The use of plano convex lens in a slide projector

[NumFront]

Hello

My question has two parts:
1) Why is plano convex lens used in slide projector? Why can't we use simple convex lens in it?
2) Why are two plano convex lenses used in slide projector? Why can't we use only one?Thanks!

 

[Andy Resnick]

Hello

My question has two parts:
1) Why is plano convex lens used in slide projector? Why can't we use simple convex lens in it?
2) Why are two plano convex lenses used in slide projector? Why can't we use only one?

Without knowing any specifics, it's hard to say why specific design choices were made. In general, tho: positive lens elements (plano-convex or biconvex) are often chosen rather than negative elements because they are easier to manufacture and mount. Multiple lens elements are used (rather, a single element is split into two) as a method to reduce aberrations (see, for example, the rapid rectilinear design) I expect that spherical and coma are corrected at a minimum (aplanat), and possibly astigmatism and field curvature (anastigmats).

Does that help?

 

[sophiecentaur]

Hello

My question has two parts:
1) Why is plano convex lens used in slide projector? Why can't we use simple convex lens in it?
2) Why are two plano convex lenses used in slide projector? Why can't we use only one?Thanks!

Yes - that was something I noticed too. Perhaps having two such lenses allows easier positioning than you could get with one lens with two high domed sides. Those lenses are in the Condenser Unit so would Chromatic Aberration be a significant problem? The condenser systems I've seen don't seem to be high quality units.