Question #7a413

It may be easy to remember by thinking of a "cave" going into a mountain. Concave curves extend inward. It IS possible for a single lens to have both concave (inner) and convex (outer) surfaces. "Flat" is just flat - a planar surface.

Many lenses are made from plate glass by grinding only one side, leaving a flat or planar surface on one side, and a convex or concave one on the other. Lenses may also be made with either convex or concave surfaces on BOTH sides.

Just remember, if you have to reach in to touch the center, it is concave, if the center sticks out from the lens it is convex.

"Optical design" and all the rest are the details of how to shape those surfaces and materials to get particular desired optical properties.

Optical Design would be the entire assembly, from a single lens up to a full telescope or microscope. It would be the type, dimensions and placement of each optical element to achieve the desired resolution and magnification.

Optical Structure could include some of that, but would more likely be specific to the individual pieces, e.g. one lens. It would define the geometric shape of the lens to obtain the desired optical properties. The structure would be were a lens is defined as concave or convex, as well as the desired curvature of that form.

In “ancient” descriptions there really is not difference between the terms “Design” and “Structure”. They were usually concerned with describing the entire optical mechanism.