Unfortunately, I couldn't afford the Leitz so I bought a Kodak and put a Schneider lens on it. I had really close to the quality of the Leitz lens at a fraction of the cost. Of course I still had a cheap projector that would burn up the slides if I kept them in too long.