Wow.. so many factors, so much math.. grin I've taken about 3 optics classes and still couldn't tell you anything very specific about lens-making.. I've mostly learned the theory and math behind how they work. So, basics: lenses can be made with pretty much any refractive material (it's why a round bowl filled with water can be a fire hazard if it's in direct sunlight or why your eyes work when they're 90% water). From what I know from school though, most lenses are made from glass materials with formulas specific to the manufacturer. The reason because glass is mostly predictable as far as structure goes during manufacture (although a chemist would be able to tell you more about this - I only took as far as basic organic chemistry, myself). Polishing, from the little "field trip" we took to the National Research Centre back in college, seemed to be mostly made with sandblasting and water (for large mirrors and lenses) all the way down to very fine, high-power lasers (for very small pieces, i.e. fiber optics systems). Lasers in general are used to measure the lenses' properties, at least on the prototype, too. As to why some are better than others.. I'd say that most of the time it's because they're better suited for the job than others. While one lens may have less physical aberration (shape 'interference'), it might have more chromatic aberrations (color 'interference'), etc etc. So one lens for regular camera use might be excellent over another that sucks, while the situation is the exact opposite for, say, communications (shape reproduction is highly important in the former, while the latter might be more interested in the duration of the pulse of light itself). The whole manufacturing process is also a big factor, and the batch itself (you can get lemons in anything). Also, experience from the manufacturer helps a lot (math only takes you so far - the physical world tends to be quite different). So, anyway, I'm probably useless to you, but your post seemed lonely. :) - darkpen