Originally Posted by sdai
I'm not an optics engineer, barely a technical person in mind ... can anyone explain to me if and why a simpler optical design could bring some better results than what I can get from a more sophisticated (which may directly translates into technically advanced in my dictionary) construction?
In lens designs, "simpler" (fewer elements, less-complex surfaces, etc.) is always better than "more sophisticated" (more elements, exotic surfaces) all other things being equal.
"All other things" in this context refers to the performance criteria demanded of the lens -- sharpness, contrast, freedom from aberrations and distortion, etc.
In other words, if you're a designer and you can choose from a simpler design or a more complex design, both of which have similar theoretical performance, you always choose the simpler design. Why? Because the performance of a lens inevitably involves a certain amount of randomness. This includes both large-scale variation, such as in tolerances during assembly, and very tiny variation -- the unavoidable quantum randomness in the behavior of individual light photons when they encounter the surface of the lens.
The fewer lens surfaces, the fewer opportunities for these random behaviors to produce undesirable results. Or to put it even more briefly: Simpler designs have less risk of something going wrong.
In the old days of high-performance lens design (say, the 1920s through the 1950s) a lens with ambitious design goals such as large maximum aperture, low distortion, high sharpness, and wide angular coverage inevitably required a complex, "sophisticated" assembly with a lot of elements. (Scale down the goals and the job got much simpler: If you're satisfied with a 2-degree angular coverage and a maximum aperture of, say, f/8 or smaller, a lens with only two elements can do an excellent job.) There were several reasons all this complexity was needed: the range of glass types available was limited, and the fact that all design calculations had to be done manually limited the range of options the designer could try.
Now, however, there is a more sophisticated understanding of how light behaves when passing through a lens, made possible in part by advanced computer modeling; and there also are a wider range of sophisticated glass types, surface shapes, and assembly processes available. This greater sophistication has translated into the fact that a "simpler" lens design (fewer elements, fewer groups, less exotic curvatures) can yield higher
performance than a very complicated lens of days gone by.
It has always been true that the simplest lens that will do the job is the best; it only has been recently that technology has advanced enough to make it possible for the lens that will do the job to be simple!